Configuration Example 1; Figure 3: Filtering With As-Path Access Lists - Juniper IP SERVICES - CONFIGURATION GUIDE V 11.1.X Configuration Manual

JUNOSe 11.1.x IP Services Configuration Guide

Configuration Example 1

Consider the network structure in Figure 3 on page 24.
Suppose you want router London to behave in the following way:

Figure 3: Filtering with AS-Path Access Lists

The following commands configure router London to apply filters based on AS path
to routes received from router Berlin and router Paris and to routes forwarded to
router Madrid.
AS-path access list 1 is applied to routes that router London receives from router
Paris. Router London rejects routes with the AS path 11 621 or 11 282 621.
24
Access Lists
Accept routes originated in AS 621 only if they pass directly to router London.
Accept routes originated in AS 11 only if they pass directly to router London.
Forward routes from AS 282 to AS 435 only if they pass through either AS 621
or AS 11, but not both AS 621 and AS 11.
host1(config)#router bgp 47
host1(config-router)#neighbor 10.2.9.2 remote-as 621
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 ^11
host1(config)#ip as-path access-list 1 permit .*
host1(config)#ip as-path access-list 2 deny ^621
host1(config)#ip as-path access-list 2 permit .*
host1(config)#ip as-path access-list 3 deny [621 11]
host1(config)#ip as-path access-list 3 permit .*