Linux下端口扫描程序nmap介绍

摘要
　　nmap是一个网络探测和安全扫描程序，系统管理者和个人可以使用这个软件扫描大型的网络，获取那台主机正在运行以及提供什么服务等信息。nmap支持很多扫描技术，例如：UDP、TCP connect()、TCP SYN(半开扫描)、ftp代理(bounce攻击)、反向标志、ICMP、FIN、ACK扫描、圣诞树(Xmas Tree)、SYN扫描和null扫描。从扫描类型一节可以得到细节。nmap还提供了一些高级的特征，例如：通过TCP/IP协议栈特征探测操作系统类型，秘密扫描，动态延时和重传计算，并行扫描，通过并行ping扫描探测关闭的主机，诱饵扫描，避开端口过滤检测，直接RPC扫描(无须端口影射)，碎片扫描，以及灵活的目标和端口设定.

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1.名称

nmap-网络探测和安全扫描工具

2.语法

nmap [Scan Type(s)] [Options]

3.描述

　　nmap是一个网络探测和安全扫描程序，系统管理者和个人可以使用这个软件扫描大型的网络，获取那台主机正在运行以及提供什么服务等信息。nmap支持很多扫描技术，例如：UDP、TCP connect()、TCP SYN(半开扫描)、ftp代理(bounce攻击)、反向标志、ICMP、FIN、ACK扫描、圣诞树(Xmas Tree)、SYN扫描和null扫描。从扫描类型一节可以得到细节。nmap还提供了一些高级的特征，例如：通过TCP/IP协议栈特征探测操作系统类型，秘密扫描，动态延时和重传计算，并行扫描，通过并行ping扫描探测关闭的主机，诱饵扫描，避开端口过滤检测，直接RPC扫描(无须端口影射)，碎片扫描，以及灵活的目标和端口设定。

　　为了提高nmap在non-root状态下的性能，软件的设计者付出了很大的努力。很不幸，一些内核界面(例如raw socket)需要在root状态下使用。所以应该尽可能在root使用nmap。

　　nmap运行通常会得到被扫描主机端口的列表。nmap总会给出well known端口的服务名(如果可能)、端口号、状态和协议等信息。每个端口的状态有：open、filtered、unfiltered。open状态意味着目标主机能够在这个端口使用accept()系统调用接受连接。filtered状态表示：防火墙、包过滤和其它的网络安全软件掩盖了这个端口，禁止 nmap探测其是否打开。unfiltered表示：这个端口关闭，并且没有防火墙/包过滤软件来隔离nmap的探测企图。通常情况下，端口的状态基本都是unfiltered状态，只有在大多数被扫描的端口处于filtered状态下，才会显示处于unfiltered状态的端口。

　　根据使用的功能选项，nmap也可以报告远程主机的下列特征：使用的操作系统、TCP序列、运行绑定到每个端口上的应用程序的用户名、DNS名、主机地址是否是欺骗地址、以及其它一些东西。

4.功能选项

　　功能选项可以组合使用。一些功能选项只能够在某种扫描模式下使用。nmap会自动识别无效或者不支持的功能选项组合，并向用户发出警告信息。

　　如果你是有经验的用户，可以略过结尾的示例一节。可以使用nmap -h快速列出功能选项的列表。

4.1 扫描类型

　　-sT
　　TCP connect()扫描：这是最基本的TCP扫描方式。connect()是一种系统调用，由操作系统提供，用来打开一个连接。如果目标端口有程序监听， connect()就会成功返回，否则这个端口是不可达的。这项技术最大的优点是，你勿需root权限。任何UNIX用户都可以自由使用这个系统调用。这种扫描很容易被检测到，在目标主机的日志中会记录大批的连接请求以及错误信息。
　　-sS
　　TCP同步扫描(TCP SYN)：因为不必全部打开一个TCP连接，所以这项技术通常称为半开扫描(half-open)。你可以发出一个TCP同步包(SYN)，然后等待回应。如果对方返回SYN|ACK(响应)包就表示目标端口正在监听；如果返回RST数据包，就表示目标端口没有监听程序；如果收到一个SYN|ACK包，源主机就会马上发出一个RST(复位)数据包断开和目标主机的连接，这实际上有我们的操作系统内核自动完成的。这项技术最大的好处是，很少有系统能够把这记入系统日志。不过，你需要root权限来定制SYN数据包。
　　-sF -sF -sN
　　秘密FIN数据包扫描、圣诞树(Xmas Tree)、空(Null)扫描模式：即使SYN扫描都无法确定的情况下使用。一些防火墙和包过滤软件能够对发送到被限制端口的SYN数据包进行监视，而且有些程序比如synlogger和courtney能够检测那些扫描。这些高级的扫描方式可以逃过这些干扰。这些扫描方式的理论依据是：关闭的端口需要对你的探测包回应RST包，而打开的端口必需忽略有问题的包(参考RFC 793第64页)。FIN扫描使用暴露的FIN数据包来探测，而圣诞树扫描打开数据包的FIN、URG和PUSH标志。不幸的是，微软决定完全忽略这个标准，另起炉灶。所以这种扫描方式对Windows95/NT无效。不过，从另外的角度讲，可以使用这种方式来分别两种不同的平台。如果使用这种扫描方式可以发现打开的端口，你就可以确定目标注意运行的不是Windows系统。如果使用-sF、-sX或者-sN扫描显示所有的端口都是关闭的，而使用SYN扫描显示有打开的端口，你可以确定目标主机可能运行的是Windwos系统。现在这种方式没有什么太大的用处，因为nmap有内嵌的操作系统检测功能。还有其它几个系统使用和windows同样的处理方式，包括Cisco、BSDI、HP/UX、MYS、IRIX。在应该抛弃数据包时，以上这些系统都会从打开的端口发出复位数据包。
　　-sP
　　ping扫描：有时你只是想知道此时网络上哪些主机正在运行。通过向你指定的网络内的每个IP地址发送ICMP echo请求数据包，nmap就可以完成这项任务。如果主机正在运行就会作出响应。不幸的是，一些站点例如：microsoft.com阻塞ICMP echo请求数据包。然而，在默认的情况下nmap也能够向80端口发送TCP ack包，如果你收到一个RST包，就表示主机正在运行。nmap使用的第三种技术是：发送一个SYN包，然后等待一个RST或者SYN/ACK包。对于非root用户，nmap使用connect()方法。
　　在默认的情况下(root用户)，nmap并行使用ICMP和ACK技术。
　　注意，nmap在任何情况下都会进行ping扫描，只有目标主机处于运行状态，才会进行后续的扫描。如果你只是想知道目标主机是否运行，而不想进行其它扫描，才会用到这个选项。
　　-sU
　　UDP扫描：如果你想知道在某台主机上提供哪些UDP(用户数据报协议,RFC768)服务，可以使用这种扫描方法。nmap首先向目标主机的每个端口发出一个0字节的UDP包，如果我们收到端口不可达的ICMP消息，端口就是关闭的，否则我们就假设它是打开的。
　　有些人可能会想UDP扫描是没有什么意思的。但是，我经常会想到最近出现的solaris rpcbind缺陷。rpcbind隐藏在一个未公开的UDP端口上，这个端口号大于32770。所以即使端口111(portmap的众所周知端口号) 被防火墙阻塞有关系。但是你能发现大于30000的哪个端口上有程序正在监听吗?使用UDP扫描就能！cDc Back Orifice的后门程序就隐藏在Windows主机的一个可配置的UDP端口中。不考虑一些通常的安全缺陷，一些服务例如:snmp、tftp、NFS 使用UDP协议。不幸的是，UDP扫描有时非常缓慢，因为大多数主机限制ICMP错误信息的比例(在RFC1812中的建议)。例如，在Linux内核中 (在net/ipv4/icmp.h文件中)限制每4秒钟只能出现80条目标不可达的ICMP消息，如果超过这个比例，就会给1/4秒钟的处罚。 solaris的限制更加严格，每秒钟只允许出现大约2条ICMP不可达消息，这样，使扫描更加缓慢。nmap会检测这个限制的比例，减缓发送速度，而不是发送大量的将被目标主机丢弃的无用数据包。
　　不过Micro$oft忽略了RFC1812的这个建议，不对这个比例做任何的限制。所以我们可以能够快速扫描运行Win95/NT的主机上的所有65K个端口。
　　-sA
　　ACK扫描：这项高级的扫描方法通常用来穿过防火墙的规则集。通常情况下，这有助于确定一个防火墙是功能比较完善的或者是一个简单的包过滤程序，只是阻塞进入的SYN包。
　　这种扫描是向特定的端口发送ACK包(使用随机的应答/序列号)。如果返回一个RST包，这个端口就标记为unfiltered状态。如果什么都没有返回，或者返回一个不可达ICMP消息，这个端口就归入filtered类。注意，nmap通常不输出unfiltered的端口，所以在输出中通常不显示所有被探测的端口。显然，这种扫描方式不能找出处于打开状态的端口。
　　-sW
　　对滑动窗口的扫描：这项高级扫描技术非常类似于ACK扫描，除了它有时可以检测到处于打开状态的端口，因为滑动窗口的大小是不规则的，有些操作系统可以报告其大小。这些系统至少包括：某些版本的AIX、Amiga、BeOS、BSDI、Cray、Tru64 UNIX、DG/UX、OpenVMS、Digital UNIX、OpenBSD、OpenStep、QNX、Rhapsody、SunOS 4.x、Ultrix、VAX、VXWORKS。从nmap-hackers邮件3列表的文档中可以得到完整的列表。
　　-sR
　　RPC扫描。这种方法和nmap的其它不同的端口扫描方法结合使用。选择所有处于打开状态的端口向它们发出SunRPC程序的NULL命令，以确定它们是否是RPC端口，如果是，就确定是哪种软件及其版本号。因此你能够获得防火墙的一些信息。诱饵扫描现在还不能和RPC扫描结合使用。
　　-b
　　FTP反弹攻击(bounce attack):FTP协议(RFC 959)有一个很有意思的特征，它支持代理FTP连接。也就是说，我能够从evil.com连接到FTP服务器target.com，并且可以要求这台 FTP服务器为自己发送Internet上任何地方的文件！1985年，RFC959完成时，这个特征就能很好地工作了。然而，在今天的Internet 中，我们不能让人们劫持FTP服务器，让它向Internet上的任意节点发送数据。如同Hobbit在1995年写的文章中所说的，这个协议"能够用来做投递虚拟的不可达邮件和新闻，进入各种站点的服务器,填满硬盘，跳过防火墙，以及其它的骚扰活动，而且很难进行追踪"。我们可以使用这个特征，在一台代理FTP服务器扫描TCP端口。因此，你需要连接到防火墙后面的一台FTP服务器，接着进行端口扫描。如果在这台FTP服务器中有可读写的目录，你还可以向目标端口任意发送数据(不过nmap不能为你做这些)。
　　传递给-b功能选项的参数是你要作为代理的FTP服务器。语法格式为：
　　-b username:password@server:port。
　　除了server以外，其余都是可选的。如果你想知道什么服务器有这种缺陷，可以参考我在Phrack 51发表的文章。还可以在nmap的站点得到这篇文章的最新版本。

4.2 通用选项

　　这些内容不是必需的，但是很有用。

　　-P0
　　在扫描之前，不必ping主机。有些网络的防火墙不允许ICMP echo请求穿过，使用这个选项可以对这些网络进行扫描。microsoft.com就是一个例子，因此在扫描这个站点时，你应该一直使用-P0或者-PT 80选项。
　　-PT
　　扫描之前，使用TCP ping确定哪些主机正在运行。nmap不是通过发送ICMP echo请求包然后等待响应来实现这种功能，而是向目标网络(或者单一主机)发出TCP ACK包然后等待回应。如果主机正在运行就会返回RST包。只有在目标网络/主机阻塞了ping包，而仍旧允许你对其进行扫描时，这个选项才有效。对于非 root用户，我们使用connect()系统调用来实现这项功能。使用-PT <端口号>来设定目标端口。默认的端口号是80，因为这个端口通常不会被过滤。
　　-PS
　　对于root用户，这个选项让nmap使用SYN包而不是ACK包来对目标主机进行扫描。如果主机正在运行就返回一个RST包(或者一个SYN/ACK包)。
　　-PI
　　设置这个选项，让nmap使用真正的ping(ICMP echo请求)来扫描目标主机是否正在运行。使用这个选项让nmap发现正在运行的主机的同时，nmap也会对你的直接子网广播地址进行观察。直接子网广播地址一些外部可达的IP地址，把外部的包转换为一个内向的IP广播包，向一个计算机子网发送。这些IP广播包应该删除，因为会造成拒绝服务攻击(例如 smurf)。
　　-PB
　　这是默认的ping扫描选项。它使用ACK(-PT)和ICMP(-PI)两种扫描类型并行扫描。如果防火墙能够过滤其中一种包，使用这种方法，你就能够穿过防火墙。
　　-O
　　这个选项激活对TCP/IP指纹特征(fingerprinting)的扫描，获得远程主机的标志。换句话说，nmap使用一些技术检测目标主机操作系统网络协议栈的特征。nmap使用这些信息建立远程主机的指纹特征，把它和已知的操作系统指纹特征数据库做比较，就可以知道目标主机操作系统的类型。
　　-I
　　这个选项打开nmap的反向标志扫描功能。Dave Goldsmith 1996年向bugtap发出的邮件注意到这个协议，ident协议(rfc 1413)允许使用TCP连接给出任何进程拥有者的用户名，即使这个进程并没有初始化连接。例如，你可以连接到HTTP端口，接着使用identd确定这个服务器是否由root用户运行。这种扫描只能在同目标端口建立完全的TCP连接时(例如：-sT扫描选项)才能成功。使用-I选项是，远程主机的 identd精灵进程就会查询在每个打开的端口上监听的进程的拥有者。显然，如果远程主机没有运行identd程序，这种扫描方法无效。
　　-f
　　这个选项使nmap使用碎片IP数据包发送SYN、FIN、XMAS、NULL。使用碎片数据包增加包过滤、入侵检测系统的难度，使其无法知道你的企图。不过，要慎重使用这个选项！有些程序在处理这些碎片包时会有麻烦，我最喜欢的嗅探器在接受到碎片包的头36个字节时，就会发生 segmentation faulted。因此，在nmap中使用了24个字节的碎片数据包。虽然包过滤器和防火墙不能防这种方法，但是有很多网络出于性能上的考虑，禁止数据包的分片。
　　注意这个选项不能在所有的平台上使用。它在Linux、FreeBSD、OpenBSD以及其它一些UNIX系统能够很好工作。
　　-v
　　冗余模式。强烈推荐使用这个选项，它会给出扫描过程中的详细信息。使用这个选项，你可以得到事半功倍的效果。使用-d选项可以得到更加详细的信息。
　　-h
　　快速参考选项。
　　-oN
　　把扫描结果重定向到一个可读的文件logfilename中。
　　-oM
　　把扫描结果重定向到logfilename文件中，这个文件使用主机可以解析的语法。你可以使用-oM -来代替logfilename，这样输出就被重定向到标准输出stdout。在这种情况下，正常的输出将被覆盖，错误信息荏苒可以输出到标准错误 stderr。要注意，如果同时使用了-v选项，在屏幕上会打印出其它的信息。
　　-oS 　　 thIs l0gz th3 r3suLtS of YouR ScanZ iN a s| 　　THe fiL3 U sPecfy 4s an arGuMEnT! U kAn gIv3 the 4rgument -
　　(wItHOUt qUOteZ) to sh00t output iNT0 stDouT!@!! 莫名其妙，下面是我猜着翻译的，相形字？
　　把扫描结果重定向到一个文件logfilename中，这个文件使用一种"黑客方言"的语法形式(作者开的玩笑?)。同样，使用-oS -就会把结果重定向到标准输出上。
　　-resume
　　某个网络扫描可能由于control-C或者网络损失等原因被中断，使用这个选项可以使扫描接着以前的扫描进行。logfilename是被取消扫描的日志文件，它必须是可读形式或者机器可以解析的形式。而且接着进行的扫描不能增加新的选项，只能使用与被中断的扫描相同的选项。nmap会接着日志文件中的最后一次成功扫描进行新的扫描。
　　-iL
　　从inputfilename文件中读取扫描的目标。在这个文件中要有一个主机或者网络的列表，由空格键、制表键或者回车键作为分割符。如果使用-iL -，nmap就会从标准输入stdin读取主机名字。你可以从指定目标一节得到更加详细的信息。
　　-iR
　　让nmap自己随机挑选主机进行扫描。
　　-p <端口范围>
　　这个选项让你选择要进行扫描的端口号的范围。例如，-p 23表示：只扫描目标主机的23号端口。-p 20-30,139,60000-表示：扫描20到30号端口，139号端口以及所有大于60000的端口。在默认情况下，nmap扫描从1到1024号以及nmap-services文件(如果使用RPM软件包，一般在/usr/share/nmap/目录中)中定义的端口列表。
　　-F
　　快速扫描模式，只扫描在nmap-services文件中列出的端口。显然比扫描所有65535个端口要快。
　　-D
　　使用诱饵扫描方法对目标网络/主机进行扫描。如果nmap使用这种方法对目标网络进行扫描，那么从目标主机/网络的角度来看，扫描就象从其它主机 (decoy1,等)发出的。从而，即使目标主机的IDS(入侵检测系统)对端口扫描发出报警，它们也不可能知道哪个是真正发起扫描的地址，哪个是无辜的。这种扫描方法可以有效地对付例如路由跟踪、response-dropping等积极的防御机制，能够很好地隐藏你的IP地址。
　　每个诱饵主机名使用逗号分割开，你也可以使用ME选项，它代表你自己的主机，和诱饵主机名混杂在一起。如果你把ME放在第六或者更靠后的位置，一些端口扫描检测软件几乎根本不会显示你的IP地址。如果你不使用ME选项，nmap会把你的IP地址随机夹杂在诱饵主机之中。
　　注意:你用来作为诱饵的主机应该正在运行或者你只是偶尔向目标发送SYN数据包。很显然，如果在网络上只有一台主机运行，目标将很轻松就会确定是哪台主机进行的扫描。或许，你还要直接使用诱饵的IP地址而不是其域名，这样诱饵网络的域名服务器的日志上就不会留下关于你的记录。
　　还要注意：一些愚蠢的端口扫描检测软件会拒绝路由试图进行端口扫描的主机。因而，你需要让目标主机和一些诱饵断开连接。如果诱饵是目标主机的网关或者就是其自己时，会给目标主机造成很大问题。所以你需要慎重使用这个选项。
　　诱饵扫描既可以在起始的ping扫描也可以在真正的扫描状态下使用。它也可以和-O选项组合使用。
　　使用太多的诱饵扫描能够减缓你的扫描速度甚至可能造成扫描结果不正确。同时，有些ISP会把你的欺骗包过滤掉。虽然现在大多数的ISP不会对此进行限制。
　　-S
　　在一些情况下，nmap可能无法确定你的源地址(nmap会告诉你)。在这种情况下，可以使用这个选项给出你的IP地址。
　　在欺骗扫描时，也使用这个选项。使用这个选项可以让目标认为是其它的主机对自己进行扫描。
　　-e
　　告诉nmap使用哪个接口发送和接受数据包。nmap能够自动对此接口进行检测，如果无效就会告诉你。
　　-g
　　设置扫描的源端口。一些天真的防火墙和包过滤器的规则集允许源端口为DNS(53)或者FTP-DATA(20)的包通过和实现连接。显然，如果攻击者把源端口修改为20或者53，就可以摧毁防火墙的防护。在使用UDP扫描时，先使用53号端口；使用TCP扫描时，先使用20号端口。注意只有在能够使用这个端口进行扫描时，nmap才会使用这个端口。例如，如果你无法进行TCP扫描，nmap会自动改变源端口，即使你使用了-g选项。
　　对于一些扫描，使用这个选项会造成性能上的微小损失，因为我有时会保存关于特定源端口的一些有用的信息。
　　-r
　　告诉nmap不要打乱被扫描端口的顺序。
　　--randomize_hosts
　　使nmap在扫描之前，打乱每组扫描中的主机顺序，nmap每组可以扫描最多2048台主机。这样，可以使扫描更不容易被网络监视器发现，尤其和--scan_delay 选项组合使用，更能有效避免被发现。
　　-M
　　设置进行TCP connect()扫描时，最多使用多少个套接字进行并行的扫描。使用这个选项可以降低扫描速度，避免远程目标宕机。

