DHCP服务部署

DHCP服务部署

一. 简介

    动态主机设置协议（英语：Dynamic Host Configuration Protocol，缩写：DHCP）是一个用于局域网的网络协议，位于OSI模型的应用层，使用UDP协议工作。

二. 用途及功能

    •  用于内部网或网络服务供应商自动分配IP地址给用户
    •  用于内部网管理员作为对所有计算机作中央管理的手段
    •  可分配网卡的IP地址，子网掩码，网络地址，广播地址，默认网关，DNS，引导文件，TFTP（pxe kickstart无人值守时用）

三. 原理+示意图

1. 原理

      DHCP客户端第一次登陆时，由于没有IP，它会以UDP的67端口广播发送Discover（源0.0.0.0 目标 255.255.255.255），一秒内没有应答会以1，3，5，7，9+1-2000ms的延迟重发Discovery包，DHCP服务器收到请求后，以UDP的68端口发起offer包（源DHCP服务器IP 目标0.0.0.0， 包中包含IP，子网掩码，租期等信息 # Discover中包含Client的MAC地址）。
      DHCP服务器通过ICMP协议测试准备分发的IP是否被占用，Client发送Request包(源0.0.0.0 目标255.255.255.255包中包含Client的MAC地址，接受租约的IP地址，提供租约的DHCP服务器地址)，DHCP发起ACK回包（原地址 DHCP服务器地址 目标地址0.0.0.0 包中包含这一IP地址的合法租用以及其他的配置信息）。
      租约问题：用到50%的时候会向服务器发起续约请求，如果服务器未响应，用到75%时，再次请求续约，如果仍未响应，则用到100%后，再次广播发送Discover包。
      Client获取IP成功后，如果网卡断了，再次连接时，IP若被占用，则重新发起Discover包，否则将原来的IP地址继续使用。

2. 示意图

四. 实战搭建

相关文件

服务名 : dhcpd dhcrelay
主配置文件 /etc/dhcp/dhcpd.conf
模板文件 /usr/share/doc/dhcp-*/dhcpd.conf.simple
中继配置文件 /etc/sysconfig/dhcrelay
端口 udp 67 68

配置基础DHCP服务器

1. 实验环境

机器	master	slave1	slave2
作用	DHCP服务端	客户端	客户端
IP地址	192.168.32.80	192.168.32.81	192.168.32.82

2. 步骤

(1). master机器配置yum源，安装dhcp包

[root@master ~]# yum install -y dhcp

(2). 复制模板文件并且覆盖原有配置文件

[root@master ~]# cp -a /usr/share/doc/dhcp-4.1.1/dhcpd.conf.sample /etc/dhcp/dhcpd.conf

(3). 修改配置文件并重启dhcp服务

[root@master ~]# vim /etc/dhcp/dhcpd.conf

    subnet 192.168.32.0 netmask 255.255.255.0 {     # subnet指定一个网段 netmask 指定子网掩码
    range 192.168.32.20 192.168.32.30;                      # range指定自动分配的ip子网为20-30段
    option domain-name-servers 114.114.114.114,8.8.8.8;  # 指定dns服务器
    option routers 192.168.32.1;                                 # 指定网关
    default-lease-time 600;                                         # 默认租约时间
    max-lease-time 7200;                                            # 最大租约时间
}

[root@master ~]# service dhcpd restart
关闭 dhcpd： [确定]
正在启动 dhcpd： [确定]

(4). 修改slave1、slave2网卡配置文件

[root@slave1 ~]# vim /etc/sysconfig/network-scripts/ifcfg-eth0

    DEVICE=eth0
    TYPE=Ethernet
    UUID=021f0b15-fc52-4e9f-912f-4bf79963fab5
    ONBOOT=yes
    NM_CONTROLLED=yes
    BOOTPROTO=dhcp
    HWADDR=00:0C:29:B1:18:8D
    DEFROUTE=yes
    IPV4_FAILURE_FATAL=yes
    IPV6INIT=no
    NAME="System eth0"

slave2同理，将BOOTPROTO改成dhcp
slave1 结果如下:

slave2结果如下:

配置DHCP保留地址

(1). 修改master的dhcp配置文件

[root@master ~]# vim /etc/dhcp/dhcpd.conf

    host fantasia {
      hardware ethernet 00:0C:29:6D:13:A4;
      fixed-address 192.168.32.22;
    }
    host newhost {
      hardware ethernet 00:0C:29:B1:18:8D;
      fixed-address 192.168.32.23;
    }

