DHCP

用于终端设备自动获取IP地址、子网掩码、网关地址、DNS、租约时间等信息。
在cisco设备上默认IP地址租约时间是1天，终端设备在到期之前要续约，不然到期就会被收回。
终端设备需要提交Username、MAC地址、Client-ID这几种中的一个，来获取地址信息。
DHCP服务收到用户信息，会从IP地址池中选一个地址发给终端设备。

DHCP的过程

终端设备使用广播地址发起DHCP请求
DHCP服务器收到请求后用广播回复将要分配的地址信息
终端设备收到后确定地址信息
DHCP服务器收到确认后，正式回复地址信息发放信息

DHCP配置

ip dhcp excluded-address 192.168.1.1 192.168.1.99
# 这个范围内的IP地址不分配
ip dhcp excluded-address 192.168.1.201 192.168.1.254
ip dhcp pool cisco
 network 192.168.1.0 255.255.255.0
 default-router 192.168.1.6 
 dns-server 36.36.36.3 
 R6#sh ip dhcp binding 
Bindings from all pools not associated with VRF:
IP address          Client-ID/	 	    Lease expiration        Type
		    Hardware address/
		    User name
192.168.1.100       0063.6973.636f.2d61.    Dec 26 1990 11:20 PM    Automatic
                    6162.622e.6363.3030.
                    2e30.3430.302d.4574.
                    302f.30
192.168.1.101       0063.6973.636f.2d61.    Dec 26 1990 11:26 PM    Automatic
                    6162.622e.6363.3030.
                    2e30.3530.302d.4574.
                    302f.30

客户端获取IP地址

int e0/0
 ip add dhcp
 no sh

DHCP静态分配IP地址

dhcp服务器在知道对方的Client-ID、MAC地址或Username的情况下，可以指定分配的IP地址

首先获取Clinet-ID

清空现有的DHCP绑定池

clear ip dhcp bind *

进行如下配置

ip dhcp pool R4
 host 192.168.1.4 255.255.255.0
 client-identifier 0063.6973.636f.2d61.6162.622e.6363.3030.2e30.3430.302d.4574.302f.30
 default-router 192.168.1.6 
 dns-server 36.36.36.3 
ip dhcp pool R5
 host 192.168.1.5 255.255.255.0
 client-identifier 0063.6973.636f.2d61.6162.622e.6363.3030.2e30.3530.302d.4574.302f.30
 default-router 192.168.1.6 
 dns-server 36.36.36.3

最后要记得重启客户端的网卡

DHCP中继

为了让多个局域网可以集中管理，集中分配IP地址，有时候只会设置一台DHCP服务器，所有的设备都从这个设备上获取IP

实验拓扑

实验需求

R4和R5模拟终端设备，R1,R2,R3运行ospf，R2是dhcp给终端设备分配IP地址

R1
interface Ethernet0/0
 ip address 192.168.14.1 255.255.255.0
 ip helper-address 192.168.12.2
 ip ospf 1 area 0

interface Ethernet0/1
 ip address 192.168.12.1 255.255.255.0
 ip ospf 1 area 0
==============================
R2
ip dhcp pool 14
 network 192.168.14.0 255.255.255.0
 default-router 192.168.14.1 

ip dhcp pool 35
 network 192.168.35.0 255.255.255.0
 default-router 192.168.35.3 

interface Loopback0
 ip address 2.2.2.2 255.255.255.0
 ip ospf 1 area 0

interface Ethernet0/0
 ip address 192.168.12.2 255.255.255.0
 ip ospf 1 area 0

interface Ethernet0/1
 ip address 192.168.23.2 255.255.255.0
 ip ospf 1 area 0
==============================
R3
interface Ethernet0/0
 ip address 192.168.23.3 255.255.255.0
 ip ospf 1 area 0

interface Ethernet0/1
 ip address 192.168.35.3 255.255.255.0
 ip helper-address 2.2.2.2
 ip ospf 1 area 0
==============================
R4
interface Ethernet0/0
 ip address dhcp
==============================
R5
interface Ethernet0/0
 ip address dhcp