4.3 适时选项

　　通常，nmap在运行时，能够很好地根据网络特点进行调整。扫描时，nmap会尽量减少被目标检测到的机会，同时尽可能加快扫描速度。然而，nmap默认的适时策略有时候不太适合你的目标。使用下面这些选项，可以控制nmap的扫描timing：

-T
　　设置nmap的适时策略。Paranoid:为了避开IDS的检测使扫描速度极慢，nmap串行所有的扫描，每隔至少5分钟发送一个包； Sneaky：也差不多，只是数据包的发送间隔是15秒；Polite：不增加太大的网络负载，避免宕掉目标主机，串行每个探测，并且使每个探测有0.4 秒种的间隔；Normal:nmap默认的选项，在不是网络过载或者主机/端口丢失的情况下尽可能快速地扫描；Aggressive:设置5分钟的超时限制，使对每台主机的扫描时间不超过5分钟，并且使对每次探测回应的等待时间不超过1.5秒钟；b>Insane:只适合快速的网络或者你不在意丢失某些信息，每台主机的超时限制是75秒，对每次探测只等待0.3秒钟。你也可是使用数字来代替这些模式，例如：-T 0等于-T Paranoid，-T 5等于-T Insane。
　　这些适时模式不能下面的适时选项组合使用。
--host_timeout
　　设置扫描一台主机的时间，以毫秒为单位。默认的情况下，没有超时限制。
--max_rtt_timeout
　　设置对每次探测的等待时间，以毫秒为单位。如果超过这个时间限制就重传或者超时。默认值是大约9000毫秒。
--min_rtt_timeout
　　当目标主机的响应很快时，nmap就缩短每次探测的超时时间。这样会提高扫描的速度，但是可能丢失某些响应时间比较长的包。使用这个选项，可以让nmap对每次探测至少等待你指定的时间，以毫秒为单位。
--initial_rtt_timeout
　　设置初始探测的超时值。一般这个选项只在使用-P0选项扫描有防火墙保护的主机才有用。默认值是6000毫秒。
--max_parallelism
　　设置最大的并行扫描数量。--max_parallelism 1表示同时只扫描一个端口。这个选项对其它的并行扫描也有效，例如ping sweep, RPC scan。
--scan_delay
　　设置在两次探测之间，nmap必须等待的时间。这个选项主要用于降低网络的负载。

4.4 目标设定

　　在nmap的所有参数中，只有目标参数是必须给出的。其最简单的形式是在命令行直接输入一个主机名或者一个IP地址。如果你希望扫描某个IP地址的一个子网，你可以在主机名或者IP地址的后面加上/掩码。掩码在0(扫描整个网络)到32(只扫描这个主机)。使用/24扫描C类地址，/16扫描B类地址。

　　除此之外，nmap还有更加强大的表示方式让你更加灵活地指定IP地址。例如，如果要扫描这个B类网络128.210.*.*，你可以使用下面三种方式来指定这些地址:128.210.*.*、128.21-.0-255.0-255或者128.210.0.0/16这三种形式是等价的。

5.例子

　　本节将由浅入深地举例说明如何使用nmap。

nmap -v target.example.com
扫描主机target.example.com的所有TCP端口。-v打开冗余模式。

nmap -sS -O target.example.com/24
发起对target.example.com所在网络上的所有255个IP地址的秘密SYN扫描。同时还探测每台主机操作系统的指纹特征。需要root权限。

nmap -sX -p 22,53,110,143,4564 128.210.*.1-127
对B类IP地址128.210中255个可能的8位子网的前半部分发起圣诞树扫描。确定这些系统是否打开了sshd、DNS、pop3d、imapd和4564端口。注意圣诞树扫描对Micro$oft的系统无效，因为其协议栈的TCP层有缺陷。

nmap -v --randomize_hosts -p 80 *.*.2.3-5
只扫描指定的IP范围，有时用于对这个Internet进行取样分析。nmap将寻找Internet上所有后两个字节是.2.3、.2.4、.2.5的 IP地址上的WEB服务器。如果你想发现更多有意思的主机，你可以使用127-222，因为在这个范围内有意思的主机密度更大。

host -l company.com | cut -d -f 4 | ./nmap -v -iL -
列出company.com网络的所有主机，让nmap进行扫描。注意：这项命令在GNU/Linux下使用。如果在其它平台，你可能要使用 其它的命令/选项。

下面是man文档

NMAP(1) Nmap Reference Guide NMAP(1)

NAME

nmap - Network exploration tool and security / port scanner

SYNOPSIS

nmap [Scan Type...] [Options] {target specification}

DESCRIPTION

Nmap (“Network Mapper”) is an open source tool for network exploration

and security auditing. It was designed to rapidly scan large networks,

although it works fine against single hosts. Nmap uses raw IP packets

in novel ways to determine what hosts are available on the network,

what services (application name and version) those hosts are offering,

what operating systems (and OS versions) they are running, what type of

packet filters/firewalls are in use, and dozens of other

characteristics. While Nmap is commonly used for security audits, many

systems and network administrators find it useful for routine tasks

such as network inventory, managing service upgrade schedules, and

monitoring host or service uptime.

The output from Nmap is a list of scanned targets, with supplemental

information on each depending on the options used. Key among that

information is the “interesting ports table”.. That table lists the

port number and protocol, service name, and state. The state is either

open, filtered, closed, or unfiltered. Open. means that an

application on the target machine is listening for connections/packets

on that port. Filtered. means that a firewall, filter, or other

network obstacle is blocking the port so that Nmap cannot tell whether

it is open or closed. Closed. ports have no application listening on

them, though they could open up at any time. Ports are classified as

unfiltered. when they are responsive to Nmap´s probes, but Nmap cannot

determine whether they are open or closed. Nmap reports the state

combinations open|filtered. and closed|filtered. when it cannot

determine which of the two states describe a port. The port table may

also include software version details when version detection has been

requested. When an IP protocol scan is requested (-sO), Nmap provides

information on supported IP protocols rather than listening ports.

In addition to the interesting ports table, Nmap can provide further

information on targets, including reverse DNS names, operating system

guesses, device types, and MAC addresses.

A typical Nmap scan is shown in Example 1. The only Nmap arguments used

in this example are -A, to enable OS and version detection, script

scanning, and traceroute; -T4 for faster execution; and then the two

target hostnames.

Example 1. A representative Nmap scan

# nmap -A -T4 scanme.nmap.org

Starting Nmap ( http://nmap.org )

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 994 filtered ports

PORT STATE SERVICE VERSION

22/tcp open ssh OpenSSH 4.3 (protocol 2.0)

25/tcp closed smtp

53/tcp open domain ISC BIND 9.3.4

70/tcp closed gopher

80/tcp open http Apache httpd 2.2.2 ((Fedora))

|_ HTML title: Go ahead and ScanMe!

113/tcp closed auth

Device type: general purpose

Running: Linux 2.6.X

OS details: Linux 2.6.20-1 (Fedora Core 5)

TRACEROUTE (using port 80/tcp)

HOP RTT ADDRESS

[Cut first seven hops for brevity]

8 10.59 so-4-2-0.mpr3.pao1.us.above.net (64.125.28.142)

9 11.00 metro0.sv.svcolo.com (208.185.168.173)

10 9.93 scanme.nmap.org (64.13.134.52)

Nmap done: 1 IP address (1 host up) scanned in 17.00 seconds

The newest version of Nmap can be obtained from http://nmap.org. The

newest version of this man page is available at

http://nmap.org/book/man.html. It is also included as a chapter of

Nmap Network Scanning: The Official Nmap Project Guide to Network

Discovery and Security Scanning (see http://nmap.org/book/).

OPTIONS SUMMARY

This options summary is printed when Nmap is run with no arguments, and

the latest version is always available at

http://nmap.org/data/nmap.usage.txt. It helps people remember the most

common options, but is no substitute for the in-depth documentation in

the rest of this manual. Some obscure options aren´t even included

here.

Nmap 5.21 ( http://nmap.org )

Usage: nmap [Scan Type(s)] [Options] {target specification}

TARGET SPECIFICATION:

Can pass hostnames, IP addresses, networks, etc.

Ex: scanme.nmap.org, microsoft.com/24, 192.168.0.1; 10.0.0-255.1-254

-iL : Input from list of hosts/networks

-iR : Choose random targets

--exclude : Exclude hosts/networks

--excludefile : Exclude list from file

HOST DISCOVERY:

-sL: List Scan - simply list targets to scan

-sP: Ping Scan - go no further than determining if host is online

-PN: Treat all hosts as online -- skip host discovery

-PS/PA/PU/PY[portlist]: TCP SYN/ACK, UDP or SCTP discovery to given ports

-PE/PP/PM: ICMP echo, timestamp, and netmask request discovery probes

-PO[protocol list]: IP Protocol Ping

-n/-R: Never do DNS resolution/Always resolve [default: sometimes]

--dns-servers : Specify custom DNS servers

--system-dns: Use OS´s DNS resolver

--traceroute: Trace hop path to each host

SCAN TECHNIQUES:

-sS/sT/sA/sW/sM: TCP SYN/Connect()/ACK/Window/Maimon scans

-sU: UDP Scan

-sN/sF/sX: TCP Null, FIN, and Xmas scans

--scanflags : Customize TCP scan flags

-sI : Idle scan

-sY/sZ: SCTP INIT/COOKIE-ECHO scans

-sO: IP protocol scan

-b : FTP bounce scan

PORT SPECIFICATION AND SCAN ORDER:

-p : Only scan specified ports

Ex: -p22; -p1-65535; -p U:53,111,137,T:21-25,80,139,8080

-F: Fast mode - Scan fewer ports than the default scan

-r: Scan ports consecutively - don´t randomize

--top-ports : Scan most common ports

--port-ratio : Scan ports more common than

SERVICE/VERSION DETECTION:

-sV: Probe open ports to determine service/version info

--version-intensity : Set from 0 (light) to 9 (try all probes)

--version-light: Limit to most likely probes (intensity 2)

--version-all: Try every single probe (intensity 9)

--version-trace: Show detailed version scan activity (for debugging)

SCRIPT SCAN:

-sC: equivalent to --script=default

--script=: is a comma separated list of

directories, script-files or script-categories

--script-args=: provide arguments to scripts

--script-trace: Show all data sent and received

--script-updatedb: Update the script database.

OS DETECTION:

-O: Enable OS detection

--osscan-limit: Limit OS detection to promising targets

--osscan-guess: Guess OS more aggressively

TIMING AND PERFORMANCE:

Options which take are in milliseconds, unless you append ´s´

(seconds), ´m´ (minutes), or ´h´ (hours) to the value (e.g. 30m).

-T<0-5>: Set timing template (higher is faster)

--min-hostgroup/max-hostgroup : Parallel host scan group sizes

--min-parallelism/max-parallelism : Probe parallelization

--min-rtt-timeout/max-rtt-timeout/initial-rtt-timeout : Specifies

probe round trip time.

--max-retries : Caps number of port scan probe retransmissions.

--host-timeout : Give up on target after this long

--scan-delay/--max-scan-delay : Adjust delay between probes

--min-rate : Send packets no slower than per second

--max-rate : Send packets no faster than per second

FIREWALL/IDS EVASION AND SPOOFING:

-f; --mtu : fragment packets (optionally w/given MTU)

-D : Cloak a scan with decoys

-S : Spoof source address

-e : Use specified interface

-g/--source-port : Use given port number

--data-length : Append random data to sent packets

--ip-options : Send packets with specified ip options

--ttl : Set IP time-to-live field

--spoof-mac : Spoof your MAC address

--badsum: Send packets with a bogus TCP/UDP/SCTP checksum

--adler32: Use deprecated Adler32 instead of CRC32C for SCTP checksums

OUTPUT:

-oN/-oX/-oS/-oG : Output scan in normal, XML, s|

and Grepable format, respectively, to the given filename.

-oA : Output in the three major formats at once

-v: Increase verbosity level (use twice or more for greater effect)

-d[level]: Set or increase debugging level (Up to 9 is meaningful)

--reason: Display the reason a port is in a particular state

--open: Only show open (or possibly open) ports

--packet-trace: Show all packets sent and received

--iflist: Print host interfaces and routes (for debugging)

--log-errors: Log errors/warnings to the normal-format output file

--append-output: Append to rather than clobber specified output files

--resume : Resume an aborted scan

--stylesheet : XSL stylesheet to transform XML output to HTML

--webxml: Reference stylesheet from Nmap.Org for more portable XML

--no-stylesheet: Prevent associating of XSL stylesheet w/XML output

MISC:

-6: Enable IPv6 scanning

-A: Enables OS detection and Version detection, Script scanning and Traceroute

--datadir : Specify custom Nmap data file location

--send-eth/--send-ip: Send using raw ethernet frames or IP packets

--privileged: Assume that the user is fully privileged

--unprivileged: Assume the user lacks raw socket privileges

-V: Print version number

-h: Print this help summary page.

EXAMPLES:

nmap -v -A scanme.nmap.org

nmap -v -sP 192.168.0.0/16 10.0.0.0/8

nmap -v -iR 10000 -PN -p 80

SEE THE MAN PAGE (http://nmap.org/book/man.html) FOR MORE OPTIONS AND EXAMPLES

TARGET SPECIFICATION

Everything on the Nmap command-line that isn´t an option (or option

argument) is treated as a target host specification. The simplest case

is to specify a target IP address or hostname for scanning.

Sometimes you wish to scan a whole network of adjacent hosts. For this,

Nmap supports CIDR-style. addressing. You can append /numbits to an

IPv4 address or hostname and Nmap will scan every IP address for which

the first numbits are the same as for the reference IP or hostname

given. For example, 192.168.10.0/24 would scan the 256 hosts between

192.168.10.0 (binary: 11000000 10101000 00001010 00000000) and

192.168.10.255 (binary: 11000000 10101000 00001010 11111111),

inclusive. 192.168.10.40/24 would scan exactly the same targets. Given

that the host scanme.nmap.org. is at the IP address 64.13.134.52, the

specification scanme.nmap.org/16 would scan the 65,536 IP addresses

between 64.13.0.0 and 64.13.255.255. The smallest allowed value is /0,

which scans the whole Internet. The largest value is /32, which scans

just the named host or IP address because all address bits are fixed.

CIDR notation is short but not always flexible enough. For example, you

might want to scan 192.168.0.0/16 but skip any IPs ending with .0 or

.255 because they may be used as subnet network and broadcast

addresses. Nmap supports this through octet range addressing. Rather

than specify a normal IP address, you can specify a comma-separated

list of numbers or ranges for each octet. For example,

192.168.0-255.1-254 will skip all addresses in the range that end in .0

or .255, and 192.168.3-5,7.1 will scan the four addresses 192.168.3.1,

192.168.4.1, 192.168.5.1, and 192.168.7.1. Either side of a range may

be omitted; the default values are 0 on the left and 255 on the right.

Using - by itself is the same as 0-255, but remember to use 0- in the

first octet so the target specification doesn´t look like a

command-line option. Ranges need not be limited to the final octets:

the specifier 0-255.0-255.13.37 will perform an Internet-wide scan for

all IP addresses ending in 13.37. This sort of broad sampling can be

useful for Internet surveys and research.

IPv6 addresses can only be specified by their fully qualified IPv6

address or hostname. CIDR and octet ranges aren´t supported for IPv6

because they are rarely useful.

Nmap accepts multiple host specifications on the command line, and they

don´t need to be the same type. The command nmap scanme.nmap.org

192.168.0.0/8 10.0.0,1,3-7.- does what you would expect.

While targets are usually specified on the command lines, the following

options are also available to control target selection:

-iL inputfilename (Input from list) .

Reads target specifications from inputfilename. Passing a huge list

of hosts is often awkward on the command line, yet it is a common

desire. For example, your DHCP server might export a list of 10,000

current leases that you wish to scan. Or maybe you want to scan all

IP addresses except for those to locate hosts using unauthorized

static IP addresses. Simply generate the list of hosts to scan and

pass that filename to Nmap as an argument to the -iL option.

Entries can be in any of the formats accepted by Nmap on the

command line (IP address, hostname, CIDR, IPv6, or octet ranges).

Each entry must be separated by one or more spaces, tabs, or

newlines. You can specify a hyphen (-) as the filename if you want

Nmap to read hosts from standard input rather than an actual file.

The input file may contain comments that start with # and extend to

the end of the line.

-iR num hosts (Choose random targets) .

For Internet-wide surveys and other research, you may want to

choose targets at random. The num hosts argument tells Nmap how

many IPs to generate. Undesirable IPs such as those in certain

private, multicast, or unallocated address ranges are automatically

skipped. The argument 0 can be specified for a never-ending scan.

Keep in mind that some network administrators bristle at

unauthorized scans of their networks and may complain. Use this

option at your own risk! If you find yourself really bored one

rainy afternoon, try the command nmap -sS -PS80 -iR 0 -p 80 to

locate random web servers for browsing.

--exclude host1[,host2[,...]] (Exclude hosts/networks) .

Specifies a comma-separated list of targets to be excluded from the

scan even if they are part of the overall network range you

specify. The list you pass in uses normal Nmap syntax, so it can

include hostnames, CIDR netblocks, octet ranges, etc. This can be

useful when the network you wish to scan includes untouchable

mission-critical servers, systems that are known to react adversely

to port scans, or subnets administered by other people.

