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 192.168.13.3/24
  Broadcast address is 255.255.255.255
  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).

Links:

https://forum.networklessons.com/t/troubleshooting-eigrp-route-advertisement/1188/10?u=lagapides