Troubleshooting EIGRP Route Advertisement

Hello Samir

Actually, that’s quite interesting. At first I thought it would be an issue with how the tunnel interface interprets split horizon commands, so I went into the lab to check it out.

It turns out that it has nothing to do with tunnel interfaces. I found that the output of the show ip interface command informs you about whether or not split horizon is enabled or disabled only for the RIP protocol. So if you issue the following command on your interface:

no ip split-horizon eigrp 1

split horizon will be disabled for EIGRP. This will not affect the output of the show ip interface command. It still states that split horizon is enabled. However, if you issue this command:

no ip split-horizon

which disables split horizon for the RIP protocol, then the output of the show ip interface command will show that split horizon is disabled.

This is really strange, and I believe Cisco should have resolved this, because it can be confusing. I searched command reference documentation such as that in the following link, but the only thing they say for the split horizon info is that it “Shows whether split horizon is enabled.”

So to answer your question, is there any way of determining the state of split horizon for EIGRP without looking at the running configuration? After doing a bit more experimentation in the lab, I found the following:

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 <none>
  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:


With this command, you can see that it states that split horizon is indeed disabled, and this is EIGRP-specific, so it is displaying the correct information.

I hope this has been helpful!