--excludefile exclude_file (Exclude list from file) .

This offers the same functionality as the --exclude option, except

that the excluded targets are provided in a newline, space, or tab

delimited exclude_file rather than on the command line.

The exclude file may contain comments that start with # and extend

to the end of the line.

HOST DISCOVERY

One of the very first steps in any network reconnaissance mission is to

reduce a (sometimes huge) set of IP ranges into a list of active or

interesting hosts. Scanning every port of every single IP address is

slow and usually unnecessary. Of course what makes a host interesting

depends greatly on the scan purposes. Network administrators may only

be interested in hosts running a certain service, while security

auditors may care about every single device with an IP address. An

administrator may be comfortable using just an ICMP ping to locate

hosts on his internal network, while an external penetration tester may

use a diverse set of dozens of probes in an attempt to evade firewall

restrictions.

Because host discovery needs are so diverse, Nmap offers a wide variety

of options for customizing the techniques used. Host discovery is

sometimes called ping scan, but it goes well beyond the simple ICMP

echo request packets associated with the ubiquitous ping tool. Users

can skip the ping step entirely with a list scan (-sL) or by disabling

ping (-PN), or engage the network with arbitrary combinations of

multi-port TCP SYN/ACK, UDP, SCTP INIT and ICMP probes. The goal of

these probes is to solicit responses which demonstrate that an IP

address is actually active (is being used by a host or network device).

On many networks, only a small percentage of IP addresses are active at

any given time. This is particularly common with private address space

such as 10.0.0.0/8. That network has 16 million IPs, but I have seen it

used by companies with less than a thousand machines. Host discovery

can find those machines in a sparsely allocated sea of IP addresses.

If no host discovery options are given, Nmap sends an ICMP echo

request, a TCP SYN packet to port 443, and TCP ACK packet to port 80,

and an ICMP timestamp request. These defaults are equivalent to the -PE

-PS443 -PA80 -PP options. An exception to this is that an ARP scan is

used for any targets which are on a local ethernet network. For

unprivileged Unix shell users, the default probes are a SYN packet to

ports 80 and 443 using the connect system call.. This host discovery

is often sufficient when scanning local networks, but a more

comprehensive set of discovery probes is recommended for security

auditing.

The -P* options (which select ping types) can be combined. You can

increase your odds of penetrating strict firewalls by sending many

probe types using different TCP ports/flags and ICMP codes. Also note

that ARP discovery (-PR). is done by default against targets on a

local ethernet network even if you specify other -P* options, because

it is almost always faster and more effective.

By default, Nmap does host discovery and then performs a port scan

against each host it determines is online. This is true even if you

specify non-default host discovery types such as UDP probes (-PU). Read

about the -sP option to learn how to perform only host discovery, or

use -PN to skip host discovery and port scan all target hosts. The

following options control host discovery:

-sL (List Scan) .

The list scan is a degenerate form of host discovery that simply

lists each host of the network(s) specified, without sending any

packets to the target hosts. By default, Nmap still does

reverse-DNS resolution on the hosts to learn their names. It is

often surprising how much useful information simple hostnames give

out. For example, fw.chi is the name of one company´s Chicago

firewall. Nmap also reports the total number of IP addresses at

the end. The list scan is a good sanity check to ensure that you

have proper IP addresses for your targets. If the hosts sport

domain names you do not recognize, it is worth investigating

further to prevent scanning the wrong company´s network.

Since the idea is to simply print a list of target hosts, options

for higher level functionality such as port scanning, OS detection,

or ping scanning cannot be combined with this. If you wish to

disable ping scanning while still performing such higher level

functionality, read up on the -PN (skip ping) option.

-sP (Skip port scan) .

This option tells Nmap not to do a port scan after host discovery,

and only print out the available hosts that responded to the scan.

This is often known as a “ping scan”, but you can also request that

traceroute and NSE host scripts be run. This is by default one step

more intrusive than the list scan, and can often be used for the

same purposes. It allows light reconnaissance of a target network

without attracting much attention. Knowing how many hosts are up is

more valuable to attackers than the list provided by list scan of

every single IP and host name.

Systems administrators often find this option valuable as well. It

can easily be used to count available machines on a network or

monitor server availability. This is often called a ping sweep, and

is more reliable than pinging the broadcast address because many

hosts do not reply to broadcast queries.

The -sP option sends an ICMP echo request, TCP SYN to port 443, TCP

ACK to port 80, and an ICMP timestamp request by default. When

executed by an unprivileged user, only SYN packets are sent (using

a connect call) to ports 80 and 443 on the target. When a

privileged user tries to scan targets on a local ethernet network,

ARP requests are used unless --send-ip was specified. The -sP

option can be combined with any of the discovery probe types (the

-P* options, excluding -PN) for greater flexibility. If any of

those probe type and port number options are used, the default

probes are overridden. When strict firewalls are in place between

the source host running Nmap and the target network, using those

advanced techniques is recommended. Otherwise hosts could be missed

when the firewall drops probes or their responses.

-PN (No ping) .

This option skips the Nmap discovery stage altogether. Normally,

Nmap uses this stage to determine active machines for heavier

scanning. By default, Nmap only performs heavy probing such as port

scans, version detection, or OS detection against hosts that are

found to be up. Disabling host discovery with -PN causes Nmap to

attempt the requested scanning functions against every target IP

address specified. So if a class B sized target address space (/16)

is specified on the command line, all 65,536 IP addresses are

scanned. Proper host discovery is skipped as with the list scan,

but instead of stopping and printing the target list, Nmap

continues to perform requested functions as if each target IP is

active. To skip ping scan and port scan, while still allowing NSE

to run, use the two options -PN -sP together.

For machines on a local ethernet network, ARP scanning will still

be performed (unless --send-ip is specified) because Nmap needs MAC

addresses to further scan target hosts. This option flag used to be

P0 (uses zero), but was renamed to avoid confusion with protocol

ping´s PO (uses the letter O) flag.

-PS port list (TCP SYN Ping) .

This option sends an empty TCP packet with the SYN flag set. The

default destination port is 80 (configurable at compile time by

changing DEFAULT_TCP_PROBE_PORT_SPEC in nmap.h). Alternate ports

can be specified as a parameter. The syntax is the same as for the

-p except that port type specifiers like T: are not allowed.

Examples are -PS22 and -PS22-25,80,113,1050,35000. Note that there

can be no space between -PS and the port list. If multiple probes

are specified they will be sent in parallel.

The SYN flag suggests to the remote system that you are attempting

to establish a connection. Normally the destination port will be

closed, and a RST (reset) packet sent back. If the port happens to

be open, the target will take the second step of a TCP

three-way-handshake. by responding with a SYN/ACK TCP packet. The

machine running Nmap then tears down the nascent connection by

responding with a RST rather than sending an ACK packet which would

complete the three-way-handshake and establish a full connection.

The RST packet is sent by the kernel of the machine running Nmap in

response to the unexpected SYN/ACK, not by Nmap itself.

Nmap does not care whether the port is open or closed. Either the

RST or SYN/ACK response discussed previously tell Nmap that the

host is available and responsive.

On Unix boxes, only the privileged user root. is generally able to

send and receive raw TCP packets.. For unprivileged users, a

workaround is automatically employed. whereby the connect system

call is initiated against each target port. This has the effect of

sending a SYN packet to the target host, in an attempt to establish

a connection. If connect returns with a quick success or an

ECONNREFUSED failure, the underlying TCP stack must have received a

SYN/ACK or RST and the host is marked available. If the connection

attempt is left hanging until a timeout is reached, the host is

marked as down. This workaround is also used for IPv6 connections,

as raw IPv6 packet building support is not yet available in Nmap..

-PA port list (TCP ACK Ping) .

The TCP ACK ping is quite similar to the just-discussed SYN ping.

The difference, as you could likely guess, is that the TCP ACK flag

is set instead of the SYN flag. Such an ACK packet purports to be

acknowledging data over an established TCP connection, but no such

connection exists. So remote hosts should always respond with a RST

packet, disclosing their existence in the process.

The -PA option uses the same default port as the SYN probe (80) and

can also take a list of destination ports in the same format. If an

unprivileged user tries this, or an IPv6 target is specified, the

connect workaround discussed previously is used. This workaround is

imperfect because connect is actually sending a SYN packet rather

than an ACK.

The reason for offering both SYN and ACK ping probes is to maximize

the chances of bypassing firewalls. Many administrators configure

routers and other simple firewalls to block incoming SYN packets

except for those destined for public services like the company web

site or mail server. This prevents other incoming connections to

the organization, while allowing users to make unobstructed

outgoing connections to the Internet. This non-stateful approach

takes up few resources on the firewall/router and is widely

supported by hardware and software filters. The Linux

Netfilter/iptables. firewall software offers the --syn convenience

option to implement this stateless approach. When stateless

firewall rules such as this are in place, SYN ping probes (-PS) are

likely to be blocked when sent to closed target ports. In such

cases, the ACK probe shines as it cuts right through these rules.

Another common type of firewall uses stateful rules that drop

unexpected packets. This feature was initially found mostly on

high-end firewalls, though it has become much more common over the

years. The Linux Netfilter/iptables system supports this through

the --state option, which categorizes packets based on connection

state. A SYN probe is more likely to work against such a system, as

unexpected ACK packets are generally recognized as bogus and

dropped. A solution to this quandary is to send both SYN and ACK

probes by specifying -PS and -PA.

-PU port list (UDP Ping) .

Another host discovery option is the UDP ping, which sends a UDP

packet to the given ports. For most ports, the packet will be

empty, though for a few a protocol-specific payload will be sent

that is more likely to get a response.. See the file payload.cc.

for exactly which ports have payloads. The --data-length. option

sends a fixed-length random payload for all ports.

The port list takes the same format as with the previously

discussed -PS and -PA options. If no ports are specified, the

default is 40125. This default can be configured at compile-time by

changing DEFAULT_UDP_PROBE_PORT_SPEC. in nmap.h.. A highly

uncommon port is used by default because sending to open ports is

often undesirable for this particular scan type.

Upon hitting a closed port on the target machine, the UDP probe

should elicit an ICMP port unreachable packet in return. This

signifies to Nmap that the machine is up and available. Many other

types of ICMP errors, such as host/network unreachables or TTL

exceeded are indicative of a down or unreachable host. A lack of

response is also interpreted this way. If an open port is reached,

most services simply ignore the empty packet and fail to return any

response. This is why the default probe port is 40125, which is

highly unlikely to be in use. A few services, such as the Character

Generator (chargen) protocol, will respond to an empty UDP packet,

and thus disclose to Nmap that the machine is available.

The primary advantage of this scan type is that it bypasses

firewalls and filters that only screen TCP. For example, I once

owned a Linksys BEFW11S4 wireless broadband router. The external

interface of this device filtered all TCP ports by default, but UDP

probes would still elicit port unreachable messages and thus give

away the device.

-PY port list (SCTP INIT Ping) .

This option sends an SCTP packet containing a minimal INIT chunk.

The default destination port is 80 (configurable at compile time by

changing DEFAULT_SCTP_PROBE_PORT_SPEC in nmap.h). Alternate ports

can be specified as a parameter. The syntax is the same as for the

-p except that port type specifiers like S: are not allowed.

Examples are -PY22 and -PY22,80,179,5060. Note that there can be no

space between -PY and the port list. If multiple probes are

specified they will be sent in parallel.

The INIT chunk suggests to the remote system that you are

attempting to establish an association. Normally the destination

port will be closed, and an ABORT chunk will be sent back. If the

port happens to be open, the target will take the second step of an

SCTP four-way-handshake. by responding with an INIT-ACK chunk. If

the machine running Nmap has a functional SCTP stack, then it tears

down the nascent association by responding with an ABORT chunk

rather than sending a COOKIE-ECHO chunk which would be the next

step in the four-way-handshake. The ABORT packet is sent by the

kernel of the machine running Nmap in response to the unexpected

INIT-ACK, not by Nmap itself.

Nmap does not care whether the port is open or closed. Either the

ABORT or INIT-ACK response discussed previously tell Nmap that the

host is available and responsive.

On Unix boxes, only the privileged user root. is generally able to

send and receive raw SCTP packets.. Using SCTP INIT Pings is

currently not possible for unprivileged users.. The same

limitation applies to IPv6, which is currently not supported for

SCTP INIT Ping..

-PE; -PP; -PM (ICMP Ping Types) .

In addition to the unusual TCP, UDP and SCTP host discovery types

discussed previously, Nmap can send the standard packets sent by

the ubiquitous ping program. Nmap sends an ICMP type 8 (echo

request) packet to the target IP addresses, expecting a type 0

(echo reply) in return from available hosts.. Unfortunately for

network explorers, many hosts and firewalls now block these

packets, rather than responding as required by RFC 1122[2]. For

this reason, ICMP-only scans are rarely reliable enough against

unknown targets over the Internet. But for system administrators

monitoring an internal network, they can be a practical and

efficient approach. Use the -PE option to enable this echo request

behavior.

While echo request is the standard ICMP ping query, Nmap does not

stop there. The ICMP standards (RFC 792[3]. and RFC 950[4]. “a

host SHOULD NOT implement these messages”. Timestamp and address

mask queries can be sent with the -PP and -PM options,

respectively. A timestamp reply (ICMP code 14) or address mask

reply (code 18) discloses that the host is available. These two

queries can be valuable when administrators specifically block echo

request packets while forgetting that other ICMP queries can be

used for the same purpose.

-PO protocol list (IP Protocol Ping) .

The newest host discovery option is the IP protocol ping, which

sends IP packets with the specified protocol number set in their IP

header. The protocol list takes the same format as do port lists in

the previously discussed TCP, UDP and SCTP host discovery options.

If no protocols are specified, the default is to send multiple IP

packets for ICMP (protocol 1), IGMP (protocol 2), and IP-in-IP

(protocol 4). The default protocols can be configured at

compile-time by changing DEFAULT_PROTO_PROBE_PORT_SPEC. in nmap.h.

Note that for the ICMP, IGMP, TCP (protocol 6), UDP (protocol 17)

and SCTP (protocol 132), the packets are sent with the proper

protocol headers. while other protocols are sent with no

additional data beyond the IP header (unless the --data-length.

option is specified).

This host discovery method looks for either responses using the

same protocol as a probe, or ICMP protocol unreachable messages

which signify that the given protocol isn´t supported on the

destination host. Either type of response signifies that the target

host is alive.

-PR (ARP Ping) .

One of the most common Nmap usage scenarios is to scan an ethernet

LAN. On most LANs, especially those using private address ranges

specified by RFC 1918[5], the vast majority of IP addresses are

unused at any given time. When Nmap tries to send a raw IP packet

such as an ICMP echo request, the operating system must determine

the destination hardware (ARP) address corresponding to the target

IP so that it can properly address the ethernet frame. This is

often slow and problematic, since operating systems weren´t written

with the expectation that they would need to do millions of ARP

requests against unavailable hosts in a short time period.

ARP scan puts Nmap and its optimized algorithms in charge of ARP

requests. And if it gets a response back, Nmap doesn´t even need to

worry about the IP-based ping packets since it already knows the

host is up. This makes ARP scan much faster and more reliable than

IP-based scans. So it is done by default when scanning ethernet

hosts that Nmap detects are on a local ethernet network. Even if

different ping types (such as -PE or -PS) are specified, Nmap uses

ARP instead for any of the targets which are on the same LAN. If

you absolutely don´t want to do an ARP scan, specify --send-ip.

--traceroute (Trace path to host) .

Traceroutes are performed post-scan using information from the scan

results to determine the port and protocol most likely to reach the

target. It works with all scan types except connect scans (-sT) and

idle scans (-sI). All traces use Nmap´s dynamic timing model and

are performed in parallel.

Traceroute works by sending packets with a low TTL (time-to-live)

in an attempt to elicit ICMP Time Exceeded messages from

intermediate hops between the scanner and the target host. Standard

traceroute implementations start with a TTL of 1 and increment the

TTL until the destination host is reached. Nmap´s traceroute starts

with a high TTL and then decrements the TTL until it reaches zero.

Doing it backwards lets Nmap employ clever caching algorithms to

speed up traces over multiple hosts. On average Nmap sends 5–10

fewer packets per host, depending on network conditions. If a

single subnet is being scanned (i.e. 192.168.0.0/24) Nmap may only

have to send a single packet to most hosts.

-n (No DNS resolution) .

Tells Nmap to never do reverse DNS resolution on the active IP

addresses it finds. Since DNS can be slow even with Nmap´s built-in

parallel stub resolver, this option can slash scanning times.

-R (DNS resolution for all targets) .

Tells Nmap to always do reverse DNS resolution on the target IP

addresses. Normally reverse DNS is only performed against

responsive (online) hosts.

--system-dns (Use system DNS resolver) .

By default, Nmap resolves IP addresses by sending queries directly

to the name servers configured on your host and then listening for

responses. Many requests (often dozens) are performed in parallel

to improve performance. Specify this option to use your system

resolver instead (one IP at a time via the getnameinfo call). This

is slower and rarely useful unless you find a bug in the Nmap

parallel resolver (please let us know if you do). The system

resolver is always used for IPv6 scans.

--dns-servers server1[,server2[,...]] (Servers to use for reverse DNS

queries) .

By default, Nmap determines your DNS servers (for rDNS resolution)

from your resolv.conf file (Unix) or the Registry (Win32).

Alternatively, you may use this option to specify alternate

servers. This option is not honored if you are using --system-dns

or an IPv6 scan. Using multiple DNS servers is often faster,

especially if you choose authoritative servers for your target IP

space. This option can also improve stealth, as your requests can

be bounced off just about any recursive DNS server on the Internet.

This option also comes in handy when scanning private networks.

Sometimes only a few name servers provide proper rDNS information,

and you may not even know where they are. You can scan the network

for port 53 (perhaps with version detection), then try Nmap list

scans (-sL) specifying each name server one at a time with

--dns-servers until you find one which works.

PORT SCANNING BASICS

While Nmap has grown in functionality over the years, it began as an

efficient port scanner, and that remains its core function. The simple

command nmap target scans more than 1660 TCP ports on the host target.

While many port scanners have traditionally lumped all ports into the

open or closed states, Nmap is much more granular. It divides ports

into six states: open, closed, filtered, unfiltered, open|filtered, or

closed|filtered.

These states are not intrinsic properties of the port itself, but

describe how Nmap sees them. For example, an Nmap scan from the same

network as the target may show port 135/tcp as open, while a scan at

the same time with the same options from across the Internet might show

that port as filtered.

