Router>enable
Router#conf t
Router(config)#host r1
R1(config)#int s2/1
R1(config-if)#ip add 12.1.1.1 255.255.255.0
R1(config-if)#no shut
R1(config-if)#exit
R1(config)#int f0/0
R1(config)#ip add 172.16.10.1 255.255.255.0
R1(config)#no shut

    Router>enable
Router#conf t
Router(config)#int s2/1
Router(config-if)#ip add 12.1.1.2 255.255.255.0
Router(config-if)#no shut
Router(config-if)#exit
Router(config)#int f0/0
Router(config-if)#ip add 172.16.20.1 255.255.255.0
Router(config-if)#no shut

   R1（config）#router rip
R1（config-route）#net 12.0.0.0
R1（config-route）#net 172.16.10.0

    R2（config）#router rip
R2（config-route）#net 12.0.0.0
R2（config-route）#net 172.16.20.0

  R1#ping 172.16.20.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.20.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/1)
R1#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
   D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
   N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
   E1 - OSPF external type 1, E2 - OSPF external type 2
   i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
  ia - IS-IS inter area, * - candidate default, U - per-user static route
  o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
     172.16.0.0/24 is subnetted, 1 subnets
C       172.16.10.0 is directly connected, FastEthernet0/0
     12.0.0.0/24 is subnetted, 1 subnets
C       12.1.1.0 is directly connected, Serial2/1
r2#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
  D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
  N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
  E1 - OSPF external type 1, E2 - OSPF external type 2
  i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
  ia - IS-IS inter area, * - candidate default, U - per-user static route
  o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
     172.16.0.0/24 is subnetted, 1 subnets
C       172.16.20.0 is directly connected, FastEthernet0/0
     12.0.0.0/24 is subnetted, 1 subnets
C       12.1.1.0 is directly connected, Serial2/1
r2#show ip pro
Routing Protocol is "rip"
  Sending updates every 30 seconds, next due in 1 seconds
  Invalid after 180 seconds, hold down 180, flushed after 240
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Redistributing: rip
  Default version control: send version 1, receive any version
    Interface           Send  Recv  Triggered RIP  Key-chain
    FastEthernet0/0       1     1 2                                  
    Serial2/1             1     1 2                                  
  Automatic network summarization is in effect
  Maximum path: 4
  Routing for Networks:
    12.0.0.0
    172.16.0.0
  Routing Information Sources:
    Gateway         Distance      Last Update
    12.1.1.1             120      00:00:24
  Distance: (default is 120)

  R1(config)#router rip
R1(config-router)#version 2
R2(config)#router rip
R2(config-router)#version 2
r1#show ip pro    //注意查看變化
Routing Protocol is "rip"
  Sending updates every 30 seconds, next due in 15 seconds
  Invalid after 180 seconds, hold down 180, flushed after 240
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Redistributing: rip
  Default version control: send version 2, receive version 2
    Interface           Send  Recv  Triggered RIP  Key-chain
    FastEthernet0/0       2     2                                    
    Serial2/1             2     2                                    
  Automatic network summarization is in effect
  Maximum path: 4
  Routing for Networks:
    12.0.0.0
    172.16.0.0
  Routing Information Sources:
    Gateway         Distance      Last Update
    12.1.1.2             120      00:00:02
  Distance: (default is 120)
r2#show ip pro
Routing Protocol is "rip"
  Sending updates every 30 seconds, next due in 10 seconds
  Invalid after 180 seconds, hold down 180, flushed after 240
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Redistributing: rip
  Default version control: send version 2, receive version 2
    Interface           Send  Recv  Triggered RIP  Key-chain
    FastEthernet0/0       2     2                                    
    Serial2/1             2     2                                    
  Automatic network summarization is in effect
  Maximum path: 4
  Routing for Networks:
    12.0.0.0
    172.16.0.0
  Routing Information Sources:
    Gateway         Distance      Last Update
    12.1.1.1             120      00:00:00
  Distance: (default is 120)

   r1#ping 172.16.20.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.20.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 56/114/196 ms
r2#ping 172.16.10.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.10.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 24/108/200 ms

    r1(config)#ip route 172.16.20.0 255.255.255.0 12.1.1.2
R2(config)#ip route 172.16.10.0 255.255.255.0 12.1.1.1
 
r1#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * -  candidate defa ult, U - per-user static route 
 o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
     172.16.0.0/24 is subnetted, 2 subnets
S       172.16.20.0 [1/0] via 12.1.1.2
C       172.16.10.0 is directly connected, FastEthernet0/0
     12.0.0.0/24 is subnetted, 1 subnets
C       12.1.1.0 is directly connected, Serial2/1

    R1#config t
R1(conf ig)#router rip
R1(conf ig- router)#net 12.0.0.0
R1(conf ig- router)#net 172.16.10.0
R1(config-router)#int s2/1
R1(config-if)#ip rip send version 2
R1(config-if)#int f0/0
R1(config-if)#ip rip send version 2

   R2#config t
R2(conf ig)#router rip
R2(conf ig- router)#net 12.0.0.0
R2(conf ig- router)#net 172.16.20.0
R2(config-router)#int s2/1
R2(config-if)#ip rip send version 2
R2(config-if)#int f0/0
R2(config-if)#ip rip send version 2

   R1#Ping 172.16.20.1 
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.20.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 32/109/208 ms
r1#show ip pro
Routing Protocol is "rip"
  Sending updates every 30 seconds, next due in 22 seconds
  Invalid after 180 seconds, hold down 180, flushed after 240
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Redistributing: rip
  Default version control: send version 1, receive any version
    Interface             Send  Recv  Triggered RIP  Key-chain
    FastEthernet0/0       2     1 2                                  
    Serial2/1             2     1 2                                  
  Automatic network summarization is in effect
  Maximum path: 4
  Routing for Networks:
    12.0.0.0
    172.16.0.0
  Routing Information Sources:
    Gateway         Distance      Last Update
    12.0.0.2             120      00:00:10
  Distance: (default is 120)

    R1(config)#int s2/1
R1(config-if)#ip add 172.16.30.1 255.255.255.0 secondary
R2(config)#int s2/1
R2(config-if)#ip add 172.16.30.2 255.255.255.0 secondary
R2#  show run int s2/1
Building configuration...
Current configuration : 134 bytes
!
interface Serial2/1
 ip address 172.16.30.2 255.255.255.0 secondary
 ip address 12.0.0.2 255.255.255.0
 serial restart-delay 0
end
R1#  show run int s2/1
Building configuration...
Current configuration : 134 bytes
!
interface Serial2/1
 ip address 172.16.30.1 255.255.255.0 secondary
 ip address 12.0.0.1 255.255.255.0
 serial restart-delay 0
end