Juniper JUNOSE 11.2.X BGP AND MPLS, Configuration Manual

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come to AS 873 from AS 17 than when they come from AS 32. As a result, both router LA
and router SanJose prefer to reach this network through router Boston in AS 17.
bgp default local-preference
•
Use to change the default local preference value.
•
Changes apply automatically whenever BGP subsequently runs the best-path decision
process for a destination prefix; that is, whenever a best route is picked for a given
prefix.
To force BGP to run the decision process on routes already received, you must use the
clear ip bgp command to perform an inbound soft clear or hard clear of the current
BGP session.
•
Use the no version to restore the default value, 100.
•
See bgp default local-preference.
Using a Route Map to Set the Local Preference
When you use a route map to set the local preference you have more flexibility in selecting
routes for which you can set a local preference based on many criteria, including AS. In
the previous section, all updates received by router SanJose were set to a local preference
of 200.
Using a route map, you can specifically assign a local preference for routes from AS 17
that pass through AS 293.
The following commands configure router SanJose.
host2(config-router)# router bgp 873
host2(config-router)# neighbor 10.2.2.3 remote-as 873
host2(config-router)# neighbor 10.5.5.1 remote-as 17
host2(config-router)# neighbor 10.5.5.1 route-map 10 in
host2(config-router)# exit
host2(config)# ip as-path access-list 1 permit ^17 293$
host2(config)# route-map 10 permit 10
host2(config-route-map)# match as-path 1
host2(config-route-map)# set local-preference 200
host2(config-route-map)# exit
host2(config)# route-map 10 permit 20
Router SanJose sets the local-pref attributes to 200 for routes originating in AS 293 and
passing last through AS 17. All other routes are accepted (as defined in instance 20 of
the route map 10), but their local preference remains at the default value of 100, indicating
a less-preferred path.
Understanding the Origin Attribute
BGP uses the origin attribute to describe how a route was learned at the origin—the point
where the route was injected into BGP. The origin of the route can be one of three values:
•
IGP—Indicates that the route was learned by means of an IGP and, therefore, is internal
to the originating AS. All routes advertised by the
network command have an origin of
IGP.
Copyright © 2010, Juniper Networks, Inc. 114
JunosE 11.2.x BGP and MPLS Configuration Guide