The six port states recognized by Nmap

An application is actively accepting TCP connections, UDP datagrams

or SCTP associations on this port. Finding these is often the

primary goal of port scanning. Security-minded people know that

each open port is an avenue for attack. Attackers and pen-testers

want to exploit the open ports, while administrators try to close

or protect them with firewalls without thwarting legitimate users.

Open ports are also interesting for non-security scans because they

show services available for use on the network.

A closed port is accessible (it receives and responds to Nmap probe

packets), but there is no application listening on it. They can be

helpful in showing that a host is up on an IP address (host

discovery, or ping scanning), and as part of OS detection. Because

closed ports are reachable, it may be worth scanning later in case

some open up. Administrators may want to consider blocking such

ports with a firewall. Then they would appear in the filtered

state, discussed next.

Nmap cannot determine whether the port is open because packet

filtering prevents its probes from reaching the port. The filtering

could be from a dedicated firewall device, router rules, or

host-based firewall software. These ports frustrate attackers

because they provide so little information. Sometimes they respond

with ICMP error messages such as type 3 code 13 (destination

unreachable: communication administratively prohibited), but

filters that simply drop probes without responding are far more

common. This forces Nmap to retry several times just in case the

probe was dropped due to network congestion rather than filtering.

This slows down the scan dramatically.

The unfiltered state means that a port is accessible, but Nmap is

unable to determine whether it is open or closed. Only the ACK

scan, which is used to map firewall rulesets, classifies ports into

this state. Scanning unfiltered ports with other scan types such as

Window scan, SYN scan, or FIN scan, may help resolve whether the

port is open.

Nmap places ports in this state when it is unable to determine

whether a port is open or filtered. This occurs for scan types in

which open ports give no response. The lack of response could also

mean that a packet filter dropped the probe or any response it

elicited. So Nmap does not know for sure whether the port is open

or being filtered. The UDP, IP protocol, FIN, NULL, and Xmas scans

classify ports this way.

This state is used when Nmap is unable to determine whether a port

is closed or filtered. It is only used for the IP ID idle scan.

PORT SCANNING TECHNIQUES

As a novice performing automotive repair, I can struggle for hours

trying to fit my rudimentary tools (hammer, duct tape, wrench, etc.) to

the task at hand. When I fail miserably and tow my jalopy to a real

mechanic, he invariably fishes around in a huge tool chest until

pulling out the perfect gizmo which makes the job seem effortless. The

art of port scanning is similar. Experts understand the dozens of scan

techniques and choose the appropriate one (or combination) for a given

task. Inexperienced users and script kiddies,. on the other hand, try

to solve every problem with the default SYN scan. Since Nmap is free,

the only barrier to port scanning mastery is knowledge. That certainly

beats the automotive world, where it may take great skill to determine

that you need a strut spring compressor, then you still have to pay

thousands of dollars for it.

Most of the scan types are only available to privileged users.. This

is because they send and receive raw packets,. which requires root

access on Unix systems. Using an administrator account on Windows is

recommended, though Nmap sometimes works for unprivileged users on that

platform when WinPcap has already been loaded into the OS. Requiring

root privileges was a serious limitation when Nmap was released in

1997, as many users only had access to shared shell accounts. Now, the

world is different. Computers are cheaper, far more people have

always-on direct Internet access, and desktop Unix systems (including

Linux and Mac OS X) are prevalent. A Windows version of Nmap is now

available, allowing it to run on even more desktops. For all these

reasons, users have less need to run Nmap from limited shared shell

accounts. This is fortunate, as the privileged options make Nmap far

more powerful and flexible.

While Nmap attempts to produce accurate results, keep in mind that all

of its insights are based on packets returned by the target machines

(or firewalls in front of them). Such hosts may be untrustworthy and

send responses intended to confuse or mislead Nmap. Much more common

are non-RFC-compliant hosts that do not respond as they should to Nmap

probes. FIN, NULL, and Xmas scans are particularly susceptible to this

problem. Such issues are specific to certain scan types and so are

discussed in the individual scan type entries.

This section documents the dozen or so port scan techniques supported

by Nmap. Only one method may be used at a time, except that UDP scan

(-sU) and any one of the SCTP scan types (-sY, -sZ) may be combined

with any one of the TCP scan types. As a memory aid, port scan type

options are of the form -sC, where C is a prominent character in the

scan name, usually the first. The one exception to this is the

deprecated FTP bounce scan (-b). By default, Nmap performs a SYN Scan,

though it substitutes a connect scan if the user does not have proper

privileges to send raw packets (requires root access on Unix) or if

IPv6 targets were specified. Of the scans listed in this section,

unprivileged users can only execute connect and FTP bounce scans.

-sS (TCP SYN scan) .

SYN scan is the default and most popular scan option for good

reasons. It can be performed quickly, scanning thousands of ports

per second on a fast network not hampered by restrictive firewalls.

SYN scan is relatively unobtrusive and stealthy, since it never

completes TCP connections. It also works against any compliant TCP

stack rather than depending on idiosyncrasies of specific platforms

as Nmap´s FIN/NULL/Xmas, Maimon and idle scans do. It also allows

clear, reliable differentiation between the open, closed, and

filtered states.

This technique is often referred to as half-open scanning, because

you don´t open a full TCP connection. You send a SYN packet, as if

you are going to open a real connection and then wait for a

response. A SYN/ACK indicates the port is listening (open), while a

RST (reset) is indicative of a non-listener. If no response is

received after several retransmissions, the port is marked as

filtered. The port is also marked filtered if an ICMP unreachable

error (type 3, code 1, 2, 3, 9, 10, or 13) is received.

-sT (TCP connect scan) .

TCP connect scan is the default TCP scan type when SYN scan is not

an option. This is the case when a user does not have raw packet

privileges or is scanning IPv6 networks. Instead of writing raw

packets as most other scan types do, Nmap asks the underlying

operating system to establish a connection with the target machine

and port by issuing the connect system call. This is the same

high-level system call that web browsers, P2P clients, and most

other network-enabled applications use to establish a connection.

It is part of a programming interface known as the Berkeley Sockets

API. Rather than read raw packet responses off the wire, Nmap uses

this API to obtain status information on each connection attempt.

When SYN scan is available, it is usually a better choice. Nmap has

less control over the high level connect call than with raw

packets, making it less efficient. The system call completes

connections to open target ports rather than performing the

half-open reset that SYN scan does. Not only does this take longer

and require more packets to obtain the same information, but target

machines are more likely to log the connection. A decent IDS will

catch either, but most machines have no such alarm system. Many

services on your average Unix system will add a note to syslog, and

sometimes a cryptic error message, when Nmap connects and then

closes the connection without sending data. Truly pathetic services

crash when this happens, though that is uncommon. An administrator

who sees a bunch of connection attempts in her logs from a single

system should know that she has been connect scanned.

-sU (UDP scans) .

While most popular services on the Internet run over the TCP

protocol, UDP[6] services are widely deployed. DNS, SNMP, and DHCP

(registered ports 53, 161/162, and 67/68) are three of the most

common. Because UDP scanning is generally slower and more difficult

than TCP, some security auditors ignore these ports. This is a

mistake, as exploitable UDP services are quite common and attackers

certainly don´t ignore the whole protocol. Fortunately, Nmap can

help inventory UDP ports.

UDP scan is activated with the -sU option. It can be combined with

a TCP scan type such as SYN scan (-sS) to check both protocols

during the same run.

UDP scan works by sending a UDP packet to every targeted port. For

some common ports such as 53 and 161, a protocol-specific payload

is sent, but for most ports the packet is empty.. The

--data-length option can be used to send a fixed-length random

payload to every port. If an ICMP port unreachable error (type 3,

code 3) is returned, the port is closed. Other ICMP unreachable

errors (type 3, codes 1, 2, 9, 10, or 13) mark the port as

filtered. Occasionally, a service will respond with a UDP packet,

proving that it is open. If no response is received after

retransmissions, the port is classified as open|filtered. This

means that the port could be open, or perhaps packet filters are

blocking the communication. Version detection (-sV) can be used to

help differentiate the truly open ports from the filtered ones.

A big challenge with UDP scanning is doing it quickly. Open and

filtered ports rarely send any response, leaving Nmap to time out

and then conduct retransmissions just in case the probe or response

were lost. Closed ports are often an even bigger problem. They

usually send back an ICMP port unreachable error. But unlike the

RST packets sent by closed TCP ports in response to a SYN or

connect scan, many hosts rate limit. ICMP port unreachable

messages by default. Linux and Solaris are particularly strict

about this. For example, the Linux 2.4.20 kernel limits destination

unreachable messages to one per second (in net/ipv4/icmp.c).

Nmap detects rate limiting and slows down accordingly to avoid

flooding the network with useless packets that the target machine

will drop. Unfortunately, a Linux-style limit of one packet per

second makes a 65,536-port scan take more than 18 hours. Ideas for

speeding your UDP scans up include scanning more hosts in parallel,

doing a quick scan of just the popular ports first, scanning from

behind the firewall, and using --host-timeout to skip slow hosts.

-sY (SCTP INIT scan) .

SCTP[7] is a relatively new alternative to the TCP and UDP

protocols, combining most characteristics of TCP and UDP, and also

adding new features like multi-homing and multi-streaming. It is

mostly being used for SS7/SIGTRAN related services but has the

potential to be used for other applications as well. SCTP INIT scan

is the SCTP equivalent of a TCP SYN scan. It can be performed

quickly, scanning thousands of ports per second on a fast network

not hampered by restrictive firewalls. Like SYN scan, INIT scan is

relatively unobtrusive and stealthy, since it never completes SCTP

associations. It also allows clear, reliable differentiation

between the open, closed, and filtered states.

This technique is often referred to as half-open scanning, because

you don´t open a full SCTP association. You send an INIT chunk, as

if you are going to open a real association and then wait for a

response. An INIT-ACK chunk indicates the port is listening (open),

while an ABORT chunk is indicative of a non-listener. If no

response is received after several retransmissions, the port is

marked as filtered. The port is also marked filtered if an ICMP

unreachable error (type 3, code 1, 2, 3, 9, 10, or 13) is received.

-sN; -sF; -sX (TCP NULL, FIN, and Xmas scans) .

These three scan types (even more are possible with the --scanflags

option described in the next section) exploit a subtle loophole in

the TCP RFC[8] to differentiate between open and closed ports. Page

65 of RFC 793 says that “if the [destination] port state is CLOSED

.... an incoming segment not containing a RST causes a RST to be

sent in response.” Then the next page discusses packets sent to

open ports without the SYN, RST, or ACK bits set, stating that:

“you are unlikely to get here, but if you do, drop the segment, and

return.”

When scanning systems compliant with this RFC text, any packet not

containing SYN, RST, or ACK bits will result in a returned RST if

the port is closed and no response at all if the port is open. As

long as none of those three bits are included, any combination of

the other three (FIN, PSH, and URG) are OK. Nmap exploits this with

three scan types:

Null scan (-sN)

Does not set any bits (TCP flag header is 0)

FIN scan (-sF)

Sets just the TCP FIN bit.

Xmas scan (-sX)

Sets the FIN, PSH, and URG flags, lighting the packet up like a

Christmas tree.

These three scan types are exactly the same in behavior except for

the TCP flags set in probe packets. If a RST packet is received,

the port is considered closed, while no response means it is

open|filtered. The port is marked filtered if an ICMP unreachable

error (type 3, code 1, 2, 3, 9, 10, or 13) is received.

The key advantage to these scan types is that they can sneak

through certain non-stateful firewalls and packet filtering

routers. Another advantage is that these scan types are a little

more stealthy than even a SYN scan. Don´t count on this though—most

modern IDS products can be configured to detect them. The big

downside is that not all systems follow RFC 793 to the letter. A

number of systems send RST responses to the probes regardless of

whether the port is open or not. This causes all of the ports to be

labeled closed. Major operating systems that do this are Microsoft

Windows, many Cisco devices, BSDI, and IBM OS/400. This scan does

work against most Unix-based systems though. Another downside of

these scans is that they can´t distinguish open ports from certain

filtered ones, leaving you with the response open|filtered.

-sA (TCP ACK scan) .

This scan is different than the others discussed so far in that it

never determines open (or even open|filtered) ports. It is used to

map out firewall rulesets, determining whether they are stateful or

not and which ports are filtered.

The ACK scan probe packet has only the ACK flag set (unless you use

--scanflags). When scanning unfiltered systems, open and closed

ports will both return a RST packet. Nmap then labels them as

unfiltered, meaning that they are reachable by the ACK packet, but

whether they are open or closed is undetermined. Ports that don´t

respond, or send certain ICMP error messages back (type 3, code 1,

2, 3, 9, 10, or 13), are labeled filtered.

-sW (TCP Window scan) .

Window scan is exactly the same as ACK scan except that it exploits

an implementation detail of certain systems to differentiate open

ports from closed ones, rather than always printing unfiltered when

a RST is returned. It does this by examining the TCP Window field

of the RST packets returned. On some systems, open ports use a

positive window size (even for RST packets) while closed ones have

a zero window. So instead of always listing a port as unfiltered

when it receives a RST back, Window scan lists the port as open or

closed if the TCP Window value in that reset is positive or zero,

respectively.

This scan relies on an implementation detail of a minority of

systems out on the Internet, so you can´t always trust it. Systems

that don´t support it will usually return all ports closed. Of

course, it is possible that the machine really has no open ports.

If most scanned ports are closed but a few common port numbers

(such as 22, 25, 53) are filtered, the system is most likely

susceptible. Occasionally, systems will even show the exact

opposite behavior. If your scan shows 1000 open ports and three

closed or filtered ports, then those three may very well be the

truly open ones.

-sM (TCP Maimon scan) .

The Maimon scan is named after its discoverer, Uriel Maimon.. He

described the technique in Phrack Magazine issue #49 (November

1996).. Nmap, which included this technique, was released two

issues later. This technique is exactly the same as NULL, FIN, and

Xmas scans, except that the probe is FIN/ACK. According to RFC

793[8] (TCP), a RST packet should be generated in response to such

a probe whether the port is open or closed. However, Uriel noticed

that many BSD-derived systems simply drop the packet if the port is

open.

--scanflags (Custom TCP scan) .

Truly advanced Nmap users need not limit themselves to the canned

scan types offered. The --scanflags option allows you to design

your own scan by specifying arbitrary TCP flags.. Let your

creative juices flow, while evading intrusion detection systems.

whose vendors simply paged through the Nmap man page adding

specific rules!

The --scanflags argument can be a numerical flag value such as 9

(PSH and FIN), but using symbolic names is easier. Just mash

together any combination of URG, ACK, PSH, RST, SYN, and FIN. For

example, --scanflags URGACKPSHRSTSYNFIN sets everything, though

it´s not very useful for scanning. The order these are specified in

is irrelevant.

In addition to specifying the desired flags, you can specify a TCP

scan type (such as -sA or -sF). That base type tells Nmap how to

interpret responses. For example, a SYN scan considers no-response

to indicate a filtered port, while a FIN scan treats the same as

open|filtered. Nmap will behave the same way it does for the base

scan type, except that it will use the TCP flags you specify

instead. If you don´t specify a base type, SYN scan is used.

-sZ (SCTP COOKIE ECHO scan) .

SCTP COOKIE ECHO scan is a more advanced SCTP scan. It takes

advantage of the fact that SCTP implementations should silently

drop packets containing COOKIE ECHO chunks on open ports, but send

an ABORT if the port is closed. The advantage of this scan type is

that it is not as obvious a port scan than an INIT scan. Also,

there may be non-stateful firewall rulesets blocking INIT chunks,

but not COOKIE ECHO chunks. Don´t be fooled into thinking that this

will make a port scan invisible; a good IDS will be able to detect

SCTP COOKIE ECHO scans too. The downside is that SCTP COOKIE ECHO

scans cannot differentiate between open and filtered ports, leaving

you with the state open|filtered in both cases.

-sI zombie host[:probeport] (idle scan) .

This advanced scan method allows for a truly blind TCP port scan of

the target (meaning no packets are sent to the target from your

real IP address). Instead, a unique side-channel attack exploits

predictable IP fragmentation ID sequence generation on the zombie

host to glean information about the open ports on the target. IDS

systems will display the scan as coming from the zombie machine you

specify (which must be up and meet certain criteria). This

fascinating scan type is too complex to fully describe in this

reference guide, so I wrote and posted an informal paper with full

details at http://nmap.org/book/idlescan.html.

Besides being extraordinarily stealthy (due to its blind nature),

this scan type permits mapping out IP-based trust relationships

between machines. The port listing shows open ports from the

perspective of the zombie host. So you can try scanning a target

using various zombies that you think might be trusted. (via

router/packet filter rules).

You can add a colon followed by a port number to the zombie host if

you wish to probe a particular port on the zombie for IP ID

changes. Otherwise Nmap will use the port it uses by default for

TCP pings (80).

-sO (IP protocol scan) .

IP protocol scan allows you to determine which IP protocols (TCP,

ICMP, IGMP, etc.) are supported by target machines. This isn´t

technically a port scan, since it cycles through IP protocol

numbers rather than TCP or UDP port numbers. Yet it still uses the

-p option to select scanned protocol numbers, reports its results

within the normal port table format, and even uses the same

underlying scan engine as the true port scanning methods. So it is

close enough to a port scan that it belongs here.

Besides being useful in its own right, protocol scan demonstrates

the power of open-source software. While the fundamental idea is

pretty simple, I had not thought to add it nor received any

requests for such functionality. Then in the summer of 2000,

Gerhard Rieger. conceived the idea, wrote an excellent patch

implementing it, and sent it to the nmap-hackers mailing list.. I

incorporated that patch into the Nmap tree and released a new

version the next day. Few pieces of commercial software have users

enthusiastic enough to design and contribute their own

improvements!

Protocol scan works in a similar fashion to UDP scan. Instead of

iterating through the port number field of a UDP packet, it sends

IP packet headers and iterates through the eight-bit IP protocol

field. The headers are usually empty, containing no data and not

even the proper header for the claimed protocol. The exceptions are

TCP, UDP, ICMP, SCTP, and IGMP. A proper protocol header for those

is included since some systems won´t send them otherwise and

because Nmap already has functions to create them. Instead of

watching for ICMP port unreachable messages, protocol scan is on

the lookout for ICMP protocol unreachable messages. If Nmap

receives any response in any protocol from the target host, Nmap

marks that protocol as open. An ICMP protocol unreachable error

(type 3, code 2) causes the protocol to be marked as closed Other

ICMP unreachable errors (type 3, code 1, 3, 9, 10, or 13) cause the

protocol to be marked filtered (though they prove that ICMP is open

at the same time). If no response is received after

retransmissions, the protocol is marked open|filtered

-b FTP relay host (FTP bounce scan) .

