Troubleshoot EIGRP

Exam: 642-832 - Troubleshooting and Maintaining Cisco IP Networks (TSHOOT v1.0)

To enable EIGRP on a router and enable neighbor adjacencies, the following information is required:

  • EIGRP Autonomous System Number (defined via "router eigrp [AS#]" command)
  • Interfaces on which to enable EIGRP (defined via "network [IP ADDRESS] [WILDCARD MASK]"

You can verify EIGRP adjacencies by using the "show ip eigrp neighbors" command.

Following steps outline the basic troubleshooting steps for EIGRP neighbor adjacencies:

  1. If the above command displays blank output, make sure that you are using the correct network statement. Note that network statement is used to enable EIGRP on the interface. If you use the network statement without the wildcard mask, the command takes the IP address as the classful network. So, if you use a "network" command without the wildmark mask, EIGRP will be enabled on the whole subnet. If there are multiple interfaces with multiple subnets present on a router, it is recommended that you enable EIGRP on each interface with a wildcard mask.
  2. Ensure that EIGRP adjacencies are being formed on primary IP addresses. Note that EIGRP will NOT form neighbors on secondary IP addresses.
  3. Ensure that neighbors can ping each other upto the interface MTU size. So, if you are network supports 1420 byte MTU, make sure interfaces of both neighbors have the same MTU.
  4. Make sure there are no inbound access lists applied on the EIGRP enabled interfaces. For quick testing you can temporarily remove the ACL to check if EIGRP comes up. If it does, you can adjust the ACL by using the "permit eigrp" clause in the ACL.
  5. Although EIGRP comes up with different hello and hold timers at each neighbor, however, it is recommended that the hold time is at least 3 times hello time.
  6. For route troubleshooting, note that EIGRP stores information in 3 tables. The Interface Table, Topology Table and Neighbor Table. If a route is in topology table but not present in route table then there might be a better route present in the routing table which is preventing eigrp from installing its routes. EIGRP Interface table lists the interfaces that are taking part in EIGRP and can be viewed using "show ip eigrp neighbors"
    EIGRP Neighbor table keeps at track of all EIGRP neighbors and can be viewed using "show ip eigrp neighbors"
    EIGRP Topology Table contains a list of all the EIGRP routes and gives detailed information about metrics, successors and feasible successors.


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