(2). 客户机重启网络查看mac和ip对应关系

slave1:

slave2:

配置DHCP超级作用域

1. 定义超级作用域

    解决DHCP单个作用域中IP地址不足的情况，比如公司中有300台机器需要配置dhcp自动获取ip，而一个C类IP只有251个可用地址（抛去网关，头尾，dhcp服务器IP），此时需要配置dhcp超级作用域以分配IP不足问题。

2. 配置超级作用域
[root@master ~]# vim /etc/dhcp/dhcpd.conf

    # dhcpd.conf
    #
    # Sample configuration file for ISC dhcpd
    #

    # option definitions common to all supported networks...
    option domain-name "example.org";
    option domain-name-servers ns1.example.org, ns2.example.org;

    default-lease-time 600;
    max-lease-time 7200;

    # Use this to enble / disable dynamic dns updates globally.
    #ddns-update-style none;

    # If this DHCP server is the official DHCP server for the local
    # network, the authoritative directive should be uncommented.
    #authoritative;

    # Use this to send dhcp log messages to a different log file (you also
    # have to hack syslog.conf to complete the redirection).
    log-facility local7;

    # No service will be given on this subnet, but declaring it helps the 
    # DHCP server to understand the network topology.


    # Hosts which require special configuration options can be listed in
    # host statements.   If no address is specified, the address will be
    # allocated dynamically (if possible), but the host-specific information
    # will still come from the host declaration.

    host passacaglia {
      hardware ethernet 0:0:c0:5d:bd:95;
      filename "vmunix.passacaglia";
      server-name "toccata.fugue.com";
    }

    # Fixed IP addresses can also be specified for hosts.   These addresses
    # should not also be listed as being available for dynamic assignment.
    # Hosts for which fixed IP addresses have been specified can boot using
    # BOOTP or DHCP.   Hosts for which no fixed address is specified can only
    # be booted with DHCP, unless there is an address range on the subnet
    # to which a BOOTP client is connected which has the dynamic-bootp flag
    # set.

    # You can declare a class of clients and then do address allocation
    # based on that.   The example below shows a case where all clients
    # in a certain class get addresses on the 10.17.224/24 subnet, and all
    # other clients get addresses on the 10.0.29/24 subnet.

    class "foo" {
      match if substring (option vendor-class-identifier, 0, 4) = "SUNW";
    }
    --------------------------------------------------------------------------
    shared-network 224-29 {
    subnet 192.168.32.0 netmask 255.255.255.0 {
      range 192.168.32.20 192.168.32.20;
      option domain-name-servers 114.114.114.114,8.8.8.8;
      option routers 192.168.32.1;
      default-lease-time 600;
      max-lease-time 7200;
    }
    subnet 192.168.33.0 netmask 255.255.255.0 {
      range 192.168.33.20 192.168.33.20;
      option domain-name-servers 114.114.114.114,8.8.8.8;
      option routers 192.168.33.1;
      default-lease-time 600;
      max-lease-time 7200;
    }
    }
    ---------------------------------------------------------------------------

slave1回显如下:

slave2回显如下:

注意!! 此时 slave1和slave2机器是ping不通的，因为网段不同，所以将采用单臂路由的方式让其通信-------dhcp中继。

配置DHCP中继

1. 实验环境

表格里未填写的代表自动获取,“--”代表不需要配置

机器	master	slave1	slave2	slave3
网卡配置	vm1	vm1	vm1 vm2	vm2
作用	DHCP服务器	DHCP客户端	DHCP 中继	DHCP中继转发客户端
IP地址	192.168.32.80		vm1 192.168.32.1 vm2 192.168.33.1
网关	192.168.32.1		--

2. 实验步骤

(1). 配置master机器网卡
[root@master ~]# vim /etc/sysconfig/network-scripts/ifcfg-eth0

    DEVICE=eth0
    HWADDR=00:0C:29:63:EA:94
    TYPE=Ethernet
    UUID=70f2ac2f-2ed4-4f12-887c-f545bf45df8f
    ONBOOT=yes
    NM_CONTROLLED=yes
    BOOTPROTO=static
    IPADDR=192.168.32.80
    NETMASK=255.255.255.0
    GATEWAY=192.168.32.1

