In the last article about EIGRP, I’ll go over some of the show and debug commands relevant to the operation of EIGRP.

Show the established neighbours:

r0#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H   Address                 Interface   Hold Uptime   SRTT   RTO  Q  Seq Type
                                        (sec)         (ms)       Cnt Num
1   192.168.1.136           Et0           13 00:00:29  404  2424  0  18
0   192.168.1.93            Et0           13 00:00:29   12   200  0  26

Watch the uptime and sequence numbers… Low uptime and increasing sequence numbers mean flapping. If there is a problem establishing an adjacency, you’ll see the process “waiting for init ack” or something similar:

r0#show ip eigrp neighbors detail
IP-EIGRP neighbors for process 1
H   Address                 Interface   Hold Uptime   SRTT   RTO  Q  Seq Type
                                        (sec)         (ms)       Cnt Num
0   192.168.1.136           Et0           14 00:00:00    1  2000  1  0
   Last startup serial 2
   Version 12.2/1.2, Retrans: 0, Retries: 0, Waiting for Init, Waiting for Init Ack, reinit for 576 msec

To debug neighbor adjacency problems, debug eigrp packets hello:

r1#debug eigrp packets hello
EIGRP Packets debugging is on
    (HELLO)
11:39:21: EIGRP: Received HELLO on Serial0.101 nbr 172.18.0.2
11:39:21:   AS 1, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0
11:39:21: EIGRP: Sending HELLO on Ethernet0
11:39:21:   AS 1, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0
11:39:22: EIGRP: Received HELLO on Ethernet0 nbr 192.168.1.93
11:39:22:   AS 1, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0
11:39:24: EIGRP: Received HELLO on Ethernet0 nbr 192.168.1.134
11:39:24:   AS 1, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/1
11:39:24: EIGRP: Sending HELLO on Serial0.101
11:39:24:   AS 1, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0
11:39:26: EIGRP: Received HELLO on Serial0.101 nbr 172.18.0.2
11:39:26:   AS 1, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0

As a note, there are debug commands under both “debug eigrp” and “debug ip eigrp”.

Showing the topology entries for a route helps to figure out the metric calculations, and why one route may be preferred over another one:

r1#show ip eigrp topology 10.0.1.0/24
IP-EIGRP (AS 1): Topology entry for 10.0.1.0/24
  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2313984
  Routing Descriptor Blocks:
  172.18.0.2 (Serial0.101), from 172.18.0.2, Send flag is 0x0
      Composite metric is (2313984/304128), Route is Internal
      Vector metric:
        Minimum bandwidth is 1544 Kbit
        Total delay is 25630 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 2
  192.168.1.93 (Ethernet0), from 192.168.1.93, Send flag is 0x0
      Composite metric is (2339584/2313984), Route is Internal
      Vector metric:
        Minimum bandwidth is 1544 Kbit
        Total delay is 26630 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 3

Those are the big ones… You can get into the details of the packets under debug eigrp packets, or debug eigrp fsm to troubleshoot SIA routes.