Juniper JUNOSE, Руководство по настройке

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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.
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Use the no version to restore the default value, 100.
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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:
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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.
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EGP—Indicates that the route was learned by means of an EGP.
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Incomplete—Indicates that the origin of the route is unknown—that is, learned
from something other than IGP or EGP. All routes advertised by the
redistribute
command—such as static routes—have an origin of Incomplete. An origin of
Incomplete occurs when a route is redistributed into BGP.
Selecting the Best Path
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Chapter 1: Configuring BGP Routing