RIP Split Horizon

Split Horizon

RIP functions by periodically flooding the entire routing table out to the network, it generates a lot of traffic. The split horizon and poison reverse techniques can help to reduce the large amount of network traffic .Never tell someone what they told you .

R1#sh run | s rip
router rip
version 2
passive-interface FastEthernet0/0
network 1.0.0.0
network 10.0.0.0
neighbor 10.1.12.3
neighbor 10.1.12.2
no auto-summary


R2#sh run | s rip
router rip
version 2
passive-interface FastEthernet0/0
network 2.0.0.0
network 10.0.0.0
neighbor 10.1.12.1
no auto-summary


Split Horizon Rule is enable in RIP by default

R3#sh run | s rip
router rip
 version 2
 passive-interface FastEthernet0/0
 network 3.0.0.0
 network 10.0.0.0
 neighbor 10.1.12.1
 no auto-summary

R3(config)#int f 0/0
R3(config-if)#shut
R3(config-if)#no shut

R3#sh ip int f 0/0
FastEthernet0/0 is up, line protocol is up
  Internet address is 10.1.12.3/24
  Broadcast address is 255.255.255.255
  Address determined by setup command
  MTU is 1500 bytes
  Helper address is not set
  Directed broadcast forwarding is disabled
  Multicast reserved groups joined: 224.0.0.9
  Outgoing access list is not set
  Inbound  access list is not set
  Proxy ARP is enabled
  Local Proxy ARP is disabled
  Security level is default
  Split horizon is enabled

R1#sh ip route rip
     2.0.0.0/24 is subnetted, 1 subnets
R       2.2.2.0 [120/1] via 10.1.12.2, 00:00:13, FastEthernet0/0
     3.0.0.0/24 is subnetted, 1 subnets
R       3.3.3.0 [120/1] via 10.1.12.3, 00:00:14, FastEthernet0/0

R3#sh ip route rip

     1.0.0.0/24 is subnetted, 1 subnets
R       1.1.1.0 [120/1] via 10.1.12.1, 00:00:05, FastEthernet0/0

After disable Split Horizon in RIP

R3(config)#int f 0/0
R3(config-if)#no ip split-horizon

R3(config-if)#do sh ip int f 0/0
FastEthernet0/0 is up, line protocol is up
Internet address is 10.1.12.3/24
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500 bytes
Helper address is not set
Directed broadcast forwarding is disabled
Multicast reserved groups joined: 224.0.0.9
Outgoing access list is not set
Inbound access list is not set
Proxy ARP is enabled
Local Proxy ARP is disabled
Security level is default
Split horizon is disabled

R3(config-if)#do sh ip route rip
     1.0.0.0/24 is subnetted, 1 subnets
R       1.1.1.0 [120/1] via 10.1.12.1, 00:00:18, FastEthernet0/0
     2.0.0.0/24 is subnetted, 1 subnets

R       2.2.2.0 [120/2] via 10.1.12.2, 00:00:18, FastEthernet0/0