Juniper JUNOSE 11.2.X BGP AND MPLS, Configuration Manual

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host1(config-router)# neighbor 10.2.9.2 filter-list 1 in
host1(config-router)# neighbor 10.2.8.2 remote-as 11
host1(config-router)# neighbor 10.2.8.2 filter-list 2 in
host1(config-router)# neighbor 10.2.7.2 remote-as 435
host1(config-router)# neighbor 10.2.7.2 filter-list 3 out
host1(config-router)# exit
host1(config)# ip as-path access-list 1 deny ^621_11$
host1(config)# ip as-path access-list 1 permit .*
host1(config)# ip as-path access-list 2 deny ^11_621$
host1(config)# ip as-path access-list 2 permit .*
host1(config)# ip as-path access-list 3 deny ^11_621_282
host1(config)# ip as-path access-list 3 deny ^621_11_282
host1(config)# ip as-path access-list 3 permit .*
AS-path access list 1 is applied to routes that router London receives from router Paris.
Router London rejects routes with the AS path (621 11).
AS-path access list 2 is applied to routes that router London receives from router Berlin.
Router London rejects routes with the AS path (11 621) or (621 282 11).
Router London accepts routes with the AS path (11 282), (621 282), (621 11 282), or (11
621 282). However, it applies AS-path access list 3 to routes it forwards to router Madrid,
and filters out routes with the AS path (621 11 282) or (11 621 282).
Example 2 Consider the following commands used to configure router Chicago in Figure 24 on
page 87:
host1(config)# router bgp 293
host1(config-router)# neighbor 10.5.5.2 remote-as 32
host1(config-router)# neighbor 10.5.5.2 filter-list 1 in
host1(config-router)# neighbor 10.2.2.4 remote-as 17
host1(config-router)# exit
host1(config)# ip as-path access-list 1 deny ^32$
Figure 24: Assigning a Filter List
Access list 1 denies routes that originate in AS 32—and therefore routes originated by
router NY—because the AS-path attribute for these routes begins with (and indeed
consists only of) the value 32.
Routes originating anywhere else—such as in AS 837, AS 17, or AS 451—are permitted,
because their AS-path attributes do not begin with 32.
87 Copyright © 2010, Juniper Networks, Inc.
Chapter 1: Configuring BGP Routing