Iptables 基本设置指南

目录

Basic Commands 基本命令

Allowing Established Sessions 允许已建立的连接接收数据

Allowing Incoming Traffic on Specific Ports 开放指定的端口

Blocking Traffic 阻断通信

Editing iptables 编辑iptables

Logging 记录

Saving iptables 保存设置

Configuration on startup 开机自动加载配置

Tips 技巧

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Basic Commands 基本命令

进入iptables

# sudo iptables -L

列出目前的ip策略. 如果您刚刚配置好服务器,您是没有设置ip规则的，您要自己设置。

Chain INPUT (policy ACCEPT)
target     prot opt source               destination
Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

使用命令

# sudo iptables -L

查看现有的iptables防火墙规则。如果您刚架设好服务器，那么规则表应该是空的，您将看到如下内容

Chain INPUT (policy ACCEPT)
target     prot opt source               destination
Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

Allowing Established Sessions 允许已建立的连接接收数据

We can allow established sessions to receive traffic:

可以使用下面的命令，允许已建立的连接接收数据：

# iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

Allowing Incoming Traffic on Specific Ports 开放指定的端口

You could start by blocking traffic, but you might be working over SSH, where you would need to allow SSH before blocking everything else.

To allow incoming traffic on port 22 (traditionally used by SSH), you could tell iptables to allow all TCP traffic on port 22 of your network adapter.

刚开始时您不妨阻断所有通信，但考虑到您将来可能要使用SSH，那么您要让iptables在使用默认规则丢弃报文之前，允许SSH报文通过。

要开放端口22（SSH的默认端口），您要告诉iptables允许接受到的所有目标端口为22的TCP报文通过。

# iptables -A INPUT -p tcp -i eth0 --dport ssh -j ACCEPT

Specifically, this appends (-A) to the table INPUT the rule that any traffic to the interface (-i) eth0 on the destination port for ssh that iptables should jump (-j), or perform the action, ACCEPT.

执行上面的命令，一条规则会被追加到INPUT规则表的末尾（-A表示追加）。根据这条规则，对所有从接口eth0（-i指出对通过哪个接口的报文运用此规则）接收到的目标端口为22的报文，iptables要执行ACCEPT行动（-j指明当报文与规则相匹配时应采取的行动）。

Lets check the rules: (only the first few lines shown, you will see more)

我们来看看规则表中的情况：（这里只列出了开始的几行，您应该会看到更多内容）

# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere            state RELATED,ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ssh

Now, let's allow all web traffic

现在我们开放端口80：

# iptables -A INPUT -p tcp -i eth0 --dport 80 -j ACCEPT

Checking our rules, we have

此时的规则表中的内容如下：

# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere            state RELATED,ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ssh
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:www

We have specifically allowed tcp traffic to the ssh and web ports, but as we have not blocked anything, all traffic can still come in.

通过上述命令，我们已经代开了SSH和web服务的相应的端口，但由于没有阻断任何通信，因此所有的报文都能通过。

Blocking Traffic 阻断通信

Once a decision is made about a packet, no more rules affect it. As our rules allowing ssh and web traffic come first, as long as our rule to block all traffic comes after them, we can still accept the traffic we want. All we need to do is put the rule to block all traffic at the end. The -A command tells iptables to append the rule at the end, so we'll use that again.

对每一个报文，iptables依次测试每一条规则，看报文与规则是否相匹配。一旦找到一条匹配的规则，就根据此规则中指定的行动，对报文进行处置，而对后面的规则不再进行测试。因此，如果我们在规则表的末尾添加一条规则，让iptables丢弃所有报文，但由于有了前面几条规则，ssh和web的正常通信不会受到影响。

sudo iptables -A INPUT -j DROP

# iptables -A INPUT -j DROP
# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere            state RELATED,ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ssh
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:www
DROP       all  --  anywhere             anywhere

Because we didn't specify an interface or a protocol, any traffic for any port on any interface is blocked, except for web and ssh.

