BGP Local Preference Cont

• Local preference is the second strongest BGP route selection parameter.

• Remember the BGP route selection rules:

- Highest weight preferred (local to router)

- Highest local preference preferred (global within AS)

- Other BGP route selection rules

• Weights configured on a router override local preference settings.

• To ensure consistent AS-wide route selection:

- Do not change local preference within the AS.

- Do not use BGP weights.

Local preference is the second-strongest BGP route selection parameter. Remember the route selection rules:

1. Prefer the highest weight (local to router).

2. Prefer the highest local preference (global within AS).

3. Process all remaining BGP route selection rules.

Because network administrators can use both weight and local preference to manipulate the route selection process, they must decide which one to use. If local preference is used, the weight should be the same for all paths.

Network administrators can use weight on an individual router to override local preference settings that are used in the rest of the AS.

In most cases, it is enough to change the default local preference on updates coming from external neighbors. Network administrators should avoid changing the local preference attribute on internal sessions to prevent unnecessary complexity and unpredictable behavior.

© 2005, Cisco Systems, Inc. Route Selection Using Attributes 4-25

BGP Local Preference (Cont.)

Network administrators can apply local preference in the following ways:

■ Use a route-map with the set local-preference command. You can use the route-map on incoming updates from all neighbors or on outgoing updates to internal neighbors (not recommended).

■ Use the bgp default local-preference command to change the default local preference value that is applied to all updates that come from external neighbors or that originate locally.

4-26 Configuring BGP on Cisco Routers (BGP) v3.2 © 2005, Cisco Systems, Inc.

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