An interesting feature of the FTP protocol (RFC 959[9]) is support

for so-called proxy FTP connections. This allows a user to connect

to one FTP server, then ask that files be sent to a third-party

server. Such a feature is ripe for abuse on many levels, so most

servers have ceased supporting it. One of the abuses this feature

allows is causing the FTP server to port scan other hosts. Simply

ask the FTP server to send a file to each interesting port of a

target host in turn. The error message will describe whether the

port is open or not. This is a good way to bypass firewalls because

organizational FTP servers are often placed where they have more

access to other internal hosts than any old Internet host would.

Nmap supports FTP bounce scan with the -b option. It takes an

argument of the form username:password@server:port. Server is the

name or IP address of a vulnerable FTP server. As with a normal

URL, you may omit username:password, in which case anonymous login

credentials (user: anonymous password:-wwwuser@) are used. The port

number (and preceding colon) may be omitted as well, in which case

the default FTP port (21) on server is used.

This vulnerability was widespread in 1997 when Nmap was released,

but has largely been fixed. Vulnerable servers are still around, so

it is worth trying when all else fails. If bypassing a firewall is

your goal, scan the target network for open port 21 (or even for

any FTP services if you scan all ports with version detection),

then try a bounce scan using each. Nmap will tell you whether the

host is vulnerable or not. If you are just trying to cover your

tracks, you don´t need to (and, in fact, shouldn´t) limit yourself

to hosts on the target network. Before you go scanning random

Internet addresses for vulnerable FTP servers, consider that

sysadmins may not appreciate you abusing their servers in this way.

PORT SPECIFICATION AND SCAN ORDER

In addition to all of the scan methods discussed previously, Nmap

offers options for specifying which ports are scanned and whether the

scan order is randomized or sequential. By default, Nmap scans the most

common 1,000 ports for each protocol.

-p port ranges (Only scan specified ports) .

This option specifies which ports you want to scan and overrides

the default. Individual port numbers are OK, as are ranges

separated by a hyphen (e.g. 1-1023). The beginning and/or end

values of a range may be omitted, causing Nmap to use 1 and 65535,

respectively. So you can specify -p- to scan ports from 1 through

65535. Scanning port zero. is allowed if you specify it

explicitly. For IP protocol scanning (-sO), this option specifies

the protocol numbers you wish to scan for (0–255).

When scanning both TCP and UDP ports, you can specify a particular

protocol by preceding the port numbers by T: or U:. The qualifier

lasts until you specify another qualifier. For example, the

argument -p U:53,111,137,T:21-25,80,139,8080 would scan UDP ports

53, 111,and 137, as well as the listed TCP ports. Note that to scan

both UDP and TCP, you have to specify -sU and at least one TCP scan

type (such as -sS, -sF, or -sT). If no protocol qualifier is given,

the port numbers are added to all protocol lists. Ports can also

be specified by name according to what the port is referred to in

the nmap-services. You can even use the wildcards * and ? with the

names. For example, to scan FTP and all ports whose names begin

with “http”, use -p ftp,http*. Be careful about shell expansions

and quote the argument to -p if unsure.

Ranges of ports can be surrounded by square brackets to indicate

ports inside that range that appear in nmap-services. For example,

the following will scan all ports in nmap-services equal to or

below 1024: -p [-1024]. Be careful with shell expansions and quote

the argument to -p if unsure.

-F (Fast (limited port) scan) .

Specifies that you wish to scan fewer ports than the default.

Normally Nmap scans the most common 1,000 ports for each scanned

protocol. With -F, this is reduced to 100.

Nmap needs an nmap-services file with frequency information in

order to know which ports are the most common. If port frequency

information isn´t available, perhaps because of the use of a custom

nmap-services file, -F means to scan only ports that are named in

the services file (normally Nmap scans all named ports plus ports

1–1024).

-r (Don´t randomize ports) .

By default, Nmap randomizes the scanned port order (except that

certain commonly accessible ports are moved near the beginning for

efficiency reasons). This randomization is normally desirable, but

you can specify -r for sequential (sorted from lowest to highest)

port scanning instead.

--port-ratio

Scans all ports in nmap-services file with a ratio greater than the

number specified as the argument.

--top-ports

Scans the N highest-ratio ports found in nmap-services file.

SERVICE AND VERSION DETECTION

Point Nmap at a remote machine and it might tell you that ports 25/tcp,

80/tcp, and 53/udp are open. Using its nmap-services. database of

about 2,200 well-known services,. Nmap would report that those ports

probably correspond to a mail server (SMTP), web server (HTTP), and

name server (DNS) respectively. This lookup is usually accurate—the

vast majority of daemons listening on TCP port 25 are, in fact, mail

servers. However, you should not bet your security on this! People can

and do run services on strange ports..

Even if Nmap is right, and the hypothetical server above is running

SMTP, HTTP, and DNS servers, that is not a lot of information. When

doing vulnerability assessments (or even simple network inventories) of

your companies or clients, you really want to know which mail and DNS

servers and versions are running. Having an accurate version number

helps dramatically in determining which exploits a server is vulnerable

to. Version detection helps you obtain this information.

After TCP and/or UDP ports are discovered using one of the other scan

methods, version detection interrogates those ports to determine more

about what is actually running. The nmap-service-probes. database

contains probes for querying various services and match expressions to

recognize and parse responses. Nmap tries to determine the service

protocol (e.g. FTP, SSH, Telnet, HTTP), the application name (e.g. ISC

BIND, Apache httpd, Solaris telnetd), the version number, hostname,

device type (e.g. printer, router), the OS family (e.g. Windows, Linux)

and sometimes miscellaneous details like whether an X server is open to

connections, the SSH protocol version, or the KaZaA user name). Of

course, most services don´t provide all of this information. If Nmap

was compiled with OpenSSL support, it will connect to SSL servers to

deduce the service listening behind that encryption layer.. When RPC

services are discovered, the Nmap RPC grinder. (-sR). is

automatically used to determine the RPC program and version numbers.

Some UDP ports are left in the open|filtered state after a UDP port

scan is unable to determine whether the port is open or filtered.

Version detection will try to elicit a response from these ports (just

as it does with open ports), and change the state to open if it

succeeds. open|filtered TCP ports are treated the same way. Note that

the Nmap -A option enables version detection among other things. A

paper documenting the workings, usage, and customization of version

detection is available at http://nmap.org/book/vscan.html.

When Nmap receives responses from a service but cannot match them to

its database, it prints out a special fingerprint and a URL for you to

submit if to if you know for sure what is running on the port. Please

take a couple minutes to make the submission so that your find can

benefit everyone. Thanks to these submissions, Nmap has about 3,000

pattern matches for more than 350 protocols such as SMTP, FTP, HTTP,

etc..

Version detection is enabled and controlled with the following options:

-sV (Version detection) .

Enables version detection, as discussed above. Alternatively, you

can use -A, which enables version detection among other things.

--allports (Don´t exclude any ports from version detection) .

By default, Nmap version detection skips TCP port 9100 because some

printers simply print anything sent to that port, leading to dozens

of pages of HTTP GET requests, binary SSL session requests, etc.

This behavior can be changed by modifying or removing the Exclude

directive in nmap-service-probes, or you can specify --allports to

scan all ports regardless of any Exclude directive.

--version-intensity intensity (Set version scan intensity) .

When performing a version scan (-sV), Nmap sends a series of

probes, each of which is assigned a rarity value between one and

nine. The lower-numbered probes are effective against a wide

variety of common services, while the higher numbered ones are

rarely useful. The intensity level specifies which probes should be

applied. The higher the number, the more likely it is the service

will be correctly identified. However, high intensity scans take

longer. The intensity must be between 0 and 9. The default is 7.

When a probe is registered to the target port via the

nmap-service-probes ports directive, that probe is tried regardless

of intensity level. This ensures that the DNS probes will always be

attempted against any open port 53, the SSL probe will be done

against 443, etc.

--version-light (Enable light mode) .

This is a convenience alias for --version-intensity 2. This light

mode makes version scanning much faster, but it is slightly less

likely to identify services.

--version-all (Try every single probe) .

An alias for --version-intensity 9, ensuring that every single

probe is attempted against each port.

--version-trace (Trace version scan activity) .

This causes Nmap to print out extensive debugging info about what

version scanning is doing. It is a subset of what you get with

--packet-trace.

-sR (RPC scan) .

This method works in conjunction with the various port scan methods

of Nmap. It takes all the TCP/UDP ports found open and floods them

with SunRPC program NULL commands in an attempt to determine

whether they are RPC ports, and if so, what program and version

number they serve up. Thus you can effectively obtain the same info

as rpcinfo -p even if the target´s portmapper is behind a firewall

(or protected by TCP wrappers). Decoys do not currently work with

RPC scan.. This is automatically enabled as part of version scan

(-sV) if you request that. As version detection includes this and

is much more comprehensive, -sR is rarely needed.

OS DETECTION

One of Nmap´s best-known features is remote OS detection using TCP/IP

stack fingerprinting. Nmap sends a series of TCP and UDP packets to the

remote host and examines practically every bit in the responses. After

performing dozens of tests such as TCP ISN sampling, TCP options

support and ordering, IP ID sampling, and the initial window size

check, Nmap compares the results to its nmap-os-db. database of more

than a thousand known OS fingerprints and prints out the OS details if

there is a match. Each fingerprint includes a freeform textual

description of the OS, and a classification which provides the vendor

name (e.g. Sun), underlying OS (e.g. Solaris), OS generation (e.g. 10),

and device type (general purpose, router, switch, game console, etc).

If Nmap is unable to guess the OS of a machine, and conditions are good

(e.g. at least one open port and one closed port were found), Nmap will

provide a URL you can use to submit the fingerprint if you know (for

sure) the OS running on the machine. By doing this you contribute to

the pool of operating systems known to Nmap and thus it will be more

accurate for everyone.

OS detection enables some other tests which make use of information

that is gathered during the process anyway. One of these is TCP

Sequence Predictability Classification. This measures approximately how

hard it is to establish a forged TCP connection against the remote

host. It is useful for exploiting source-IP based trust relationships

(rlogin, firewall filters, etc) or for hiding the source of an attack.

This sort of spoofing is rarely performed any more, but many machines

are still vulnerable to it. The actual difficulty number is based on

statistical sampling and may fluctuate. It is generally better to use

the English classification such as “worthy challenge” or “trivial

joke”. This is only reported in normal output in verbose (-v) mode.

When verbose mode is enabled along with -O, IP ID sequence generation

is also reported. Most machines are in the “incremental” class, which

means that they increment the ID field in the IP header for each packet

they send. This makes them vulnerable to several advanced information

gathering and spoofing attacks.

Another bit of extra information enabled by OS detection is a guess at

a target´s uptime. This uses the TCP timestamp option (RFC 1323[10]) to

guess when a machine was last rebooted. The guess can be inaccurate due

to the timestamp counter not being initialized to zero or the counter

overflowing and wrapping around, so it is printed only in verbose mode.

A paper documenting the workings, usage, and customization of OS

detection is available at http://nmap.org/book/osdetect.html.

OS detection is enabled and controlled with the following options:

-O (Enable OS detection) .

Enables OS detection, as discussed above. Alternatively, you can

use -A to enable OS detection along with other things.

--osscan-limit (Limit OS detection to promising targets) .

OS detection is far more effective if at least one open and one

closed TCP port are found. Set this option and Nmap will not even

try OS detection against hosts that do not meet this criteria. This

can save substantial time, particularly on -PN scans against many

hosts. It only matters when OS detection is requested with -O or

-A.

--osscan-guess; --fuzzy (Guess OS detection results) .

When Nmap is unable to detect a perfect OS match, it sometimes

offers up near-matches as possibilities. The match has to be very

close for Nmap to do this by default. Either of these (equivalent)

options make Nmap guess more aggressively. Nmap will still tell you

when an imperfect match is printed and display its confidence level

(percentage) for each guess.

--max-os-tries (Set the maximum number of OS detection tries against a

target) .

When Nmap performs OS detection against a target and fails to find

a perfect match, it usually repeats the attempt. By default, Nmap

tries five times if conditions are favorable for OS fingerprint

submission, and twice when conditions aren´t so good. Specifying a

lower --max-os-tries value (such as 1) speeds Nmap up, though you

miss out on retries which could potentially identify the OS.

Alternatively, a high value may be set to allow even more retries

when conditions are favorable. This is rarely done, except to

generate better fingerprints for submission and integration into

the Nmap OS database.

NMAP SCRIPTING ENGINE (NSE)

The Nmap Scripting Engine (NSE) is one of Nmap´s most powerful and

flexible features. It allows users to write (and share) simple scripts

(using the Lua programming language[11],

Tasks we had in mind when creating the system include network

discovery, more sophisticated version detection, vulnerability

detection. NSE can even be used for vulnerability exploitation.

To reflect those different uses and to simplify the choice of which

scripts to run, each script contains a field associating it with one or

more categories. Currently defined categories are safe, intrusive,

malware, version, discovery, vuln, auth, and default. These are all

described at http://nmap.org/book/nse-usage.html#nse-categories.

Scripts are not run in a sandbox and thus could accidentally or

maliciously damage your system or invade your privacy. Never run

scripts from third parties unless you trust the authors or have

carefully audited the scripts yourself.

The Nmap Scripting Engine is described in detail at

http://nmap.org/book/nse.html

and is controlled by the following options:

-sC .

Performs a script scan using the default set of scripts. It is

equivalent to --script=default. Some of the scripts in this

category are considered intrusive and should not be run against a

target network without permission.

--script filename|category|directory|expression|all[,...] .

Runs a script scan using the comma-separated list of filenames,

script categories, and directories. Each element in the list may

also be a Boolean expression describing a more complex set of

scripts. Each element is interpreted first as an expression, then

as a category, and finally as a file or directory name. The special

argument all makes every script in Nmap´s script database eligible

to run. The all argument should be used with caution as NSE may

contain dangerous scripts including exploits, brute force

authentication crackers, and denial of service attacks.

File and directory names may be relative or absolute. Absolute

names are used directly. Relative paths are looked for in the

following places until found:

--datadir

$NMAPDIR

~/.nmap (not searched on Windows)

NMAPDATADIR

the current directory

A scripts subdirectory is also tried in each of these.

When a directory name is given, Nmap loads every file in the

directory whose name ends with .nse. All other files are ignored

and directories are not searched recursively. When a filename is

given, it does not have to have the .nse extension; it will be

added automatically if necessary. Nmap scripts are stored in a

scripts subdirectory of the Nmap data directory by default (see

http://nmap.org/book/data-files.html).

For efficiency, scripts are indexed in a database stored in

scripts/script.db,. which lists the category or categories in

which each script belongs. When referring to scripts from

script.db by name, you can use a shell-style ‘*’ wildcard.

nmap --script "http-*"

Loads all scripts whose name starts with http-, such as

http-auth.nse and http-open-proxy.nse. The argument to --script

had to be in quotes to protect the wildcard from the shell.

More complicated script selection can be done using the and, or,

and not operators to build Boolean expressions. The operators have

the same precedence[12] as in Lua: not is the highest, followed by

and and then or. You can alter precedence by using parentheses.

Because expressions contain space characters it is necessary to

quote them.

nmap --script "not intrusive"

Loads every script except for those in the intrusive category.

nmap --script "default or safe"

This is functionally equivalent to nmap --script

"default,safe". It loads all scripts that are in the default

category or the safe category or both.

nmap --script "default and safe"

Loads those scripts that are in both the default and safe

categories.

nmap --script "(default or safe or intrusive) and not http-*"

Loads scripts in the default, safe, or intrusive categories,

except for those whose names start with http-.

--script-args name1=value1,name2={name3=value3},name4={value4,value5} .

Lets you provide arguments to NSE scripts. Arguments are a

comma-separated list of name=value pairs. Names and values may be

strings not containing whitespace or the characters ‘{’, ‘}’, ‘=’,

or ‘,’. To include one of these characters in a string, enclose the

string in single or double quotes. Within a quoted string, ‘/’

escapes a quote. A backslash is only used to escape quotation marks

in this special case; in all other cases a backslash is interpreted

literally. Values may also be tables enclosed in {}, just as in

Lua. A table may contain simple string values or more name-value

pairs, including nested tables. An example of script arguments:

--script-args

auth={user=foo,pass=´,{}=bar´},userdb=C:/Path/To/File. The online

NSE Documentation Portal at http://nmap.org/nsedoc/ lists the

arguments that each script accepts.

--script-trace .

This option does what --packet-trace does, just one ISO layer

higher. If this option is specified all incoming and outgoing

communication performed by a script is printed. The displayed

information includes the communication protocol, the source, the

target and the transmitted data. If more than 5% of all transmitted

data is not printable, then the trace output is in a hex dump

format. Specifying --packet-trace enables script tracing too.

--script-updatedb .

This option updates the script database found in scripts/script.db

which is used by Nmap to determine the available default scripts

and categories. It is only necessary to update the database if you

have added or removed NSE scripts from the default scripts

directory or if you have changed the categories of any script. This

option is generally used by itself: nmap --script-updatedb.

TIMING AND PERFORMANCE

One of my highest Nmap development priorities has always been

performance. A default scan (nmap hostname) of a host on my local

network takes a fifth of a second. That is barely enough time to blink,

but adds up when you are scanning hundreds or thousands of hosts.

Moreover, certain scan options such as UDP scanning and version

detection can increase scan times substantially. So can certain

firewall configurations, particularly response rate limiting. While

Nmap utilizes parallelism and many advanced algorithms to accelerate

these scans, the user has ultimate control over how Nmap runs. Expert

users carefully craft Nmap commands to obtain only the information they

care about while meeting their time constraints.

Techniques for improving scan times include omitting non-critical

tests, and upgrading to the latest version of Nmap (performance

enhancements are made frequently). Optimizing timing parameters can

also make a substantial difference. Those options are listed below.

Some options accept a time parameter. This is specified in milliseconds

by default, though you can append ‘s’, ‘m’, or ‘h’ to the value to

specify seconds, minutes, or hours. So the --host-timeout arguments

900000, 900s, and 15m all do the same thing.

--min-hostgroup numhosts; --max-hostgroup numhosts (Adjust parallel

scan group sizes) .

Nmap has the ability to port scan or version scan multiple hosts in

parallel. Nmap does this by dividing the target IP space into

groups and then scanning one group at a time. In general, larger

groups are more efficient. The downside is that host results can´t

be provided until the whole group is finished. So if Nmap started

out with a group size of 50, the user would not receive any reports

(except for the updates offered in verbose mode) until the first 50

hosts are completed.

By default, Nmap takes a compromise approach to this conflict. It

starts out with a group size as low as five so the first results

come quickly and then increases the groupsize to as high as 1024.

The exact default numbers depend on the options given. For

efficiency reasons, Nmap uses larger group sizes for UDP or

few-port TCP scans.

