EIGRP split horizon verification

Both EIGRP and RIP are dynamic routing protocols that use the Split-horizon rule to avoid routing loops. However, verification of the configuration of split horizon on Cisco IOS routers is somewhat different for each.

Using the show ip interface command will show whether or not split-horizon is enabled on a particular interface, but only for the RIP protocol. For example:

R3#show ip interface gigabitethernet 0/1 GigabitEthernet0/1 is up, line protocol is up Internet address is Broadcast address is Address determined by configuration file MTU is 1500 bytes ! ! > -- Output Omitted -- < ! Split horizon is enabled ! ! > -- Output Omitted -- < ! R3#

If split horizon is disabled for EIGRP on this particular interface, it will still indicate that split horizon is enabled. Only when it is disabled for RIP will this indicator change.

To determine the current state of split horizon for EIGRP, use the show ip eigrp interfaces detail command like so:

R1#show ip eigrp interfaces detail gigabitEthernet 0/1 EIGRP-IPv4 Interfaces for AS(1) Xmit Queue PeerQ Mean Pacing Time Multicast Pending Interface Peers Un/Reliable Un/Reliable SRTT Un/Reliable Flow Timer Routes Gi0/1 1 0/0 0/0 1 0/0 50 0 Hello-interval is 5, Hold-time is 15 Split-horizon is disabled Next xmit serial Packetized sent/expedited: 42/0 Hello's sent/expedited: 286/2 Un/reliable mcasts: 0/41 Un/reliable ucasts: 44/3 Mcast exceptions: 0 CR packets: 0 ACKs suppressed: 0 Retransmissions sent: 1 Out-of-sequence rcvd: 0 Topology-ids on interface - 0 Authentication mode is not set Topologies advertised on this interface: base Topologies not advertised on this interface: R1#

Notice that in this output, it states that split-horizon is disabled. This refers only to the split horizon configured using EIGRP.

This has been confirmed using Cisco's CML VIOS-ADVENTERPRISEK9-M), Version 15.9(3)M4, RELEASE SOFTWARE (fc3).