在上面的规则中，没有明确指出针对哪个接口或哪种协议使用此规则，所以从每个接口接收到的除ssh和web之外的所有报文都会被丢弃，因为规则的读取是从上面的链开始往下读的。

Editing iptables 编辑iptables

The only problem with our setup so far is that even the loopback port is blocked. We could have written the drop rule for just eth0 by specifying -i eth0, but we could also add a rule for the loopback. If we append this rule, it will come too late - after all the traffic has been dropped. We need to insert this rule onto the fourth line.

进行至此，仍有一个问题，就是环回接口也被阻断了。刚才添加DROP规则的时候其实就可以使用-i eth0来解决这一问题。然而我们也可以为环回接口添加一条新规则来解决这个问题。但是不能将新规则追加到末尾，因为前一条规则已经把所有报文都丢弃了，而应该把它插到DROP规则前面，即规则表中第四行的位置。

# iptables -I INPUT 4 -i lo -j ACCEPT
# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere            state RELATED,ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ssh
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:www
ACCEPT     all  --  anywhere             anywhere
DROP       all  --  anywhere             anywhere

The last two lines look nearly the same, so we will list iptables in greater detail.

规则表中的最后两行几乎一样，为了看看它们到底有什么不同，我们可以使用

# iptables -L -v

Logging 记录

In the above examples none of the traffic will be logged. If you would like to log dropped packets to syslog, this would be the quickest way:

在前面的例子中，没有任何报文会被记录到日志中。如果您希望将被丢弃的报文记录到syslog中，最简单的方法是：

# iptables -I INPUT 5 -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7

See Tips section for more ideas on logging.

更多关于日志记录的信息，请参照Tips(技巧)这一节。

Saving iptables 保存设置

If you were to reboot your machine right now, your iptables configuration would disapear. Rather than type this each time you reboot, however, you can save the configuration, and have it start up automatically. To save the configuration, you can use iptables-save and iptables-restore.

机器重启后，iptables中的配置信息会被清空。您可以将这些配置保存下来，让iptables在启动时自动加载，省得每次都得重新输入。iptables-save和iptables-restore 是用来保存和恢复设置的。

Configuration on startup 开机自动加载配置

Save your firewall rules to a file

先将防火墙规则保存到/etc/iptables.up.rules文件中

# iptables-save > /etc/iptables.up.rules

Then modify the /etc/network/interfaces script to apply the rules automatically (the bottom line is added)

然后修改脚本/etc/network/interfaces，使系统能自动应用这些规则（最后一行是我们手工添加的）。

auto eth0
iface eth0 inet dhcp
pre-up iptables-restore < /etc/iptables.up.rules

You can also prepare a set of down rules and apply it automatically

当网络接口关闭后，您可以让iptables使用一套不同的规则集。

auto eth0
iface eth0 inet dhcp
pre-up iptables-restore < /etc/iptables.up.rules
post-down iptables-restore < /etc/iptables.down.rules

Tips 技巧

If you manually edit iptables on a regular basis 如果你经常手动编辑iptables

The above steps go over how to setup your firewall rules and presume they will be relatively static (and for most people they should be). But if you do a lot of development work, you may want to have your iptables saved everytime you reboot. You could add a line like this one in /etc/network/interfaces:

大多数人并不需要经常改变他们的防火墙规则，因此只要根据前面的介绍，建立起防火墙规则就可以了。但是如果您要经常修改防火墙规则，以使其更加完善，那么您可能希望系统在每次重启前将防火墙的设置保存下来。为此您可以在/etc/network/interfaces文件中添加一行：

pre-up iptables-restore < /etc/iptables.up.rules
post-down iptables-save > /etc/iptables.up.rules

The line "post-down iptables-save > /etc/iptables.up.rules" will save the rules to be used on the next boot.

"post-down iptables-save > /etc/iptables.up.rules"会将设置保存下来，以便下次启动时使用。

Using iptables-save/restore to test rules 使用iptables-save/restore测试规则

If you edit your iptables beyond this tutorial, you may want to use the iptables-save and iptables-restore feature to edit and test your rules. To do this open the rules file in your favorite text editor (in this example gedit).

