1-PC1有默认网关/Normal-ARP（正常ARP）

R2(config)#int f0/0
R2(config-if)#no shutdown
R2(config-if)#ip add 12.1.1.2 255.255.255.0
R2(config-if)#int f0/1
R2(config-if)#no shutdown
R2(config-if)#ip add 23.1.1.2 255.255.255.0

R3(config)#int f0/0
R3(config-if)#no shutdown
R3(config-if)#ip add 23.1.1.3 255.255.255.0
R3(config-if)#int lo1
R3(config-if)#ip add
R3(config-if)#ip add 3.3.3.3 255.255.255.0

重点部署：
PC1(config)#ip default-gateway 12.1.1.2
R2(config)#ip route 0.0.0.0 0.0.0.0 23.1.1.3
R3(config)#ip route 12.1.1.0 255.255.255.0 f0/0

3、抓包验证：
（1）查看R2—>f0/0的MAC地址、PC—>f0/0的MAC地址等
PC1#show arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 12.1.1.2 - c001.1858.0000 ARPA FastEthernet0/0

PC1#show int f0/0
FastEthernet0/0 is up, line protocol is up
Hardware is Gt96k FE, address is c001.1858.0000 (bia c001.1858.0000)

R2#show int f0/0
FastEthernet0/0 is up, line protocol is up
Hardware is Gt96k FE, address is c002.3430.0000 (bia c002.3430.0000)

清除ARP：
方法：先把PC1接口shutdown—>no shutdown—>clear arp-cache

R2开启Debug功能：
R2#debug arp
ARP packet debugging is on

（2）抓包结果：
R2#
Mar 1 00:28:34.899: IP ARP: rcvd req src 12.1.1.1 c001.1858.0000, dst 12.1.1.2 FastEthernet0/0
Mar 1 00:28:34.899: IP ARP: sent rep src 12.1.1.2 c002.3430.0000,
dst 12.1.1.1 c001.1858.0000 FastEthernet0/0
新版抓包，抓到的还是3.3.3.3的地址。
（3）看到的地址永远是R2的f0/0的MAC地址

1-PC1有默认网关/Normal-ARP（正常ARP）

原文：http://blog.51cto.com/13856092/2137350