When a maximum group size is specified with --max-hostgroup, Nmap

will never exceed that size. Specify a minimum size with

--min-hostgroup and Nmap will try to keep group sizes above that

level. Nmap may have to use smaller groups than you specify if

there are not enough target hosts left on a given interface to

fulfill the specified minimum. Both may be set to keep the group

size within a specific range, though this is rarely desired.

These options do not have an effect during the host discovery phase

of a scan. This includes plain ping scans (-sP). Host discovery

always works in large groups of hosts to improve speed and

accuracy.

The primary use of these options is to specify a large minimum

group size so that the full scan runs more quickly. A common choice

is 256 to scan a network in Class C sized chunks. For a scan with

many ports, exceeding that number is unlikely to help much. For

scans of just a few port numbers, host group sizes of 2048 or more

may be helpful.

--min-parallelism numprobes; --max-parallelism numprobes (Adjust probe

parallelization) .

These options control the total number of probes that may be

outstanding for a host group. They are used for port scanning and

host discovery. By default, Nmap calculates an ever-changing ideal

parallelism based on network performance. If packets are being

dropped, Nmap slows down and allows fewer outstanding probes. The

ideal probe number slowly rises as the network proves itself

worthy. These options place minimum or maximum bounds on that

variable. By default, the ideal parallelism can drop to one if the

network proves unreliable and rise to several hundred in perfect

conditions.

The most common usage is to set --min-parallelism to a number

higher than one to speed up scans of poorly performing hosts or

networks. This is a risky option to play with, as setting it too

high may affect accuracy. Setting this also reduces Nmap´s ability

to control parallelism dynamically based on network conditions. A

value of ten might be reasonable, though I only adjust this value

as a last resort.

The --max-parallelism option is sometimes set to one to prevent

Nmap from sending more than one probe at a time to hosts. The

--scan-delay option, discussed later, is another way to do this.

--min-rtt-timeout time, --max-rtt-timeout time, --initial-rtt-timeout

time (Adjust probe timeouts) .

Nmap maintains a running timeout value for determining how long it

will wait for a probe response before giving up or retransmitting

the probe. This is calculated based on the response times of

previous probes.

If the network latency shows itself to be significant and variable,

this timeout can grow to several seconds. It also starts at a

conservative (high) level and may stay that way for a while when

Nmap scans unresponsive hosts.

Specifying a lower --max-rtt-timeout and --initial-rtt-timeout than

the defaults can cut scan times significantly. This is particularly

true for pingless (-PN) scans, and those against heavily filtered

networks. Don´t get too aggressive though. The scan can end up

taking longer if you specify such a low value that many probes are

timing out and retransmitting while the response is in transit.

If all the hosts are on a local network, 100 milliseconds is a

reasonable aggressive --max-rtt-timeout value. If routing is

involved, ping a host on the network first with the ICMP ping

utility, or with a custom packet crafter such as hping2. that is

more likely to get through a firewall. Look at the maximum round

trip time out of ten packets or so. You might want to double that

for the --initial-rtt-timeout and triple or quadruple it for the

--max-rtt-timeout. I generally do not set the maximum RTT below

100 ms, no matter what the ping times are. Nor do I exceed 1000 ms.

--min-rtt-timeout is a rarely used option that could be useful when

a network is so unreliable that even Nmap´s default is too

aggressive. Since Nmap only reduces the timeout down to the minimum

when the network seems to be reliable, this need is unusual and

should be reported as a bug to the nmap-dev mailing list..

--max-retries numtries (Specify the maximum number of port scan probe

retransmissions) .

When Nmap receives no response to a port scan probe, it could mean

the port is filtered. Or maybe the probe or response was simply

lost on the network. It is also possible that the target host has

rate limiting enabled that temporarily blocked the response. So

Nmap tries again by retransmitting the initial probe. If Nmap

detects poor network reliability, it may try many more times before

giving up on a port. While this benefits accuracy, it also lengthen

scan times. When performance is critical, scans may be sped up by

limiting the number of retransmissions allowed. You can even

specify --max-retries 0 to prevent any retransmissions, though that

is only recommended for situations such as informal surveys where

occasional missed ports and hosts are acceptable.

The default (with no -T template) is to allow ten retransmissions.

If a network seems reliable and the target hosts aren´t rate

limiting, Nmap usually only does one retransmission. So most target

scans aren´t even affected by dropping --max-retries to a low value

such as three. Such values can substantially speed scans of slow

(rate limited) hosts. You usually lose some information when Nmap

gives up on ports early, though that may be preferable to letting

the --host-timeout expire and losing all information about the

target.

--host-timeout time (Give up on slow target hosts) .

Some hosts simply take a long time to scan. This may be due to

poorly performing or unreliable networking hardware or software,

packet rate limiting, or a restrictive firewall. The slowest few

percent of the scanned hosts can eat up a majority of the scan

time. Sometimes it is best to cut your losses and skip those hosts

initially. Specify --host-timeout with the maximum amount of time

you are willing to wait. For example, specify 30m to ensure that

Nmap doesn´t waste more than half an hour on a single host. Note

that Nmap may be scanning other hosts at the same time during that

half an hour, so it isn´t a complete loss. A host that times out is

skipped. No port table, OS detection, or version detection results

are printed for that host.

--scan-delay time; --max-scan-delay time (Adjust delay between probes)

.

This option causes Nmap to wait at least the given amount of time

between each probe it sends to a given host. This is particularly

useful in the case of rate limiting.. Solaris machines (among many

others) will usually respond to UDP scan probe packets with only

one ICMP message per second. Any more than that sent by Nmap will

be wasteful. A --scan-delay of 1s will keep Nmap at that slow rate.

Nmap tries to detect rate limiting and adjust the scan delay

accordingly, but it doesn´t hurt to specify it explicitly if you

already know what rate works best.

When Nmap adjusts the scan delay upward to cope with rate limiting,

the scan slows down dramatically. The --max-scan-delay option

specifies the largest delay that Nmap will allow. A low

--max-scan-delay can speed up Nmap, but it is risky. Setting this

value too low can lead to wasteful packet retransmissions and

possible missed ports when the target implements strict rate

limiting.

Another use of --scan-delay is to evade threshold based intrusion

detection and prevention systems (IDS/IPS)..

--min-rate number; --max-rate number (Directly control the scanning

rate) .

Nmap´s dynamic timing does a good job of finding an appropriate

speed at which to scan. Sometimes, however, you may happen to know

an appropriate scanning rate for a network, or you may have to

guarantee that a scan will be finished by a certain time. Or

perhaps you must keep Nmap from scanning too quickly. The

--min-rate and --max-rate options are designed for these

situations.

When the --min-rate option is given Nmap will do its best to send

packets as fast as or faster than the given rate. The argument is a

positive real number representing a packet rate in packets per

second. For example, specifying --min-rate 300 means that Nmap will

try to keep the sending rate at or above 300 packets per second.

Specifying a minimum rate does not keep Nmap from going faster if

conditions warrant.

Likewise, --max-rate limits a scan´s sending rate to a given

maximum. Use --max-rate 100, for example, to limit sending to 100

packets per second on a fast network. Use --max-rate 0.1 for a slow

scan of one packet every ten seconds. Use --min-rate and --max-rate

together to keep the rate inside a certain range.

These two options are global, affecting an entire scan, not

individual hosts. They only affect port scans and host discovery

scans. Other features like OS detection implement their own timing.

There are two conditions when the actual scanning rate may fall

below the requested minimum. The first is if the minimum is faster

than the fastest rate at which Nmap can send, which is dependent on

hardware. In this case Nmap will simply send packets as fast as

possible, but be aware that such high rates are likely to cause a

loss of accuracy. The second case is when Nmap has nothing to send,

for example at the end of a scan when the last probes have been

sent and Nmap is waiting for them to time out or be responded to.

It´s normal to see the scanning rate drop at the end of a scan or

in between hostgroups. The sending rate may temporarily exceed the

maximum to make up for unpredictable delays, but on average the

rate will stay at or below the maximum.

Specifying a minimum rate should be done with care. Scanning faster

than a network can support may lead to a loss of accuracy. In some

cases, using a faster rate can make a scan take longer than it

would with a slower rate. This is because Nmap´s

adaptive retransmission algorithms will detect the network

congestion caused by an excessive scanning rate and increase the

number of retransmissions in order to improve accuracy. So even

though packets are sent at a higher rate, more packets are sent

overall. Cap the number of retransmissions with the --max-retries

option if you need to set an upper limit on total scan time.

--defeat-rst-ratelimit .

Many hosts have long used rate limiting. to reduce the number of

ICMP error messages (such as port-unreachable errors) they send.

Some systems now apply similar rate limits to the RST (reset)

packets they generate. This can slow Nmap down dramatically as it

adjusts its timing to reflect those rate limits. You can tell Nmap

to ignore those rate limits (for port scans such as SYN scan which

don´t treat non-responsive ports as open) by specifying

--defeat-rst-ratelimit.

Using this option can reduce accuracy, as some ports will appear

non-responsive because Nmap didn´t wait long enough for a

rate-limited RST response. With a SYN scan, the non-response

results in the port being labeled filtered rather than the closed

state we see when RST packets are received. This option is useful

when you only care about open ports, and distinguishing between

closed and filtered ports isn´t worth the extra time.

-T paranoid|sneaky|polite|normal|aggressive|insane (Set a timing

template) .

While the fine-grained timing controls discussed in the previous

section are powerful and effective, some people find them

confusing. Moreover, choosing the appropriate values can sometimes

take more time than the scan you are trying to optimize. So Nmap

offers a simpler approach, with six timing templates. You can

specify them with the -T option and their number (0–5) or their

name. The template names are paranoid (0), sneaky (1), polite (2),

normal (3), aggressive (4), and insane (5). The first two are for

IDS evasion. Polite mode slows down the scan to use less bandwidth

and target machine resources. Normal mode is the default and so -T3

does nothing. Aggressive mode speeds scans up by making the

assumption that you are on a reasonably fast and reliable network.

Finally insane mode. assumes that you are on an extraordinarily

fast network or are willing to sacrifice some accuracy for speed.

These templates allow the user to specify how aggressive they wish

to be, while leaving Nmap to pick the exact timing values. The

templates also make some minor speed adjustments for which

fine-grained control options do not currently exist. For example,

-T4. prohibits the dynamic scan delay from exceeding 10 ms for TCP

ports and -T5 caps that value at 5 ms. Templates can be used in

combination with fine-grained controls, and the fine-grained

controls will you specify will take precedence over the timing

template default for that parameter. I recommend using -T4 when

scanning reasonably modern and reliable networks. Keep that option

even when you add fine-grained controls so that you benefit from

those extra minor optimizations that it enables.

If you are on a decent broadband or ethernet connection, I would

recommend always using -T4. Some people love -T5 though it is too

aggressive for my taste. People sometimes specify -T2 because they

think it is less likely to crash hosts or because they consider

themselves to be polite in general. They often don´t realize just

how slow -T polite. really is. Their scan may take ten times

longer than a default scan. Machine crashes and bandwidth problems

are rare with the default timing options (-T3) and so I normally

recommend that for cautious scanners. Omitting version detection is

far more effective than playing with timing values at reducing

these problems.

While -T0. and -T1. may be useful for avoiding IDS alerts, they

will take an extraordinarily long time to scan thousands of

machines or ports. For such a long scan, you may prefer to set the

exact timing values you need rather than rely on the canned -T0 and

-T1 values.

The main effects of T0 are serializing the scan so only one port is

scanned at a time, and waiting five minutes between sending each

probe. T1 and T2 are similar but they only wait 15 seconds and 0.4

seconds, respectively, between probes. T3 is Nmap´s default

behavior, which includes parallelization.. -T4 does the equivalent

of --max-rtt-timeout 1250 --initial-rtt-timeout 500 --max-retries 6

and sets the maximum TCP scan delay to 10 milliseconds. T5 does

the equivalent of --max-rtt-timeout 300 --min-rtt-timeout 50

--initial-rtt-timeout 250 --max-retries 2 --host-timeout 15m as

well as setting the maximum TCP scan delay to 5 ms.

FIREWALL/IDS EVASION AND SPOOFING

Many Internet pioneers envisioned a global open network with a

universal IP address space allowing virtual connections between any two

nodes. This allows hosts to act as true peers, serving and retrieving

information from each other. People could access all of their home

systems from work, changing the climate control settings or unlocking

the doors for early guests. This vision of universal connectivity has

been stifled by address space shortages and security concerns. In the

early 1990s, organizations began deploying firewalls for the express

purpose of reducing connectivity. Huge networks were cordoned off from

the unfiltered Internet by application proxies, network address

translation, and packet filters. The unrestricted flow of information

gave way to tight regulation of approved communication channels and the

content that passes over them.

Network obstructions such as firewalls can make mapping a network

exceedingly difficult. It will not get any easier, as stifling casual

reconnaissance is often a key goal of implementing the devices.

Nevertheless, Nmap offers many features to help understand these

complex networks, and to verify that filters are working as intended.

It even supports mechanisms for bypassing poorly implemented defenses.

One of the best methods of understanding your network security posture

is to try to defeat it. Place yourself in the mind-set of an attacker,

and deploy techniques from this section against your networks. Launch

an FTP bounce scan, idle scan, fragmentation attack, or try to tunnel

through one of your own proxies.

In addition to restricting network activity, companies are increasingly

monitoring traffic with intrusion detection systems (IDS). All of the

major IDSs ship with rules designed to detect Nmap scans because scans

are sometimes a precursor to attacks. Many of these products have

recently morphed into intrusion prevention systems (IPS). that

actively block traffic deemed malicious. Unfortunately for network

administrators and IDS vendors, reliably detecting bad intentions by

analyzing packet data is a tough problem. Attackers with patience,

skill, and the help of certain Nmap options can usually pass by IDSs

undetected. Meanwhile, administrators must cope with large numbers of

false positive results where innocent activity is misdiagnosed and

alerted on or blocked.

Occasionally people suggest that Nmap should not offer features for

evading firewall rules or sneaking past IDSs. They argue that these

features are just as likely to be misused by attackers as used by

administrators to enhance security. The problem with this logic is that

these methods would still be used by attackers, who would just find

other tools or patch the functionality into Nmap. Meanwhile,

administrators would find it that much harder to do their jobs.

Deploying only modern, patched FTP servers is a far more powerful

defense than trying to prevent the distribution of tools implementing

the FTP bounce attack.

There is no magic bullet (or Nmap option) for detecting and subverting

firewalls and IDS systems. It takes skill and experience. A tutorial is

beyond the scope of this reference guide, which only lists the relevant

options and describes what they do.

-f (fragment packets); --mtu (using the specified MTU) .

The -f option causes the requested scan (including ping scans) to

use tiny fragmented IP packets. The idea is to split up the TCP

header over several packets to make it harder for packet filters,

intrusion detection systems, and other annoyances to detect what

you are doing. Be careful with this! Some programs have trouble

handling these tiny packets. The old-school sniffer named Sniffit

segmentation faulted immediately upon receiving the first fragment.

Specify this option once, and Nmap splits the packets into eight

bytes or less after the IP header. So a 20-byte TCP header would be

split into three packets. Two with eight bytes of the TCP header,

and one with the final four. Of course each fragment also has an IP

header. Specify -f again to use 16 bytes per fragment (reducing the

number of fragments).. Or you can specify your own offset size

with the --mtu option. Don´t also specify -f if you use --mtu. The

offset must be a multiple of eight. While fragmented packets won´t

get by packet filters and firewalls that queue all IP fragments,

such as the CONFIG_IP_ALWAYS_DEFRAG option in the Linux kernel,

some networks can´t afford the performance hit this causes and thus

leave it disabled. Others can´t enable this because fragments may

take different routes into their networks. Some source systems

defragment outgoing packets in the kernel. Linux with the iptables.

connection tracking module is one such example. Do a scan while a

sniffer such as Wireshark. is running to ensure that sent packets

are fragmented. If your host OS is causing problems, try the

--send-eth. option to bypass the IP layer and send raw ethernet

frames.

Fragmentation is only supported for Nmap´s raw packet features,

which includes TCP and UDP port scans (except connect scan and FTP

bounce scan) and OS detection. Features such as version detection

and the Nmap Scripting Engine generally don´t support fragmentation

because they rely on your host´s TCP stack to communicate with

target services.

-D decoy1[,decoy2][,ME][,...] (Cloak a scan with decoys) .

Causes a decoy scan to be performed, which makes it appear to the

remote host that the host(s) you specify as decoys are scanning the

target network too. Thus their IDS might report 5–10 port scans

from unique IP addresses, but they won´t know which IP was scanning

them and which were innocent decoys. While this can be defeated

through router path tracing, response-dropping, and other active

mechanisms, it is generally an effective technique for hiding your

IP address.

Separate each decoy host with commas, and you can optionally use

ME. as one of the decoys to represent the position for your real

IP address. If you put ME in the sixth position or later, some

common port scan detectors (such as Solar Designer´s. excellent

Scanlogd). are unlikely to show your IP address at all. If you

don´t use ME, Nmap will put you in a random position. You can also

use RND. to generate a random, non-reserved IP address, or

RND:number to generate number addresses.

Note that the hosts you use as decoys should be up or you might

accidentally SYN flood your targets. Also it will be pretty easy to

determine which host is scanning if only one is actually up on the

network. You might want to use IP addresses instead of names (so

the decoy networks don´t see you in their nameserver logs).

Decoys are used both in the initial ping scan (using ICMP, SYN,

ACK, or whatever) and during the actual port scanning phase. Decoys

are also used during remote OS detection (-O). Decoys do not work

with version detection or TCP connect scan. When a scan delay is in

effect, the delay is enforced between each batch of spoofed probes,

not between each individual probe. Because decoys are sent as a

batch all at once, they may temporarily violate congestion control

limits.

It is worth noting that using too many decoys may slow your scan

and potentially even make it less accurate. Also, some ISPs will

filter out your spoofed packets, but many do not restrict spoofed

IP packets at all.

-S IP_Address (Spoof source address) .

In some circumstances, Nmap may not be able to determine your

source address (Nmap will tell you if this is the case). In this

situation, use -S with the IP address of the interface you wish to

send packets through.

Another possible use of this flag is to spoof the scan to make the

targets think that someone else is scanning them. Imagine a company

being repeatedly port scanned by a competitor! The -e option and

-PN are generally required for this sort of usage. Note that you

usually won´t receive reply packets back (they will be addressed to

the IP you are spoofing), so Nmap won´t produce useful reports.

-e interface (Use specified interface) .

Tells Nmap what interface to send and receive packets on. Nmap

should be able to detect this automatically, but it will tell you

if it cannot.

--source-port portnumber; -g portnumber (Spoof source port number) .

One surprisingly common misconfiguration is to trust traffic based

only on the source port number. It is easy to understand how this

comes about. An administrator will set up a shiny new firewall,

only to be flooded with complains from ungrateful users whose

applications stopped working. In particular, DNS may be broken

because the UDP DNS replies from external servers can no longer

enter the network. FTP is another common example. In active FTP

transfers, the remote server tries to establish a connection back

to the client to transfer the requested file.

