CentOS 7 配置DHCP中继代理服务

DHCP服务器只作用于局域网同一网段内，客户端是通过广播消息来获得DHCP服务器响应后才能得到IP地址的，但广播消息不能跨越子网，那么如何让客户端获取到DHCP服务器提供的IP地址呢？这就是DHCP中继服务器的功能了

添加一块网卡

192.168.94.11 ens33(NAT)  　　192.168.29.29(VMnet2)

[root@DaMoWang ~]# ifconfig
ens33: flags=<UP,BROADCAST,RUNNING,MULTICAST>  mtu
        inet 192.168.94.11  netmask 255.255.255.0  broadcast 192.168.94.255
        inet6 fe80::20c:29ff:fe54:  prefixlen   scopeid 0x20<link>
        ether :0c::::  txqueuelen   (Ethernet)
        RX packets   bytes  (11.2 MiB)
        RX errors   dropped   overruns   frame
        TX packets   bytes  (426.6 KiB)
        TX errors   dropped  overruns   carrier   collisions 

ens37: flags=<UP,BROADCAST,RUNNING,MULTICAST>  mtu
        inet 192.168.29.29  netmask 255.255.255.0  broadcast 192.168.29.255
        inet6 fe80::20c:29ff:fe54:337c  prefixlen   scopeid 0x20<link>
        ether :0c::::7c  txqueuelen   (Ethernet)
        RX packets   bytes  (12.8 KiB)
        RX errors   dropped   overruns   frame
        TX packets   bytes  (12.4 KiB)
        TX errors   dropped  overruns   carrier   collisions 

lo: flags=<UP,LOOPBACK,RUNNING>  mtu
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::  prefixlen   scopeid 0x10<host>
        loop  txqueuelen   (Local Loopback)
        RX packets   bytes  (1.1 KiB)
        RX errors   dropped   overruns   frame
        TX packets   bytes  (1.1 KiB)
        TX errors   dropped  overruns   carrier   collisions 

修改DHCP服务配置文件

[root@DaMoWang ~]# yum install dhcp -y
[root@DaMoWang ~]# vim /etc/dhcp/dhcpd.conf

option  domain-name-servers  202.106.0.20,8.8.8.8;

subnet  192.168.94.0 netmask 255.255.255.0 {
        range  192.168.94.100 192.168.94.254;
        option routers 192.168.94.11;

}
subnet 192.168.29.0 netmask 255.255.255.0 {
            range 192.168.29.100  192.168.29.254;
            option routers 192.168.29.29;

}

启动DHCP服务，并检查状态

[root@DaMoWang ~]# systemctl start dhcpd
[root@DaMoWang ~]# systemctl status dhcpd
● dhcpd.service - DHCPv4 Server Daemon
   Loaded: loaded (/usr/lib/systemd/system/dhcpd.service; disabled; vendor preset: disabled)
   Active: active (running) since 二 -- :: CST; 1min 31s ago
     Docs: man:dhcpd()
           man:dhcpd.conf()
 Main PID:  (dhcpd)
   Status: "Dispatching packets..."
   CGroup: /system.slice/dhcpd.service
           └─ /usr/sbin/dhcpd -f -cf /etc/dhcp/dhcpd.conf -user dhcpd -group dhcpd --n...

8月  :: DaMoWang dhcpd[]: All rights reserved.
8月  :: DaMoWang dhcpd[]: For info, please visit https://www.isc.org/softw...cp/
8月  :: DaMoWang dhcpd[]: Not searching LDAP since ldap-server, ldap-port ...ile
8月  :: DaMoWang dhcpd[]: Wrote  leases to leases file.
8月  :: DaMoWang dhcpd[]: Listening on LPF/ens37/:0c::::7c/192.168.../
8月  :: DaMoWang dhcpd[]: Sending on   LPF/ens37/:0c::::7c/192.168.../
8月  :: DaMoWang dhcpd[]: Listening on LPF/ens33/:0c::::/192.168.../
8月  :: DaMoWang dhcpd[]: Sending on   LPF/ens33/:0c::::/192.168.../
8月  :: DaMoWang dhcpd[]: Sending on   Socket/fallback/fallback-net
8月  :: DaMoWang systemd[]: Started DHCPv4 Server Daemon.
Hint: Some lines were ellipsized, use -l to show in full.

配置DHCP中继服务器

# 开启路由转发功能
[root@DaMoWang ~]# vim /etc/sysctl.conf
# 添加 net.ipv4.ip_forward=
[root@DaMoWang ~]# sysctl -p
net.ipv4.ip_forward =
[root@DaMoWang ~]# vim /etc/sysconfig/dhcrelay
INTERFACES=ens33                         # DHCP服务器网卡名称
DHCPSERVERS="192.168.94.11"        #  DHCP服务器IP
[root@DaMoWang ~]# dhcrelay 192.168.94.11　　# 启动DHCP中继代理服务
Dropped all unnecessary capabilities.
Internet Systems Consortium DHCP Relay Agent 4.2.
Copyright - Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/
Listening on LPF/ens37/:0c::::7c
Sending on   LPF/ens37/:0c::::7c
Listening on LPF/ens33/:0c::::
Sending on   LPF/ens33/:0c::::
Sending on   Socket/fallback

用另一台虚拟机测试

网卡先用VMnet2

网段 IP 掩码 DNS都和DHCP服务器分配的一致

NAT

分配的IP等信息也一致

DHCP中继服务配置完成