Scope the network topology

It is nearly impossible to troubleshoot any type of CEF issue or network connectivity issue without a network diagram that depicts IP addresses, IP routes, devices such as firewalls and switches, and so on. Troubleshooting IP connectivity problems without the aid of a visual topology is nearly impossible unless you can localize the issue to a specific router or switch. In large IP routing scenarios, a network topology is required to troubleshoot connectivity problems. Generally, both logical and physical topologies aid in troubleshooting. Figure 4-1 illustrates a sample physical topology.

Figure 4-1 Sample Network Topology

Learn how to troubleshoot Cisco's Express Forwarding network switching technology in "Basic IP Connectivity and CEF Troubleshooting," Chapter 4 from the book Cisco Express Forwarding by Nakia Stringfield, Russ White and Stacia McKee.

Basic IP Connectivity and CEF Troubleshooting

  Introduction
  Accurately describe the problem
  Scope the network topology
  Review the OSI model for troubleshooting
  Verify the ARP table
  Verify the IP routing table
  Verify the CEF FIB table
  Verify the adjacency table
  Conduct hardware-specific troubleshooting

Reproduced from the book Cisco Express Forwarding. Copyright 2007, Cisco Systems, Inc. Reproduced by permission of Pearson Education, Inc., 800 East 96th Street, Indianapolis, IN 46240. Written permission from Pearson Education, Inc. is required for all other uses.