In the first part of this series, we subdivided the processes of EIGRP into four discrete steps, and detailed troubleshooting the first two. This is taken from the 5-Day CCNP bootcamp:

  • Discovery of neighbors
  • Exchange of topology information
  • Best path selection
  • Neighbor and topology table maintenance

Let us now discuss path selection and maintenance troubleshooting.

We should all remember that we can view the topology table of EIGRP with the command show ip eigrp topology. Here we can see the successor routes (these are the best routes that are placed in the routing table) and we can see the second best routes, the feasible successor routes. These feasible successor routes are the key to the lightening fast convergence that EIGRP can offer us. When a speaker loses its successor, it can quickly install a feasible successor route in its place.

We need to remember the important rule of feasible successors. The advertised distance of the proposed feasible successor must be less than the feasible distance of the current successor route. This is actually a loop prevention mechanism.

Another big gotcha when it comes to path selection in EIGRP is the configuration of variance to unequal cost load balance. I can remember fighting with this in an INE practice lab long ago when I was preparing for the exam. Something I had no idea of back order to be considered for the unequal load balancing, the alternate paths must be feasible successors! Older editions of CCNP courses never thought to tell us that little nugget!

We should be careful when modifying bandwidth to effect path selection. Cisco gave us delay for this purpose. Modifying the bandwidth can starve EIGRP updates of bandwidth to use. Remember, by default, EIGRP will only use 50% of an interface's bandwidth. We can control this with the command ip bandwidth percent eigrp.

For table maintenance, show ip eigrp topology is critical. Note that in this table, passive is what we want to see. Active indicates there is not a feasible successor and neighbors are being queried for an alternative path. SIA log messages indicate a Stuck in Active issue. Here the router is not receiving a reply to queries. The most common reasons this can occur:

  • Bad link
  • Congested link
  • The query scope if too big (too many routers involved)
  • Excessive redundancy is built into the network
  • The router CPU is overloaded
  • There is a shortage of memory on the router
  • There are software defects

When it comes to table maintenance, another excellent troubleshooting command is show ip eigrp topology summary. This command displays the total number of routes in the topology table and the total number of queries the router is waiting on responses for. It also shows a quiescent interface field that shows which interface have no outstanding packets to be sent or acknowledged.

Some of our favorite EIGRP verification commands:

  • show ip route eigrp
  • show ip protocol
  • show ip eigrp neighbor
  • show ip eigrp topology
  • show ip eigrp topology all-links
  • show ip eigrp topology summary
  • debug eigrp packet hello
  • debug eigrp packet query reply

We are so excited here at INE for the live, online 5-Day CCNP bootcamp that starts Monday, August 16, 2010 . I look forward to seeing many of our aspiring CCIE candidates in this course. These students realize that they really need to improve their foundation Tier 1 knowledge as they seek to conquer the Lab Exam beast.

In this blog post, we are going to provide a sneak peek into some of the awesome information shared in the TSHOOT section of the bootcamp regarding the Troubleshooting of EIGRP. This can prove critical in the Troubleshooting and Configuration sections of the CCIE R&S Lab Exam, as well as the TSHOOT CCNP exam (duh!).

Where Is My Neighbor!?!?!?

The first thing that you want to master when it comes to troubleshooting EIGRP is the 'workflow" that EIGRP follows in its operation. We can subdivide the processes of this exciting protocol into four discrete steps:

  • Discovery of neighbors
  • Exchange of topology information
  • Best path selection
  • Neighbor and topology table maintaince

Discovery of Neighbors

Remember that EIGRP discovers neighbors through bi-directional multicast by default. IP protocol 88 and are the key parameters we need to watch out for here. Could there be issues with NBMA pseudo-broadcast support or filtering causing neighbor discovery to fail? Certainly things to examine in the topology. Also, watch out for the neighbor command under the EIGRP routing process. This feature causes the use of unicast packets for neighbor creation exclusively and must be agreed upon by BOTH neighbors.

Another area we need to be aware of is the attributes that must match in order for neighbors to form. Sure this list is nowhere near as lengthy as the parameters that we have to watch out for in OSPF networks, but the list is just as critical:

  • Common Subnet (Must be the primary address - not a secondary)
  • Autonomous System Number
  • Authentication
  • K values (metric weights)

Exchange of Topology Information

When it comes to the exchange of topology information, this is done with unicast. Notice that connectivity for neighborship still requires mutlicast communications (unless you are using the neighbor command).

Remember that EIGRP will only advertise those prefixes that it installs in the routing table. This is an excellent time to review the difference from the Topology Table to the Routing Table.

Important troubleshooting considerations for the exchange of topology information include:

  • Automatic summarization in use?
  • Split horizon settings
  • The use of duplicate router IDs preventing external route introduction
  • No seed metric set for external prefixes
  • Filtering through the use of distribute lists

Please consider these troubleshooting aspects for these two phases of EIGRP's operation. We will cover more in the next installment coming soon...


Our student and friend Deepak Arora was kind enough to share these sample TSHOOT exam questions in the IEOC.Thanks again, Deepak!

Enjoy everyone. The interface is pretty self explanatory, and as you can see, Cisco is combining several previous flash-based, written exam elements into one here. If you do need assistance with it, I copied the instructions link here as well.

We are working hard on the exciting new TSHOOT course, and yes, it will be made available free of charge to all of our existing CCNP students as part of our Investment Protection Program.

TSHOOT Exam Demo

TSHOOT Exam Instructions

Also, we will be announcing a date of release soon.


Many students are getting excited for the new CCNP here at INE - and these students are not just those interested in pursuing their CCNP certification. The new TSHOOT course is certainly going to compliment our best-selling Advanced Troubleshooting Bootcamp for those students pursuing their CCIE R&S.

Here is the list of specific technologies this new course will aid us in troubleshooting:

  • OSPF
  • eBGP
  • Redistribution
  • DHCP Client and Server
  • NAT
  • IPv6 Routing
  • IPv6 Transition Techniques
  • L2 Trunking
  • L2 STP
  • L2 DTP
  • Private VLANs
  • Port Security
  • Switch Security
  • L2 SVIs
  • Supervisor Redundancy
  • Switch Support of Wireless, VOIP, and Video
  • Router Security
  • ACLs
  • AAA
  • IOS Service Security
    Troubleshoot EIGRP
    Troubleshoot OSPF
    Troubleshoot eBGP
    Troubleshoot routing redistribution solution
    Troubleshoot a DHCP client and server solution
    Troubleshoot NAT
    Troubleshoot first hop redundancy protocols
    Troubleshoot IPv6 routing
    Troubleshoot IPv6 and IPv4 interoperability
    Troubleshoot switch-to-switch connectivity for the VLAN based solution
    Troubleshoot loop prevention for the VLAN based solution
    Troubleshoot Access Ports for the VLAN based solution
    Troubleshoot private VLANS
    Troubleshoot port security
    Troubleshoot general switch security
    Troubleshoot VACL and PACL
    Troubleshoot switch virtual interfaces (SVIs)
    Troubleshoot switch supervisor redundancy
    Troubleshoot switch support of advanced services (i.e., Wireless, VOIP and Video)
    Troubleshoot a VoIP support solution
    Troubleshoot a video support solution
    Troubleshoot Layer 3 Security
    Troubleshoot issues related to ACLs used to secure access to Cisco routers
    Troubleshoot configuration issues related to accessing the AAA server for authentication purposes
    Troubleshoot security issues related to IOS services (i.e.,finger, NTP, HTTP, FTP, RCP etc.)

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