代理ARP（Proxy ARP）实验

1、测试R2 ping R3,观察ARP表。

配置命令：

R2#configure terminal
R2(config)#no ip routing     //关闭路由
R2(config)#interface fastEthernet 0/0
R2(config-if)#ip address 12.12.12.2 255.255.255.0
R2(config-if)#no shutdown
R2(config-if)#exit
R2(config)#ip default-gateway 12.12.12.1
---------------------------------------------------
R3#configure terminal
R3(config)#no ip routing     //关闭路由
R3(config)#interface fastEthernet 0/0
R3(config-if)#ip address 13.13.13.3 255.255.255.0
R3(config-if)#no shutdown
R3(config-if)#exit
R3(config)#ip default-gateway 13.13.13.1
---------------------------------------------------
R1#configure terminal
R1(config)#int fastEthernet 0/0
R1(config-if)#ip address 12.12.12.1 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#int f 1/0
R1(config-if)#ip address 13.13.13.1 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#end
---------------------------------------------------
//查看静态路由表
R1#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGPD - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2E1 - OSPF external type 1, E2 - OSPF external type 2i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2ia - IS-IS inter area, * - candidate default, U - per-user static routeo - ODR, P - periodic downloaded static routeGateway of last resort is not set12.0.0.0/24 is subnetted, 1 subnets
C       12.12.12.0 is directly connected, FastEthernet0/013.0.0.0/24 is subnetted, 1 subnets
C       13.13.13.0 is directly connected, FastEthernet1/0
---------------------------------------------------
R1#ping 12.12.12.2       //测试连通性
..!!!
Success rate is 60 percent (3/5), round-trip min/avg/max = 12/18/28 ms
R1#ping 13.13.13.3      //测试连通性
..!!!
Success rate is 60 percent (3/5), round-trip min/avg/max = 16/21/2
---------------------------------------------------
R2#ping 13.13.13.3Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 13.13.13.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 24/35/48 ms
R2#show arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  12.12.12.1             11   cc01.331c.0000  ARPA   FastEthernet0/0
Internet  12.12.12.2              -   cc02.37bc.0000  ARPA   FastEthernet0/0

结果&过程：

ping通，去往不同网段，送往网关，R1接到之后，查询路由表，13.13.13.0网段是直链路由条目，送往f1/0，这时R2的ARP表条目只有12网段的.1和.2的Mac

2、切断R1、R3之间的链路（R1的f1/0 shutdown)，并删掉R1、R3的网关（no),测试R2 ping R3,观察ARP表。

配置命令：

R2(config)#no ip default-gateway 12.12.12.1
R3(config)#no ip default-gateway 13.13.13.1
R1(config)#int fastEthernet 1/0
R1(config-if)#shutdown
---------------------------------------------
R2#ping 13.13.13.1      //ping 网关Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 13.13.13.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
R2#
R2#ping 13.13.13.3Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 13.13.13.3, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
R2#show arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  13.13.13.1              0   Incomplete      ARPA
Internet  12.12.12.1             17   cc01.331c.0000  ARPA   FastEthernet0/0
Internet  13.13.13.3              0   Incomplete      ARPA
Internet  12.12.12.2              -   cc02.37bc.0000  ARPA   FastEthernet0/0

结果&过程：

肯定是不通的，但是这时R2的ARP表条目，有三条，13.3的条目Mac地址显示不完整(Incomplete )
这时肯定是因为R2没有网关，不同网段，没法送到网关，只能通过ARP解析，代理ARP把去往13.3封装成f0/0接口，这个时候R1查路由表，往f1/0出去但是接口关闭了

3、把R1、R3之间的链路接上，测试R2 ping R3,观察ARP表。

配置命令：

R1(config)#int fastEthernet 1/0
R1(config-if)#no shutdown
-------------------------------------------------
R2#ping 13.13.13.3Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 13.13.13.3, timeout is 2 seconds:
..!!!
Success rate is 60 percent (3/5), round-trip min/avg/max = 32/34/40 ms
R2#show arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  12.12.12.1             22   cc01.331c.0000  ARPA   FastEthernet0/0
Internet  13.13.13.3              0   cc01.331c.0000  ARPA   FastEthernet0/0
Internet  12.12.12.2              -   cc02.37bc.0000  ARPA   FastEthernet0/0

结果&过程：

可以通，R2的ARP表条目，13.3的Mac地址是R1 f0/0 的Mac地址，这就是代理ARP协议

4、关闭R1 f0/0的代理ARP功能(no ip proxy-arp)，测试R2 ping R3,观察ARP表。

配置命令：

R1(config)#interface f0/0
R1(config-if)#no ip proxy-arp
------------------------------------------
//注意做实验过程中得清空arp表，保证实验的精准性
R2#clear arp
R2#ping 13.13.13.3Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 13.13.13.3, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
R2#show arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  12.12.12.2              -   cc02.37bc.0000  ARPA   FastEthernet0/0
------------------------------------------
R2#ping 12.12.12.1     //ping网关Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 12.12.12.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/220/1024 ms
R2#show arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  12.12.12.1              0   cc01.331c.0000  ARPA   FastEthernet0/0
Internet  12.12.12.2              -   cc02.37bc.0000  ARPA   FastEthernet0/0

结果&过程：

不通，R2的ARP条目只有二条，一条.2，一条.3不完整，不完整意味着无法封装；
要跨网段访问，没有网关，只能发送ARP解析，R1的f0/0关闭了代理ARP协议，结果没有人给回应，就无法获得Mac，丢包
但是ping 网关是正常的。

实验注意事项：

//注意做实验过程中得清空arp表，保证实验的精准性
R2#clear arp

查看arp代理是否开启的方法
1、show runn可以看到配置。

2、show interface可以看到端口的状态。

3、show ip interface fa 0/0 可以看到 proxy-arp的状态。

如何关闭接口代理ARP的功能
no ip proxy-arp