Secure solutions to these problems exist, often in the form of

application-level proxies or protocol-parsing firewall modules.

Unfortunately there are also easier, insecure solutions. Noting

that DNS replies come from port 53 and active FTP from port 20,

many administrators have fallen into the trap of simply allowing

incoming traffic from those ports. They often assume that no

attacker would notice and exploit such firewall holes. In other

cases, administrators consider this a short-term stop-gap measure

until they can implement a more secure solution. Then they forget

the security upgrade.

Overworked network administrators are not the only ones to fall

into this trap. Numerous products have shipped with these insecure

rules. Even Microsoft has been guilty. The IPsec filters that

shipped with Windows 2000 and Windows XP contain an implicit rule

that allows all TCP or UDP traffic from port 88 (Kerberos). In

another well-known case, versions of the Zone Alarm personal

firewall up to 2.1.25 allowed any incoming UDP packets with the

source port 53 (DNS) or 67 (DHCP).

Nmap offers the -g and --source-port options (they are equivalent)

to exploit these weaknesses. Simply provide a port number and Nmap

will send packets from that port where possible. Nmap must use

different port numbers for certain OS detection tests to work

properly, and DNS requests ignore the --source-port flag because

Nmap relies on system libraries to handle those. Most TCP scans,

including SYN scan, support the option completely, as does UDP

scan.

--data-length number (Append random data to sent packets) .

Normally Nmap sends minimalist packets containing only a header. So

its TCP packets are generally 40 bytes and ICMP echo requests are

just 28. Some UDP ports. and IP protocols. get a custom payload

by default. This option tells Nmap to append the given number of

random bytes to most of the packets it sends, and not to use any

protocol-specific payloads. (Use --data-length 0 for no random or

protocol-specific payloads.. OS detection (-O) packets are not

affected. because accuracy there requires probe consistency, but

most pinging and portscan packets support this. It slows things

down a little, but can make a scan slightly less conspicuous.

--ip-options S|R [route]|L [route]|T|U ... ; --ip-options hex string

(Send packets with specified ip options) .

The IP protocol[13] offers several options which may be placed in

packet headers. Unlike the ubiquitous TCP options, IP options are

rarely seen due to practicality and security concerns. In fact,

many Internet routers block the most dangerous options such as

source routing. Yet options can still be useful in some cases for

determining and manipulating the network route to target machines.

For example, you may be able to use the record route option to

determine a path to a target even when more traditional

traceroute-style approaches fail. Or if your packets are being

dropped by a certain firewall, you may be able to specify a

different route with the strict or loose source routing options.

The most powerful way to specify IP options is to simply pass in

values as the argument to --ip-options. Precede each hex number

with /x then the two digits. You may repeat certain characters by

following them with an asterisk and then the number of times you

wish them to repeat. For example, /x01/x07/x04/x00*36/x01 is a hex

string containing 36 NUL bytes.

Nmap also offers a shortcut mechanism for specifying options.

Simply pass the letter R, T, or U to request record-route,.

record-timestamp,. or both options together, respectively. Loose

or strict source routing. may be specified with an L or S followed

by a space and then a space-separated list of IP addresses.

If you wish to see the options in packets sent and received,

specify --packet-trace. For more information and examples of using

IP options with Nmap, see

http://seclists.org/nmap-dev/2006/q3/0052.html.

--ttl value (Set IP time-to-live field) .

Sets the IPv4 time-to-live field in sent packets to the given

value.

--randomize-hosts (Randomize target host order) .

Tells Nmap to shuffle each group of up to 16384 hosts before it

scans them. This can make the scans less obvious to various network

monitoring systems, especially when you combine it with slow timing

options. If you want to randomize over larger group sizes, increase

PING_GROUP_SZ. in nmap.h. and recompile. An alternative solution

is to generate the target IP list with a list scan (-sL -n -oN

filename), randomize it with a Perl script, then provide the whole

list to Nmap with -iL..

--spoof-mac MAC address, prefix, or vendor name (Spoof MAC address) .

Asks Nmap to use the given MAC address for all of the raw ethernet

frames it sends. This option implies --send-eth. to ensure that

Nmap actually sends ethernet-level packets. The MAC given can take

several formats. If it is simply the number 0, Nmap chooses a

completely random MAC address for the session. If the given string

is an even number of hex digits (with the pairs optionally

separated by a colon), Nmap will use those as the MAC. If fewer

than 12 hex digits are provided, Nmap fills in the remainder of the

six bytes with random values. If the argument isn´t a zero or hex

string, Nmap looks through nmap-mac-prefixes to find a vendor name

containing the given string (it is case insensitive). If a match is

found, Nmap uses the vendor´s OUI (three-byte prefix). and fills

out the remaining three bytes randomly. Valid --spoof-mac argument

examples are Apple, 0, 01:02:03:04:05:06, deadbeefcafe, 0020F2, and

Cisco. This option only affects raw packet scans such as SYN scan

or OS detection, not connection-oriented features such as version

detection or the Nmap Scripting Engine.

--badsum (Send packets with bogus TCP/UDP checksums) .

Asks Nmap to use an invalid TCP, UDP or SCTP checksum for packets

sent to target hosts. Since virtually all host IP stacks properly

drop these packets, any responses received are likely coming from a

firewall or IDS that didn´t bother to verify the checksum. For more

details on this technique, see http://nmap.org/p60-12.html

--adler32 (Use deprecated Adler32 instead of CRC32C for SCTP checksums)

.

Asks Nmap to use the deprecated Adler32 algorithm for calculating

the SCTP checksum. If --adler32 is not given, CRC-32C (Castagnoli)

is used. RFC 2960[14] originally defined Adler32 as checksum

algorithm for SCTP; RFC 4960[7] later redefined the SCTP checksums

to use CRC-32C. Current SCTP implementations should be using

CRC-32C, but in order to elicit responses from old, legacy SCTP

implementations, it may be preferrable to use Adler32.

OUTPUT

Any security tool is only as useful as the output it generates. Complex

tests and algorithms are of little value if they aren´t presented in an

organized and comprehensible fashion. Given the number of ways Nmap is

used by people and other software, no single format can please

everyone. So Nmap offers several formats, including the interactive

mode for humans to read directly and XML for easy parsing by software.

In addition to offering different output formats, Nmap provides options

for controlling the verbosity of output as well as debugging messages.

Output types may be sent to standard output or to named files, which

Nmap can append to or clobber. Output files may also be used to resume

aborted scans.

Nmap makes output available in five different formats. The default is

called interactive output,. and it is sent to standard output

(stdout).. There is also normal output,. which is similar to

interactive except that it displays less runtime information and

warnings since it is expected to be analyzed after the scan completes

rather than interactively.

XML output. is one of the most important output types, as it can be

converted to HTML, easily parsed by programs such as Nmap graphical

user interfaces, or imported into databases.

The two remaining output types are the simple grepable output. which

includes most information for a target host on a single line, and

sCRiPt KiDDi3 0utPUt. for users who consider themselves |<-r4d.

While interactive output is the default and has no associated

command-line options, the other four format options use the same

syntax. They take one argument, which is the filename that results

should be stored in. Multiple formats may be specified, but each format

may only be specified once. For example, you may wish to save normal

output for your own review while saving XML of the same scan for

programmatic analysis. You might do this with the options -oX

myscan.xml -oN myscan.nmap. While this chapter uses the simple names

like myscan.xml for brevity, more descriptive names are generally

recommended. The names chosen are a matter of personal preference,

though I use long ones that incorporate the scan date and a word or two

describing the scan, placed in a directory named after the company I´m

scanning.

While these options save results to files, Nmap still prints

interactive output to stdout as usual. For example, the command nmap

-oX myscan.xml target prints XML to myscan.xml and fills standard

output with the same interactive results it would have printed if -oX

wasn´t specified at all. You can change this by passing a hyphen

character as the argument to one of the format types. This causes Nmap

to deactivate interactive output, and instead print results in the

format you specified to the standard output stream. So the command nmap

-oX - target will send only XML output to stdout.. Serious errors may

still be printed to the normal error stream, stderr..

Unlike some Nmap arguments, the space between the logfile option flag

(such as -oX) and the filename or hyphen is mandatory. If you omit the

flags and give arguments such as -oG- or -oXscan.xml, a backwards

compatibility feature of Nmap will cause the creation of normal format

output files named G- and Xscan.xml respectively.

All of these arguments support strftime-like. conversions in the

filename. %H, %M, %S, %m, %d, %y, and %Y are all exactly the same as

in strftime. %T is the same as %H%M%S, %R is the same as %H%M, and %D

is the same as %m%d%y. A % followed by any other character just yields

that character (%% gives you a percent symbol). So -oX ´scan-%T-%D.xml´

will use an XML file in the form of scan-144840-121307.xml.

Nmap also offers options to control scan verbosity and to append to

output files rather than clobbering them. All of these options are

described below.

Nmap Output Formats

-oN filespec (normal output) .

Requests that normal output be directed to the given filename. As

discussed above, this differs slightly from interactive output.

-oX filespec (XML output) .

Requests that XML output be directed to the given filename. Nmap

includes a document type definition (DTD) which allows XML parsers

to validate Nmap XML output. While it is primarily intended for

programmatic use, it can also help humans interpret Nmap XML

output. The DTD defines the legal elements of the format, and often

enumerates the attributes and values they can take on. The latest

version is always available from http://nmap.org/data/nmap.dtd.

XML offers a stable format that is easily parsed by software. Free

XML parsers are available for all major computer languages,

including C/C++, Perl, Python, and Java. People have even written

bindings for most of these languages to handle Nmap output and

execution specifically. Examples are Nmap::Scanner[15] and

Nmap::Parser[16] in Perl CPAN. In almost all cases that a

non-trivial application interfaces with Nmap, XML is the preferred

format.

The XML output references an XSL stylesheet which can be used to

format the results as HTML. The easiest way to use this is simply

to load the XML output in a web browser such as Firefox or IE. By

default, this will only work on the machine you ran Nmap on (or a

similarly configured one) due to the hard-coded nmap.xsl filesystem

path. Use the --webxml or --stylesheet options to create portable

XML files that render as HTML on any web-connected machine.

-oS filespec (ScRipT KIdd|3 oUTpuT) .

Script kiddie output is like interactive output, except that it is

post-processed to better suit the l33t HaXXorZ who previously

looked down on Nmap due to its consistent capitalization and

spelling. Humor impaired people should note that this option is

making fun of the script kiddies before flaming me for supposedly

“helping them”.

-oG filespec (grepable output) .

This output format is covered last because it is deprecated. The

XML output format is far more powerful, and is nearly as convenient

for experienced users. XML is a standard for which dozens of

excellent parsers are available, while grepable output is my own

simple hack. XML is extensible to support new Nmap features as they

are released, while I often must omit those features from grepable

output for lack of a place to put them.

Nevertheless, grepable output is still quite popular. It is a

simple format that lists each host on one line and can be trivially

searched and parsed with standard Unix tools such as grep, awk,

cut, sed, diff, and Perl. Even I usually use it for one-off tests

done at the command line. Finding all the hosts with the SSH port

open or that are running Solaris takes only a simple grep to

identify the hosts, piped to an awk or cut command to print the

desired fields.

Grepable output consists of comments (lines starting with a pound

(#)). and target lines. A target line includes a combination of

six labeled fields, separated by tabs and followed with a colon.

The fields are Host, Ports, Protocols, Ignored State, OS, Seq

Index, IP ID, and Status.

The most important of these fields is generally Ports, which gives

details on each interesting port. It is a comma separated list of

port entries. Each port entry represents one interesting port, and

takes the form of seven slash (/) separated subfields. Those

subfields are: Port number, State, Protocol, Owner, Service, SunRPC

info, and Version info.

As with XML output, this man page does not allow for documenting

the entire format. A more detailed look at the Nmap grepable output

format is available from

http://nmap.org/book/output-formats-grepable-output.html.

-oA basename (Output to all formats) .

As a convenience, you may specify -oA basename to store scan

results in normal, XML, and grepable formats at once. They are

stored in basename.nmap, basename.xml, and basename.gnmap,

respectively. As with most programs, you can prefix the filenames

with a directory path, such as ~/nmaplogs/foocorp/ on Unix or

c:/hacking/sco on Windows.

Verbosity and debugging options

-v (Increase verbosity level) .

Increases the verbosity level, causing Nmap to print more

information about the scan in progress. Open ports are shown as

they are found and completion time estimates are provided when Nmap

thinks a scan will take more than a few minutes. Use it twice or

more for even greater verbosity.

Most changes only affect interactive output, and some also affect

normal and script kiddie output. The other output types are meant

to be processed by machines, so Nmap can give substantial detail by

default in those formats without fatiguing a human user. However,

there are a few changes in other modes where output size can be

reduced substantially by omitting some detail. For example, a

comment line in the grepable output that provides a list of all

ports scanned is only printed in verbose mode because it can be

quite long.

-d [level] (Increase or set debugging level) .

When even verbose mode doesn´t provide sufficient data for you,

debugging is available to flood you with much more! As with the

verbosity option (-v), debugging is enabled with a command-line

flag (-d) and the debug level can be increased by specifying it

multiple times.. Alternatively, you can set a debug level by

giving an argument to -d. For example, -d9 sets level nine. That is

the highest effective level and will produce thousands of lines

unless you run a very simple scan with very few ports and targets.

Debugging output is useful when a bug is suspected in Nmap, or if

you are simply confused as to what Nmap is doing and why. As this

feature is mostly intended for developers, debug lines aren´t

always self-explanatory. You may get something like: Timeout vals:

srtt: -1 rttvar: -1 to: 1000000 delta 14987 ==> srtt: 14987 rttvar:

14987 to: 100000. If you don´t understand a line, your only

recourses are to ignore it, look it up in the source code, or

request help from the development list (nmap-dev).. Some lines are

self explanatory, but the messages become more obscure as the debug

level is increased.

--reason (Host and port state reasons) .

Shows the reason each port is set to a specific state and the

reason each host is up or down. This option displays the type of

the packet that determined a port or hosts state. For example, A

RST packet from a closed port or an echo reply from an alive host.

The information Nmap can provide is determined by the type of scan

or ping. The SYN scan and SYN ping (-sS and -PS) are very detailed,

but the TCP connect scan (-sT) is limited by the implementation of

the connect system call. This feature is automatically enabled by

the debug option (-d). and the results are stored in XML log files

even if this option is not specified.

--stats-every time (Print periodic timing stats) .

Periodically prints a timing status message after each interval of

time. The time is a specification of the kind described in the

section called “TIMING AND PERFORMANCE”; so for example, use

--stats-every 10s to get a status update every 10 seconds. Updates

are printed to interactive output (the screen) and XML output.

--packet-trace (Trace packets and data sent and received) .

Causes Nmap to print a summary of every packet sent or received.

This is often used for debugging, but is also a valuable way for

new users to understand exactly what Nmap is doing under the

covers. To avoid printing thousands of lines, you may want to

specify a limited number of ports to scan, such as -p20-30. If you

only care about the goings on of the version detection subsystem,

use --version-trace instead. If you only care about script tracing,

specify --script-trace. With --packet-trace, you get all of the

above.

--open (Show only open (or possibly open) ports) .

Sometimes you only care about ports you can actually connect to

(open ones), and don´t want results cluttered with closed,

filtered, and closed|filtered ports. Output customization is

normally done after the scan using tools such as grep, awk, and

Perl, but this feature was added due to overwhelming requests.

Specify --open to only see open, open|filtered, and unfiltered

ports. These three ports are treated just as they normally are,

which means that open|filtered and unfiltered may be condensed into

counts if there are an overwhelming number of them.

--iflist (List interfaces and routes) .

Prints the interface list and system routes as detected by Nmap.

This is useful for debugging routing problems or device

mischaracterization (such as Nmap treating a PPP connection as

ethernet).

--log-errors (Log errors/warnings to normal mode output file) .

Warnings and errors printed by Nmap usually go only to the screen

(interactive output), leaving any normal-format output files

(usually specified with -oN) uncluttered. When you do want to see

those messages in the normal output file you specified, add this

option. It is useful when you aren´t watching the interactive

output or when you want to record errors while debugging a problem.

The error and warning messages will still appear in interactive

mode too. This won´t work for most errors related to bad

command-line arguments because Nmap may not have initialized its

output files yet. In addition, some Nmap error and warning messages

use a different system which does not yet support this option.

An alternative to --log-errors is redirecting interactive output

(including the standard error stream) to a file. Most Unix shells

make this approach easy, though it can be difficult on Windows.

Miscellaneous output options

--append-output (Append to rather than clobber output files) .

When you specify a filename to an output format flag such as -oX or

-oN, that file is overwritten by default. If you prefer to keep the

existing content of the file and append the new results, specify

the --append-output option. All output filenames specified in that

Nmap execution will then be appended to rather than clobbered. This

doesn´t work well for XML (-oX) scan data as the resultant file

generally won´t parse properly until you fix it up by hand.

--resume filename (Resume aborted scan) .

Some extensive Nmap runs take a very long time—on the order of

days. Such scans don´t always run to completion. Restrictions may

prevent Nmap from being run during working hours, the network could

go down, the machine Nmap is running on might suffer a planned or

unplanned reboot, or Nmap itself could crash. The administrator

running Nmap could cancel it for any other reason as well, by

pressing ctrl-C. Restarting the whole scan from the beginning may

be undesirable. Fortunately, if normal (-oN) or grepable (-oG) logs

were kept, the user can ask Nmap to resume scanning with the target

it was working on when execution ceased. Simply specify the

--resume option and pass the normal/grepable output file as its

argument. No other arguments are permitted, as Nmap parses the

output file to use the same ones specified previously. Simply call

Nmap as nmap --resume logfilename. Nmap will append new results to

the data files specified in the previous execution. Resumption does

not support the XML output format because combining the two runs

into one valid XML file would be difficult.

--stylesheet path or URL (Set XSL stylesheet to transform XML output) .

Nmap ships with an XSL stylesheet named nmap.xsl for viewing or

translating XML output to HTML. The XML output includes an

xml-stylesheet directive which points to nmap.xml where it was

initially installed by Nmap (or in the current working directory on

Windows). Simply load Nmap´s XML output in a modern web browser and

it should retrieve nmap.xsl from the filesystem and use it to

render results. If you wish to use a different stylesheet, specify

it as the argument to --stylesheet. You must pass the full pathname

or URL. One common invocation is --stylesheet

http://nmap.org/data/nmap.xsl. This tells a browser to load the

latest version of the stylesheet from Nmap.Org. The --webxml option

does the same thing with less typing and memorization. Loading the

XSL from Nmap.Org makes it easier to view results on a machine that

doesn´t have Nmap (and thus nmap.xsl) installed. So the URL is

often more useful, but the local filesystem location of nmap.xsl is

used by default for privacy reasons.

