Isolating the problem methodology

Although this module will describe many common problems and solutions for troubleshooting various routing protocols, it is important to note that there is no single template for solving Layer 3 problems. Routing problems are solved with a methodical process, using a series of commands to isolate and diagnose the problem.

Many of the examples in this module are just that, examples. It is important to be able to apply these examples and concepts to other routing protocols and other scenarios.

Here are some areas to explore when diagnosing a possible problem involving routing protocols:

General Network Issues
Many times a change in the topology, such as a down link, may have other affects on other areas of the network which might not be obvious at the time. This may include the installation of new routes, static or dynamic, removal of other routes, and so on.

Some of the things to consider include:

  • Has anything in the network changed recently?
  • Is there anyone currently working on the network infrastructure?

Connectivity Issues
Check for any equipment and connectivity problems including:

  • Power problems: outages, intermittent problems, environmental problems such as overheating, and so on.
  • Layer 1 problems: cabling problems, bad ports, service provider problems, and so on.

Some commands, which can be used to check these and other issues, include:

  • ping
  • traceroute
  • show interfaces , show ip interface

Neighbor Issues
If the routing protocol establishes an adjacency with a neighbor, check to see if there are any problems with the routers forming neighbor relationships.

Topology Database
If the routing protocol uses a topology table or database, check the table for anything unexpected, such as missing entries or unexpected entries.

Routing Table
Check the routing table for anything unexpected, such as, missing routes or unexpected routes. Use debug commands to view routing updates and routing table maintenance.

Many troubleshooting issues and solutions are common amongst different routing protocols. In this module, some issues described on one routing protocol may also apply to others.

Lab Activity

Lab Exercise: Correcting Problems at the Network Layer

In this lab, the student will use various Cisco commands to correct network problems.