Monitoring Local Preference Cont

Every physical connection also includes a BGP session. All monitoring and troubleshooting commands were used on router RTR-A.

RTR-A has one internal and two external neighbors. RTR-B is setting local preference 100 for all updates, and RTR-A is setting a default local preference (value 60) for all external updates except for those coming from router RTR-D, where a route-map is used to set a local preference of 90. The following pages show the output of show and debug commands on router RTR-A.

4-32 Configuring BGP on Cisco Routers (BGP) v3.2 © 2005, Cisco Systems, Inc.

The output in the figure contains routes with three different local preference values:

■ Network 10.0.0.0/8 originates locally on RTR-A, and the applied default local preference 60 is not displayed.

■ The second path for network 12.0.0.0/8 was received from RTR-D and received a local preference value of 90 by the route-map.

■ All routes that are received from router RTR-B are marked as internal and have a local preference value of 100 set on RTR-B.

Note The output of the show ip bgp command will not display the local preference value if the value is the same as the bgp default local-preference value in the local router. In the example, RTR-B uses its default local preference value (100). When these routes are propagated to RTR-A, RTR-A displays the local preference value of 100 because it is different from the default local preference value that is configured on RTR-A.

© 2005, Cisco Systems, Inc. Route Selection Using Attributes 4-33

Use the show ip bgp prefix command to see more detailed information about a specific network, including the locally applied default local preference.

In this example, there are three paths to reach the same network:

■ The first path is external and was received from router RTR-C. The new default local preference value 60 was applied to the update.

■ The second path is external and was received from router RTR-D. The route-map was used to set a local preference of 90.

■ The third path is internal and was received from RTR-B. The update already contained a local preference attribute with a value of 100.

Router RTR-A chose the last path as best because it has the highest local preference.

4-34 Configuring BGP on Cisco Routers (BGP) v3.2 © 2005, Cisco Systems, Inc.

Monitoring Local Preference (Cont.)

Monitoring Local Preference (Cont.)

This figure shows the debugging output of incoming BGP updates. Because a router propagates the local preference attribute to other routers in the same AS only, local preference will be associated with routes sent from internal neighbors.

© 2005, Cisco Systems, Inc. Route Selection Using Attributes 4-35

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