Border Gateway Protocol - CCIE Routing and Switching Exam Certification Guide - page 436

Example 9-5 shows a BGP community configuration that does not advertise network 2.0.0.0/8
to the external BGP neighbor 1.1.2.5. The community commnolocal does not change or set the
attribute of other networks.

BGP Community Configuration Example Example 9-5

router bgp 100
neighbor 1.1.2.5 remote-as 300
neighbor 1.1.2.5 send-community
neighbor 1.1.2.5 route-map commnolocal out
!
route-map commnolocal permit 10
match ip address 10
set community no-export
!
route-map commnolocal permit 20
match ip address 11
!
access-list 10 permit 2.0.0.0
access-list 11 permit 3.0.0.0
access-list 11 permit 4.0.0.0

BGP Prefix Filter
BGP prefix lists filter routes inbound or outbound to a neighbor. The list filters the routes that
are sent to, or received from, a BGP neighbor. When the route in an update matches an entry in
the prefix list, the router does not need to continue trying to match entries in the list. The result
is that if there are multiple entries in the list that will match a given route, the entries in the top
of the list, which are the entries with the lowest sequence numbers, will be used. An implicit
deny appears at the end of the list for any networks that do not have a match. Example 9-6 shows
a prefix list that filters what routes are included in the route updates to BGP neighbor 1.1.1.1.

BGP Prefix Filter Configuration Example Example 9-6

router bgp 100
neighbor 1.1.1.1 prefix-list ccie out
!
ip prefix-list ccie seq 1 permit 2.0.0.0/8
ip prefix-list ccie seq 2 permit 3.0.0.0/8

BGP Neighbor Distribute Lists
Distribute lists also filter routes inbound or outbound to a neighbor. The list number is specified
in the neighbor command, and access lists specify the networks to filter. Example 9-7 shows a
distribute list that permits two networks from neighbor 1.1.1.1.