(2). 重启网卡
[root@master ~]# service network restart
正在关闭接口 eth0： [确定]
关闭环回接口： [确定]
弹出环回接口： [确定]
弹出界面 eth0： Determining if ip address 192.168.32.80 is already in use for device eth0...
[确定]
[root@master ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.32.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
169.254.0.0 0.0.0.0 255.255.0.0 U 1002 0 0 eth0
0.0.0.0 192.168.32.1 0.0.0.0 UG 0 0 0 eth0

(3). 修改配置文件

    # dhcpd.conf
    #
    # Sample configuration file for ISC dhcpd
    #

    # option definitions common to all supported networks...
    option domain-name "example.org";
    option domain-name-servers ns1.example.org, ns2.example.org;

    default-lease-time 600;
    max-lease-time 7200;


    # Use this to send dhcp log messages to a different log file (you also
    # have to hack syslog.conf to complete the redirection).
    log-facility local7;

      subnet 192.168.32.0 netmask 255.255.255.0 {
      range 192.168.32.20 192.168.32.200;
      option domain-name-servers 114.114.114.114,8.8.8.8;
      option routers 192.168.32.1;
      default-lease-time 600;
      max-lease-time 7200;
    }
    subnet 192.168.33.0 netmask 255.255.255.0 {
      range 192.168.33.30 192.168.33.200;
      option domain-name-servers 114.114.114.114,8.8.8.8;
      option routers 192.168.33.1;
      default-lease-time 600;
      max-lease-time 7200;
    }

    host passacaglia {
      hardware ethernet 0:0:c0:5d:bd:95;
      filename "vmunix.passacaglia";
      server-name "toccata.fugue.com";
    }

(4). 修改slave2中继器网卡配置文件eth0:

(5). 修改slave2的eth1网卡配置文件

(6). slave2开启路由转发

vim /etc/sysctl.conf

sysctl -p 生效

(7). 安装dhcrelay

[root@slave2 ~]# yum install -y dhcp

(8). 修改中继配置文件

[root@slave2 ~]# vim /etc/sysconfig/dhcrelay

    # Command line options here
    DHCRELAYARGS=""
    # DHCPv4 only
    INTERFACES="eth0 eth1"
    # DHCPv4 only
    DHCPSERVERS="192.168.32.80"

(9). 重启中继服务

[root@slave2 ~]# /etc/init.d/dhcrelay restart
正在启动 dhcrelay： [确定]

(10). slave1和slave3重启网卡（网卡配置文件别忘改成dhcp）

[root@slave1 ~]# service network restart
正在关闭接口 eth0： [确定]
正在关闭接口 eth1： [确定]
关闭环回接口： [确定]
弹出环回接口： [确定]
弹出界面 eth0：
正在决定 eth0 的 IP 信息...完成。
[root@slave1 ~]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:29:B1:18:8D
inet addr:192.168.32.20 Bcast:192.168.32.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:feb1:188d/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1755 errors:0 dropped:0 overruns:0 frame:0
TX packets:818 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:189969 (185.5 KiB) TX bytes:104084 (101.6 KiB)

---

[root@slave3 ~]# systemctl restart network
[root@slave3 ~]# ifconfig
ens33: flags=4163 mtu 1500
inet 192.168.33.30 netmask 255.255.255.0 broadcast 192.168.33.255
inet6 fe80::8fd:c838:d2f4:15ce prefixlen 64 scopeid 0x20
ether 00:0c:29:82:a8:c9 txqueuelen 1000 (Ethernet)
RX packets 239 bytes 25362 (24.7 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 227 bytes 27096 (26.4 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

---

(11). ping查看是否通信

[root@slave1 ~]# ping 192.168.33.30 -c 1
PING 192.168.33.30 (192.168.33.30) 56(84) bytes of data.
64 bytes from 192.168.33.30: icmp_seq=1 ttl=128 time=0.645 ms

--- 192.168.33.30 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.645/0.645/0.645/0.000 ms

---

[root@slave3 yum.repos.d]# ping 192.168.32.20 -c 1
PING 192.168.32.20 (192.168.32.20) 56(84) bytes of data.
64 bytes from 192.168.32.20: icmp_seq=1 ttl=63 time=0.645 ms

--- 192.168.32.20 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.645/0.645/0.645/0.000 ms

五. 小结

在中继dhcp配置的过程中可能存在的问题

    描述:
        dhcp中继分配完的主机只能ping通单向主机
    解决办法:
        route -n查看路由表，发现配置双网卡，nat模式的网关占用了dhcp分配的网关，导致所有的数据包通过nat模式的网关口出去。最后将nat模式的网卡网关删除，重启网卡即可恢复正常。