cisco交换机作dhcp中继

有一次到一公司去面试，问到客户端DHCP的事,我只是简单的把原理说出来，后面试官要我写命令，因刚接触CISCO不久，把命令写得乱七八糟的，最后就把这个工作机会给弄丢了，今天在小凡上面以3725路由器模拟WINDOWS 2003作DHCP服务器，CISCO交换机作DHCP RELAY的一个DHCP网络环境，希望新手看到后，有所收获。

 

设备：四台3725路由器，SW4作DHCP SERVER，SW1,SW2,SW3作交换机。4台DHCP客户端，一台与DHCP SERVER

 

数据：SW4作如下DHCP 池

             pool vlan2 172.18.1.0 255.255.255.0 gateway 172.18.1.10

             pool vlan3 172.18.3.0 255.255.255.0 gateway 172.18.3.254

             pool vlan4 172.18.4.0 255.255.255.0 gateway 172.18.4.254

             pool vlan5 172.18.5.0 255.255.255.0 gateway 172.18.5.254

             f1/1 ip 172.18.1.11(模拟windows的IP地址)

             ip route 0.0.0.0 0.0.0.0 172.18.1.10（模拟windows的网关）

 

             SW1交换机划分VLAN 2,VLAN3,VLAN4,VLAN5

            VLAN2 IP 172.18.1.10

            VLAN3 IP 172.18.3.254

            VLAN4 IP 172.18.4.254

            VLAN5 IP 172.18.5.254

            F1/1 ,F1/4 属于 vlan2,并且f1/4接PC4 (设计目的为，同一 vlan里，应该不要用ip helper-address命令，就可以获取IP)

            F1/2属于 vlan3（设计目的为，不同VLAN里，应用ip helper-address命令，可以获取vlan 3的IP）

            f1/3 trunk 口（设计目的为，如果dhcp广播通过trunk后，各个vlan应用ip helper-address命令后，能不能获取各自的IP)

           

            SW2交换机

            f1/2 接sw1的f1/2

            f1/1 接pc1

           

            SW3交换机划分vlan4,vlan5

            f1/3 trunk口接sw1的f1/3

            f1/1 属于 vlan4 接pc2

            f1/2 属于 vlan5接pc3

具体拓朴图如下：

 

SW1,SW2,SW3,SW4的具体配置分别如下：

 

R1的具体配置：
R1#sh run
Building configuration...

Current configuration : 1461 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R1
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
ip cef
!
!
multilink bundle-name authenticated
!
interface FastEthernet1/0
!
interface FastEthernet1/1
 switchport access vlan 2 (把它放到vlan2里，vlan1一般作管理地址)
!
interface FastEthernet1/2
 switchport access vlan 3 (接下级交换机，如果下级交换机没有划分vlan，那么这个交换机的所有口都属于vlan3)
!
interface FastEthernet1/3
 switchport mode trunk (便于vlan4,vlan5通过trunk口与下级交换机SW3通信)
!
interface FastEthernet1/4
 switchport access vlan 2 (这个口接PC，验证同vlan里DHCP情况)
!
interface FastEthernet1/5
!
interface FastEthernet1/6
!
interface Vlan1
 no ip address
!
interface Vlan2
 ip address 172.18.1.10 255.255.255.0  （设个IP，意为着SW4在vlan2的网络里）
!
interface Vlan3
 ip address 172.18.3.254 255.255.255.0
 ip helper-address 172.18.1.11        （这里为SW4的IP，即服务器的IP地址）
!
interface Vlan4
 ip address 172.18.4.254 255.255.255.0
 ip helper-address 172.18.1.11
!
interface Vlan5
 ip address 172.18.5.254 255.255.255.0
 ip helper-address 172.18.1.11
!
!
ip http server
no ip http secure-server
!
!
control-plane
!
!
line con 0
line aux 0
line vty 0 4
 login
!
!
end

=============
R2的具体配置：
R2#sh run
Building configuration...

Current configuration : 1040 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R2
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
ip cef
!
!
!
!
multilink bundle-name authenticated
!
interface FastEthernet1/0
!
interface FastEthernet1/1
!
interface FastEthernet1/2
!
interface FastEthernet1/3
!
interface FastEthernet1/4
!
interface FastEthernet1/5
!
interface Vlan1                           （这个交换机没有什么配置的，当HUB用）
 no ip address
!
!
ip http server
no ip http secure-server
!
!
control-plane
!
!
line con 0
line aux 0
line vty 0 4
 login
!
!
end

=========
R3的具体配置：
R3#sh run
Building configuration...

Current configuration : 1243 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R3
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
ip cef
!
!
!
!
multilink bundle-name authenticated
!
interface FastEthernet1/0
!
interface FastEthernet1/1
 switchport access vlan 4
!
interface FastEthernet1/2
 switchport access vlan 5
!
interface FastEthernet1/3
 switchport mode trunk           （本交换机的vlan4,vlan5数据通过这个口上连至SW）
!
interface FastEthernet1/4
!
interface FastEthernet1/5
!
interface FastEthernet1/6
!
interface FastEthernet1/7
!
interface Vlan1
 no ip address
!
interface Vlan4
 no ip address
!
interface Vlan5
 no ip address
!
!
ip http server
no ip http secure-server
!
!
control-plane
!
!
line con 0
line aux 0
line vty 0 4
 login
!
!
end

==============
R4的具体配置：
R4#sh run
Building configuration...

Current configuration : 1774 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R4
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
ip cef
!
!
no ip dhcp use vrf connected
!
ip dhcp pool vlan2                            （cisco作dhcp服务器的命令）
   network 172.18.1.0 255.255.255.0
   default-router 172.18.1.10
   dns-server 172.18.1.110
   netbios-name-server 172.18.1.110
!
ip dhcp pool vlan3
   network 172.18.3.0 255.255.255.0
   default-router 172.18.3.254
   dns-server 172.18.1.110
   netbios-name-server 172.18.1.110
!
ip dhcp pool vlan4
   network 172.18.4.0 255.255.255.0
   default-router 172.18.4.254
   netbios-name-server 172.18.1.110
   dns-server 172.18.1.110
!
ip dhcp pool vlan5
   network 172.18.5.0 255.255.255.0
   dns-server 172.18.1.110
   netbios-name-server 172.18.1.110
   default-router 172.18.5.254
!
!
multilink bundle-name authenticated
!
interface FastEthernet1/0
!
interface FastEthernet1/1
 no switchport
 ip address 172.18.1.11 255.255.255.0
!
interface FastEthernet1/2
!
interface FastEthernet1/3
!
interface FastEthernet1/4
!
interface FastEthernet1/5
!
interface FastEthernet1/6
!
interface FastEthernet1/7
!
interface Vlan1
 no ip address
!
ip route 0.0.0.0 0.0.0.0 172.18.1.10    （模拟windwos服务器的网关）
!
ip http server
no ip http secure-server
!
!
control-plane
!
!
line con 0
line aux 0
line vty 0 4
 login
!
!
end

R4#

 

要注意的地方：

ip helper-address 的地址一定是dhcp server服务器的ip地址，不是dhcp server服务器所在网络的网关。