Split Horizon menjadi masalah pada jaringan frame relay khususnya frame relay hub and spoke yang menggunakan sub-interface, karena pada serial physical interface ip split horizon defaultnya adalah disabled sementara pada sub-interface enabled.
R2(config)#interface s1/0
R2(config-if)#encapsulation frame-relay
R2(config-if)#ip add 10.10.10.2 255.255.255.0
R2(config-if)#frame-relay map ip 10.10.10.1 201 broadcast
R2(config-if)#frame-relay map ip 10.10.10.3 201
R2(config-if)#no shut
R2(config-if)#interface lo0
R2(config-if)#ip add 2.2.2.2 255.255.255.255
R2(config-if)#router rip
R2(config-router)#v 2
R2(config-router)#network 0.0.0.0
R2(config-router)#no auto-summary
R3(config)#interface s1/0
R3(config-if)#encapsulation frame-relay
R3(config-if)#ip add 10.10.10.3 255.255.255.0
R3(config-if)#frame-relay map ip 10.10.10.1 301 broadcast
R3(config-if)#frame-relay map ip 10.10.10.2 301
R3(config-if)#no shut
R3(config-if)#interface lo0
R3(config-if)#ip add 3.3.3.3 255.255.255.255
R3(config-if)#router rip
R3(config-router)#v 2
R3(config-router)#network 0.0.0.0
R3(config-router)#no auto-summary
R1(config)#interface s1/0
R1(config-if)#encapsulation frame-relay
R1(config-if)#no shut
R1(config)#interface s1/0.1 multipoint
R1(config-subif)#ip add 10.10.10.1 255.255.255.0
R1(config-subif)#frame-relay map ip 10.10.10.2 102 broadcast
R1(config-subif)#frame-relay map ip 10.10.10.3 103 broadcast
R1(config)#router rip
R1(config-router)#v 2
R1(config-router)#network 0.0.0.0
R1(config-router)#no auto-summary
pada routing tabel R2 hanya ada RIP dari loopback R1
R2#show ip route
R 1.0.0.0/8 [120/1] via 10.10.10.1, 00:00:25, Serial1/0
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
10.0.0.0/24 is subnetted, 1 subnets
C 10.10.10.0 is directly connected, Serial1/0
informasi routing di R1 lengkap, namun R1 tidak akan mengirimkan update dari R2 ke R3 melalui s1/0.1 maupun sebaliknya.
R1#show ip route
1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 1.1.1.1/32 is directly connected, Loopback0
R 1.0.0.0/8 [120/1] via 10.10.10.3, 00:00:23, Serial1/0.1
[120/1] via 10.10.10.2, 00:00:07, Serial1/0.1
R 2.0.0.0/8 [120/1] via 10.10.10.2, 00:00:07, Serial1/0.1
R 3.0.0.0/8 [120/1] via 10.10.10.3, 00:00:23, Serial1/0.1
10.0.0.0/24 is subnetted, 1 subnets
C 10.10.10.0 is directly connected, Serial1/0.1
R1#show ip interface s1/0.1
Serial1/0.1 is up, line protocol is up
Internet address is 10.10.10.1/24
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
ICMP redirects are always sent
ICMP unreachables are always sent
ICMP mask replies are never sent
IP fast switching is enabled
IP fast switching on the same interface is enabled
IP Flow switching is disabled
IP CEF switching is enabled
IP CEF Fast switching turbo vector
IP multicast fast switching is enabled
--More--
R1(config)#interface s1/0.1cek ladi di routing tabel R2 dan R3. Pastikan bisa ping ke loopback masing-masing.
R1(config-subif)#no ip split-horizon
R2#show ip route
1.0.0.0/32 is subnetted, 1 subnets
R 1.1.1.1 [120/1] via 10.10.10.1, 00:00:27, Serial1/0
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
R 3.3.3.3 [120/2] via 10.10.10.3, 00:00:27, Serial1/0
10.0.0.0/24 is subnetted, 1 subnets
C 10.10.10.0 is directly connected, Serial1/0
R2#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/24/44 ms