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)

[[email protected] ~]# ifconfig 
ens33: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.94.11  netmask 255.255.255.0  broadcast 192.168.94.255
        inet6 fe80::20c:29ff:fe54:3372  prefixlen 64  scopeid 0x20<link>
        ether 00:0c:29:54:33:72  txqueuelen 1000  (Ethernet)
        RX packets 9733  bytes 11834218 (11.2 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 3320  bytes 436871 (426.6 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

ens37: flags=4163<UP,MULTICAST>  mtu 1500
        inet 192.168.29.29  netmask 255.255.255.0  broadcast 192.168.29.255
        inet6 fe80::20c:29ff:fe54:337c  prefixlen 64  scopeid 0x20<link>
        ether 00:0c:29:54:33:7c  txqueuelen 1000  (Ethernet)
        RX packets 122  bytes 13196 (12.8 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 82  bytes 12760 (12.4 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 9  bytes 1149 (1.1 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 9  bytes 1149 (1.1 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

修改DHCP服务配置文件

[[email protected] ~]# yum install dhcp -y
[[email protected] ~]# 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

[[email protected] ~]# systemctl start dhcpd
[[email protected] ~]# 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 2018-08-21 13:58:25 CST; 1min 31s ago
     Docs: man:dhcpd(8)
           man:dhcpd.conf(5)
 Main PID: 3421 (dhcpd)
   Status: "Dispatching packets..."
   CGroup: /system.slice/dhcpd.service
           └─3421 /usr/sbin/dhcpd -f -cf /etc/dhcp/dhcpd.conf -user dhcpd -group dhcpd --n...

8月 21 13:58:25 DaMoWang dhcpd[3421]: All rights reserved.
8月 21 13:58:25 DaMoWang dhcpd[3421]: For info,please visit https://www.isc.org/softw...cp/
8月 21 13:58:25 DaMoWang dhcpd[3421]: Not searching LDAP since ldap-server,ldap-port ...ile
8月 21 13:58:25 DaMoWang dhcpd[3421]: Wrote 0 leases to leases file.
8月 21 13:58:25 DaMoWang dhcpd[3421]: Listening on LPF/ens37/00:0c:29:54:33:7c/192.168.../24
8月 21 13:58:25 DaMoWang dhcpd[3421]: Sending on   LPF/ens37/00:0c:29:54:33:7c/192.168.../24
8月 21 13:58:25 DaMoWang dhcpd[3421]: Listening on LPF/ens33/00:0c:29:54:33:72/192.168.../24
8月 21 13:58:25 DaMoWang dhcpd[3421]: Sending on   LPF/ens33/00:0c:29:54:33:72/192.168.../24
8月 21 13:58:25 DaMoWang dhcpd[3421]: Sending on   Socket/fallback/fallback-net
8月 21 13:58:25 DaMoWang systemd[1]: 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
[[email protected] ~]# vim /etc/sysctl.conf
# 添加 net.ipv4.ip_forward=1
[[email protected] ~]# sysctl -p
net.ipv4.ip_forward = 1
[[email protected] ~]# vim /etc/sysconfig/dhcrelay
INTERFACES=ens33                         # DHCP服务器网卡名称                                                   
DHCPSERVERS="192.168.94.11"        #  DHCP服务器IP
[[email protected] ~]# dhcrelay 192.168.94.11　　# 启动DHCP中继代理服务
Dropped all unnecessary capabilities.
Internet Systems Consortium DHCP Relay Agent 4.2.5
Copyright 2004-2013 Internet Systems Consortium.
All rights reserved.
For info,please visit https://www.isc.org/software/dhcp/
Listening on LPF/ens37/00:0c:29:54:33:7c
Sending on   LPF/ens37/00:0c:29:54:33:7c
Listening on LPF/ens33/00:0c:29:54:33:72
Sending on   LPF/ens33/00:0c:29:54:33:72
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