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Basic IP Connectivity and Troubleshooting in Cisco Express Forwarding

Chapter Description

This chapter presents the general troubleshooting used on Cisco IOS routers and switches as a first step in troubleshooting IP connectivity problems. It helps you verify whether CEF is the root cause of a particular IP connectivity problem.

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Understanding CEF Error Messages

With current-generation Cisco IOS routers and Catalyst switches, some error messages pertaining to CEF are platform specific. As a result, you need to understand platform differences when troubleshooting CEF error messages. Nevertheless, Table 4-5 lists the general CEF EXEC error messages applicable to all Cisco IOS routers and Catalyst switches when configuring CEF and CEF features.

Table 4-5. General CEF EXEC Error Messages

Error Message

Troubleshooting Action

Must enable IP routing first.

When enabling CEF, IP routing must be enabled first.

Cannot disable CEF on this platform.

When disabling CEF, some platforms, such as the Catalyst 6500, do not support disabling CEF.

CEF is not enabled.

When attempting to configure a global configuration command that requires CEF, CEF must first be enabled.

CEF not enabled on this interface. Enable first.

When attempting an interface configuration that requires CEF, CEF must be enabled first.

A useful tool when working with CEF error messages is the Error Message Decoder on Cisco.com found at the following website (you must be a registered Cisco.com user):

www.cisco.com/cgi-bin/Support/Errordecoder/index.cgi

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