Dial Configuration Guide, Cisco IOS Release 15.5M&T

CEF Switching Across Dialer Interfaces

The Asynchronous Line Monitoring feature feature introduced in Cisco IOS Release 12.3(4)T adds support for CEF switching across dialer interfaces on Cisco 7500 routers with an RSP.

CEF switching on dialer profile interfaces allows packets to be CEF switched across the interface, rather than fast switched or process switched. CEF switching avoids the overhead of continuous cache cycles by using a Forwarding Information Base (FIB) to make the destination switching decision. The FIB mirrors the contents of the IP routing table, that is, there is a one-to-one correspondence between FIB table entries and routing table prefixes and, therefore, no need to maintain a separate route cache.

This FIB provides significant benefits in terms of performance, scalability, network resilience, and functionality, particularly in large complex networks with dynamic traffic patterns. CEF switching is less CPU-intensive than fast switched route caching. More CPU processing power can be dedicated to Layer 3 services such as quality of service (QoS) and encryption.

CEF switching also offers an unprecedented level of switching consistency and stability in large dynamic networks. In dynamic networks, fast-switched cache entries are frequently invalidated due to routing changes. These changes can cause traffic to be process switched using the FIB routing table, rather than fast switched using the route cache. Because the FIB lookup table contains all known routes that exist in the routing table, it eliminates route cache maintenance and the fast-switch or process-switch forwarding scenario. CEF can switch traffic more efficiently than typical demand caching schemes.

Verifying that Asynchronous Line Monitoring feature Feature Is Operational

Perform the following task to verify that the Asynchronous Line Monitoring feature feature is operational.

SUMMARY STEPS

1. enable

2. debug ip cef { drops [ rpf [ access-list ]] [ access-list ] | receive [ access-list ] | events [ access-list ] | interface | dialer }

3. show adjacency [ type number ] [ detail ] [ summary ] [ internal ]

4. show ip interface [ type number ]

5. exit

DETAILED STEPS

Recording CEF Events for Dialer Interface: Example

The following is a sample record of dialer CEF events on a dialer interface reported by the debug ip cef dialer command:

Displaying CEF Adjacency Table for Dialer Interface: Example

The following is sample output from the show adjacency dialer1 internal command for a dialer profile that indicates where adjacency for the dialer interface is updated:

Displaying CEF Switching Status on IP Dialer Interface: Example

The following is sample output from the show ip interface dialer1 command. Reports about CEF switching on the dialer interface are shown in bold text, for purpose of example.

Related Documents

Standards

MIBs

RFCs

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