--webxml (Load stylesheet from Nmap.Org) .

This convenience option is simply an alias for --stylesheet

http://nmap.org/data/nmap.xsl.

--no-stylesheet (Omit XSL stylesheet declaration from XML) .

Specify this option to prevent Nmap from associating any XSL

stylesheet with its XML output. The xml-stylesheet directive is

omitted.

MISCELLANEOUS OPTIONS

This section describes some important (and not-so-important) options

that don´t really fit anywhere else.

-6 (Enable IPv6 scanning) .

Since 2002, Nmap has offered IPv6 support for its most popular

features. In particular, ping scanning (TCP-only), connect

scanning, and version detection all support IPv6. The command

syntax is the same as usual except that you also add the -6 option.

Of course, you must use IPv6 syntax if you specify an address

rather than a hostname. An address might look like

3ffe:7501:4819:2000:210:f3ff:fe03:14d0, so hostnames are

recommended. The output looks the same as usual, with the IPv6

address on the “interesting ports” line being the only IPv6 give

away.

While IPv6 hasn´t exactly taken the world by storm, it gets

significant use in some (usually Asian) countries and most modern

operating systems support it. To use Nmap with IPv6, both the

source and target of your scan must be configured for IPv6. If your

ISP (like most of them) does not allocate IPv6 addresses to you,

free tunnel brokers are widely available and work fine with Nmap. I

use the free IPv6 tunnel broker. service at

http://www.tunnelbroker.net. Other tunnel brokers are listed at

Wikipedia[17]. 6to4 tunnels are another popular, free approach.

-A (Aggressive scan options) .

This option enables additional advanced and aggressive options. I

haven´t decided exactly which it stands for yet. Presently this

enables OS detection (-O), version scanning (-sV), script scanning

(-sC) and traceroute (--traceroute). More features may be added in

the future. The point is to enable a comprehensive set of scan

options without people having to remember a large set of flags.

However, because script scanning with the default set is considered

intrusive, you should not use -A against target networks without

permission. This option only enables features, and not timing

options (such as -T4) or verbosity options (-v) that you might want

as well.

--datadir directoryname (Specify custom Nmap data file location) .

Nmap obtains some special data at runtime in files named

nmap-service-probes, nmap-services, nmap-protocols, nmap-rpc,

nmap-mac-prefixes, and nmap-os-db. If the location of any of these

files has been specified (using the --servicedb or --versiondb

options), that location is used for that file. After that, Nmap

searches these files in the directory specified with the --datadir

option (if any). Any files not found there, are searched for in the

directory specified by the NMAPDIR environmental variable.

~/.nmap. for real and effective UIDs (POSIX systems only) or

location of the Nmap executable (Win32 only), and then a

compiled-in location such as /usr/local/share/nmap or

/usr/share/nmap . As a last resort, Nmap will look in the current

directory.

--servicedb services file (Specify custom services file) .

Asks Nmap to use the specified services file rather than the

nmap-services data file that comes with Nmap. Using this option

also causes a fast scan (-F) to be used. See the description for

--datadir for more information on Nmap´s data files.

--versiondb service probes file (Specify custom service probes file) .

Asks Nmap to use the specified service probes file rather than the

nmap-service-probes data file that comes with Nmap. See the

description for --datadir for more information on Nmap´s data

files.

--send-eth (Use raw ethernet sending) .

Asks Nmap to send packets at the raw ethernet (data link) layer

rather than the higher IP (network) layer. By default, Nmap chooses

the one which is generally best for the platform it is running on.

Raw sockets (IP layer). are generally most efficient for Unix

machines, while ethernet frames are required for Windows operation

since Microsoft disabled raw socket support. Nmap still uses raw IP

packets on Unix despite this option when there is no other choice

(such as non-ethernet connections).

--send-ip (Send at raw IP level) .

Asks Nmap to send packets via raw IP sockets rather than sending

lower level ethernet frames. It is the complement to the --send-eth

option discussed previously.

--privileged (Assume that the user is fully privileged) .

Tells Nmap to simply assume that it is privileged enough to perform

raw socket sends, packet sniffing, and similar operations that

usually require root privileges. on Unix systems. By default Nmap

quits if such operations are requested but geteuid is not zero.

--privileged is useful with Linux kernel capabilities and similar

systems that may be configured to allow unprivileged users to

perform raw-packet scans. Be sure to provide this option flag

before any flags for options that require privileges (SYN scan, OS

detection, etc.). The NMAP_PRIVILEGED. environmental variable may

be set as an equivalent alternative to --privileged.

--unprivileged (Assume that the user lacks raw socket privileges) .

This option is the opposite of --privileged. It tells Nmap to treat

the user as lacking network raw socket and sniffing privileges.

This is useful for testing, debugging, or when the raw network

functionality of your operating system is somehow broken. The

NMAP_UNPRIVILEGED. environmental variable may be set as an

equivalent alternative to --unprivileged.

--release-memory (Release memory before quitting) .

This option is only useful for memory-leak debugging. It causes

Nmap to release allocated memory just before it quits so that

actual memory leaks are easier to spot. Normally Nmap skips this as

the OS does this anyway upon process termination.

--interactive (Start in interactive mode) .

Starts Nmap in interactive mode, which offers an interactive Nmap

prompt allowing easy launching of multiple scans (either

synchronously or in the background). This is useful for people who

scan from multi-user systems as they often want to test their

security without letting everyone else on the system know exactly

which systems they are scanning. Use --interactive to activate this

mode and then type h for help. This option is rarely used because

proper shells are usually more familiar and feature-complete. This

option includes a bang (!) operator for executing shell commands,

which is one of many reasons not to install Nmap setuid root..

-V; --version (Print version number) .

Prints the Nmap version number and exits.

-h; --help (Print help summary page) .

Prints a short help screen with the most common command flags.

Running Nmap without any arguments does the same thing.

RUNTIME INTERACTION

During the execution of Nmap, all key presses are captured. This allows

you to interact with the program without aborting and restarting it.

Certain special keys will change options, while any other keys will

print out a status message telling you about the scan. The convention

is that lowercase letters increase the amount of printing, and

uppercase letters decrease the printing. You may also press ‘?’ for

help.

v / V

Increase / decrease the verbosity level

d / D

Increase / decrease the debugging Level

p / P

Turn on / off packet tracing

?

Print a runtime interaction help screen

Anything else

Print out a status message like this:

Stats: 0:00:08 elapsed; 111 hosts completed (5 up), 5 undergoing

Service Scan

Service scan Timing: About 28.00% done; ETC: 16:18 (0:00:15

remaining)

EXAMPLES

Here are some Nmap usage examples, from the simple and routine to a

little more complex and esoteric. Some actual IP addresses and domain

names are used to make things more concrete. In their place you should

substitute addresses/names from your own network.. While I don´t think

port scanning other networks is or should be illegal, some network

administrators don´t appreciate unsolicited scanning of their networks

and may complain. Getting permission first is the best approach.

For testing purposes, you have permission to scan the host

scanme.nmap.org. This permission only includes scanning via Nmap and

not testing exploits or denial of service attacks. To conserve

bandwidth, please do not initiate more than a dozen scans against that

host per day. If this free scanning target service is abused, it will

be taken down and Nmap will report Failed to resolve given hostname/IP:

scanme.nmap.org. These permissions also apply to the hosts

scanme2.nmap.org, scanme3.nmap.org, and so on, though those hosts do

not currently exist.

nmap -v scanme.nmap.org

This option scans all reserved TCP ports on the machine scanme.nmap.org

. The -v option enables verbose mode.

nmap -sS -O scanme.nmap.org/24

Launches a stealth SYN scan against each machine that is up out of the

256 IPs on “class C” sized network where Scanme resides. It also tries

to determine what operating system is running on each host that is up

and running. This requires root privileges because of the SYN scan and

OS detection.

nmap -sV -p 22,53,110,143,4564 198.116.0-255.1-127

Launches host enumeration and a TCP scan at the first half of each of

the 255 possible eight-bit subnets in the 198.116 class B address

space. This tests whether the systems run SSH, DNS, POP3, or IMAP on

their standard ports, or anything on port 4564. For any of these ports

found open, version detection is used to determine what application is

running.

nmap -v -iR 100000 -PN -p 80

Asks Nmap to choose 100,000 hosts at random and scan them for web

servers (port 80). Host enumeration is disabled with -PN since first

sending a couple probes to determine whether a host is up is wasteful

when you are only probing one port on each target host anyway.

nmap -PN -p80 -oX logs/pb-port80scan.xml -oG logs/pb-port80scan.gnmap

216.163.128.20/20

This scans 4096 IPs for any web servers (without pinging them) and

saves the output in grepable and XML formats.

NMAP BOOK

While this reference guide details all material Nmap options, it can´t

fully demonstrate how to apply those features to quickly solve

real-world tasks. For that, we released Nmap Network Scanning: The

Official Nmap Project Guide to Network Discovery and Security Scanning.

Topics include subverting firewalls and intrusion detection systems,

optimizing Nmap performance, and automating common networking tasks

with the Nmap Scripting Engine. Hints and instructions are provided for

common Nmap tasks such as taking network inventory, penetration

testing, detecting rogue wireless access points, and quashing network

worm outbreaks. Examples and diagrams show actual communication on the

wire. More than half of the book is available free online. See

http://nmap.org/book for more information.

BUGS

Like its author, Nmap isn´t perfect. But you can help make it better by

sending bug reports or even writing patches. If Nmap doesn´t behave the

way you expect, first upgrade to the latest version available from

http://nmap.org. If the problem persists, do some research to determine

whether it has already been discovered and addressed. Try searching for

the error message on our search page at http://insecure.org/search.html

or at Google. Also try browsing the nmap-dev archives at

http://seclists.org/.. Read this full manual page as well. If nothing

comes of this, mail a bug report to [email protected]. Please

include everything you have learned about the problem, as well as what

version of Nmap you are running and what operating system version it is

running on. Problem reports and Nmap usage questions sent to

[email protected] are far more likely to be answered than those

sent to Fyodor directly. If you subscribe to the nmap-dev list before

posting, your message will bypass moderation and get through more

quickly. Subscribe at

http://cgi.insecure.org/mailman/listinfo/nmap-dev.

Code patches to fix bugs are even better than bug reports. Basic

instructions for creating patch files with your changes are available

at http://nmap.org/data/HACKING. Patches may be sent to nmap-dev

(recommended) or to Fyodor directly.

AUTHOR

Gordon “Fyodor” Lyon [email protected] (http://insecure.org)

Hundreds of people have made valuable contributions to Nmap over the

years. These are detailed in the CHANGELOG. file which is distributed

with Nmap and also available from http://nmap.org/changelog.html.

LEGAL NOTICES

Nmap Copyright and Licensing

The Nmap Security Scanner is (C) 1996–2009 Insecure.Com LLC. Nmap is

also a registered trademark of Insecure.Com LLC. This program is free

software; you may redistribute and/or modify it under the terms of the

GNU General Public License as published by the Free Software

Foundation; Version 2 with the clarifications and exceptions described

below. This guarantees your right to use, modify, and redistribute this

software under certain conditions. If you wish to embed Nmap technology

into proprietary software, we sell alternative licenses (contact

[email protected]). Dozens of software vendors already license Nmap

technology such as host discovery, port scanning, OS detection, and

version detection.

Note that the GPL places important restrictions on “derived works”, yet

it does not provide a detailed definition of that term. To avoid

misunderstandings, we consider an application to constitute a

“derivative work” for the purpose of this license if it does any of the

following:

· Integrates source code from Nmap

· Reads or includes Nmap copyrighted data files, such as nmap-os-db

or nmap-service-probes.

· Executes Nmap and parses the results (as opposed to typical shell

or execution-menu apps, which simply display raw Nmap output and so

are not derivative works.)

· Integrates/includes/aggregates Nmap into a proprietary executable

installer, such as those produced by InstallShield.

· Links to a library or executes a program that does any of the

above.

The term “Nmap” should be taken to also include any portions or derived

works of Nmap. This list is not exclusive, but is meant to clarify our

interpretation of derived works with some common examples. Our

interpretation applies only to Nmap—we don´t speak for other people´s

GPL works.

If you have any questions about the GPL licensing restrictions on using

Nmap in non-GPL works, we would be happy to help. As mentioned above,

we also offer alternative license to integrate Nmap into proprietary

applications and appliances. These contracts have been sold to many

security vendors, and generally include a perpetual license as well as

providing for priority support and updates as well as helping to fund

the continued development of Nmap technology. Please email

[email protected] for further information.

As a special exception to the GPL terms, Insecure.Com LLC grants

permission to link the code of this program with any version of the

OpenSSL library which is distributed under a license identical to that

listed in the included COPYING.OpenSSL file, and distribute linked

combinations including the two.. You must obey the GNU GPL in all

respects for all of the code used other than OpenSSL. If you modify

this file, you may extend this exception to your version of the file,

but you are not obligated to do so.

If you received these files with a written license agreement or

contract stating terms other than the terms above, then that

alternative license agreement takes precedence over these comments.

Creative Commons License for this Nmap Guide

This Nmap Reference Guide is (C) 2005–2009 Insecure.Com LLC. It is

hereby placed under version 3.0 of the Creative Commons Attribution

License[18]. This allows you redistribute and modify the work as you

desire, as long as you credit the original source. Alternatively, you

may choose to treat this document as falling under the same license as

Nmap itself (discussed previously).

Source Code Availability and Community Contributions

Source is provided to this software because we believe users have a

right to know exactly what a program is going to do before they run it.

This also allows you to audit the software for security holes (none

have been found so far).

Source code also allows you to port Nmap to new platforms, fix bugs,

and add new features. You are highly encouraged to send your changes to

[email protected] for possible incorporation into the main

distribution. By sending these changes to Fyodor or one of the

Insecure.Org development mailing lists, it is assumed that you are

offering the Nmap Project (Insecure.Com LLC) the unlimited,

non-exclusive right to reuse, modify, and relicense the code. Nmap will

always be available Open Source,. but this is important because the

inability to relicense code has caused devastating problems for other

Free Software projects (such as KDE and NASM). We also occasionally

relicense the code to third parties as discussed above. If you wish to

specify special license conditions of your contributions, just say so

when you send them.

No Warranty.

This program is distributed in the hope that it will be useful, but

WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU

General Public License v2.0 for more details at

http://www.gnu.org/licenses/gpl-2.0.html, or in the COPYING file

included with Nmap.

It should also be noted that Nmap has occasionally been known to crash

poorly written applications, TCP/IP stacks, and even operating

systems.. While this is extremely rare, it is important to keep in

mind. Nmap should never be run against mission critical systems unless

you are prepared to suffer downtime. We acknowledge here that Nmap may

crash your systems or networks and we disclaim all liability for any

damage or problems Nmap could cause.

Inappropriate Usage

Because of the slight risk of crashes and because a few black hats like

to use Nmap for reconnaissance prior to attacking systems, there are

administrators who become upset and may complain when their system is

scanned. Thus, it is often advisable to request permission before doing

even a light scan of a network.

Nmap should never be installed with special privileges (e.g. suid root)

for security reasons..

Third-Party Software

This product includes software developed by the Apache Software

Foundation[19]. A modified version of the Libpcap portable packet

capture library[20]. is distributed along with Nmap. The Windows

version of Nmap utilized the Libpcap-derived WinPcap library[21].

instead. Regular expression support is provided by the PCRE

library[22],. which is open-source software, written by Philip Hazel..

Certain raw networking functions use the Libdnet[23]. networking

library, which was written by Dug Song.. A modified version is

distributed with Nmap. Nmap can optionally link with the OpenSSL

cryptography toolkit[24]. for SSL version detection support. The Nmap

Scripting Engine uses an embedded version of the Lua programming

language[25].. All of the third-party software described in this

paragraph is freely redistributable under BSD-style software licenses.

United States Export Control.

Nmap only uses encryption when compiled with the optional OpenSSL

support and linked with OpenSSL. When compiled without OpenSSL support,

Insecure.Com LLC believes that Nmap is not subject to U.S. Export

Administration Regulations (EAR)[26] export control. As such, there is

no applicable ECCN (explort control classification number) and

exportation does not require any special license, permit, or other

governmental authorization.

When compiled with OpenSSL support or distributed as source code,

Insecure.Com LLC believes that Nmap falls under U.S. ECCN 5D002[27]

(“Information Security Software”). We distribute Nmap under the TSU

exception for publicly available encryption software defined in EAR

740.13(e)[28].

NOTES

1. Nmap Network Scanning: The Official Nmap Project Guide to Network

Discovery and Security Scanning

http://nmap.org/book/

2. RFC 1122

http://www.rfc-editor.org/rfc/rfc1122.txt

3. RFC 792

http://www.rfc-editor.org/rfc/rfc792.txt

4. RFC 950

http://www.rfc-editor.org/rfc/rfc950.txt

5. RFC 1918

http://www.rfc-editor.org/rfc/rfc1918.txt

6. UDP

http://www.rfc-editor.org/rfc/rfc768.txt

7. SCTP

http://www.rfc-editor.org/rfc/rfc4960.txt

8. TCP RFC

http://www.rfc-editor.org/rfc/rfc793.txt

9. RFC 959

http://www.rfc-editor.org/rfc/rfc959.txt

10. RFC 1323

http://www.rfc-editor.org/rfc/rfc1323.txt

11. Lua programming language

http://lua.org

12. precedence

http://www.lua.org/manual/5.1/manual.html#2.5.3

13. IP protocol

http://www.rfc-editor.org/rfc/rfc791.txt

14. RFC 2960

http://www.rfc-editor.org/rfc/rfc2960.txt

15. Nmap::Scanner

http://sourceforge.net/projects/nmap-scanner/

16. Nmap::Parser

http://nmapparser.wordpress.com/

17. listed at Wikipedia

http://en.wikipedia.org/wiki/List_of_IPv6_tunnel_brokers

18. Creative Commons Attribution License

http://creativecommons.org/licenses/by/3.0/

19. Apache Software Foundation

http://www.apache.org

20. Libpcap portable packet capture library

http://www.tcpdump.org

21. WinPcap library

http://www.winpcap.org

22. PCRE library

http://www.pcre.org

23. Libdnet

http://libdnet.sourceforge.net

24. OpenSSL cryptography toolkit

http://www.openssl.org

25. Lua programming language

http://www.lua.org

26. Export Administration Regulations (EAR)

http://www.access.gpo.gov/bis/ear/ear_data.html

27. 5D002

http://www.access.gpo.gov/bis/ear/pdf/ccl5-pt2.pdf

28. EAR 740.13(e)

http://www.access.gpo.gov/bis/ear/pdf/740.pdf

Nmap 01/26/2010 NMAP(1)