使用iptables-save和iptables-restore可以很方便地修改和测试防火墙规则。首先运行iptables-save将规则保存到一个文件，然后用编辑器编辑该文件。

# iptables-save > /etc/iptables.test.rules
# gedit /etc/iptables.test.rules

You will have a file that appears similiar to (following the example above):

如果您根据前面的例子建立了防火墙规则，iptables-save将产生一个类似于如下内容的文件：

# Generated by iptables-save v1.3.1 on Sun Apr 23 06:19:53 2006
*filter
:INPUT ACCEPT [368:102354]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [92952:20764374]
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -i eth0 -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -i eth0 -p tcp -m tcp --dport 80 -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7
-A INPUT -j DROP
COMMIT
# Completed on Sun Apr 23 06:19:53 2006

Notice that these are iptables commands minus the iptable command. Feel free to edit this to file and save when complete. Then to test simply:

文件内容其实就是各种iptables命令，只不过把命令名iptables省略了。您可以随意对这个文件进行编辑，然后保存。接着使用以下命令测试修改后的规则：

# iptables-restore < /etc/iptables.test.rules

After testing, if you have not added the iptables-save command above to your /etc/network/interfaces remember not to lose your changes:

之前您如果没有在/etc/network/interfaces文件中添加iptables-save命令，那么测试之后，别忘了把您所作的修改保存起来。

# iptables-save > /etc/iptables.up.rules

More detailed Logging 关于日志记录的更多细节

For further detail in your syslog you may want create an additional Chain. This will be a very brief example of my /etc/iptables.up.rules showing how I setup my iptables to log to syslog:

您可以创建额外的规则链，以便在syslog中作更加详细的记录。以下是我/etc/iptables.up.rules文件中的一个简单例子：

# Generated by iptables-save v1.3.1 on Sun Apr 23 05:32:09 2006
*filter
:INPUT ACCEPT [273:55355]
:FORWARD ACCEPT [0:0]
:LOGNDROP - [0:0]
:OUTPUT ACCEPT [92376:20668252]
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -i eth0 -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -i eth0 -p tcp -m tcp --dport 80 -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -j LOGNDROP
-A LOGNDROP -p tcp -m limit --limit 5/min -j LOG --log-prefix "Denied TCP: " --log-level 7
-A LOGNDROP -p udp -m limit --limit 5/min -j LOG --log-prefix "Denied UDP: " --log-level 7
-A LOGNDROP -p icmp -m limit --limit 5/min -j LOG --log-prefix "Denied ICMP: " --log-level 7
-A LOGNDROP -j DROP
COMMIT
# Completed on Sun Apr 23 05:32:09 2006

Note a new CHAIN called LOGNDROP at the top of the file. Also, the standard DROP at the bottom of the INPUT chain is replaceed with LOGNDROP and add protocol descriptions so it makes sense looking at the log. Lastly we drop the traffic at the end of the LOGNDROP chain. The following gives some idea of what is happening:

• --limit sets the number of times to log the same rule to syslog
• --log-prefix "Denied..." adds a prefix to make finding in the syslog easier
• --log-level 7 sets the syslog level to informational (see man syslog for more detail, but you can probably leave this)

可以看到，文件前面多了一条名为LOGNDROP的规则链。此外，INPUT链最后一条规则中的DROP被LONGDROP替代。并且在后面我添加了一些内容来描述报文所使用的协议，这可以让记录更容易理解。最后，在LOGNDROP链的末尾，报文被丢弃。

• --limit 对由此规则引发的记录事件的频率进行限制。
• --log-prefix "Denied..." 在每条记录前加上一个前缀，以便查找。
• --log-level 7 将记录的详细程度设为“informational”等级（详情请见man syslog，您也可以直接使用此处的设置）。

Disabling the firewall 禁用防火墙

If you need to disable the firewall temporarily, you can flush all the rules using

可以通过清除所有规则来暂时停止防火墙： (警告：这只适合在没有配置防火墙的环境中，如果已经配置过默认规则为deny的环境，此步骤将使系统的所有网络访问中断)

# sudo iptables -F