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BGP: Route Map Filtering Example
Page 48 | Use Route Maps and Other Filters to Filter and Alter BGP and OSPF Routes
BGP: Route Map Filtering Example
Here is an example of a set of route maps.
BGP configuration
First, we need to set the router’s ASN and the ASN of the peer.
router bgp 3816
neighbor 172.26.1.1 remote-as 15557
neighbors are enabled by default.
Route map configuration
Next, we want to limit the routes that we accept from this peer. We will accept the default
route from any community, but will only accept any other updates from community 15557.
ip prefix-list plist1 seq 1 permit 0.0.0.0/0
ip community-list 1 permit 15557
route-map accDef15557 permit 1
match ip address prefix-list plist1
route-map accDef15557 permit 2
match community 1 exact-match
router bgp 3816
neighbor 172.26.1.1 route-map accDef15557 in
Next, we want to change the attributes of certain routes before advertising them to the
neighbor 172.26.1.v. For 192.168.2.0/24, we will add to the AS path. For 192.168.3.0/24 and
192.168.4.0/24, we will add a different set of entries to the AS path, and set the community
and the local preference. All other routes will be advertised unchanged this neighbor.
ip prefix-list plist2 seq 1 permit 192.168.2.0/24
ip prefix-list plist3 seq 1 permit 192.168.3.0/24
ip prefix-list plist4 seq 1 permit 192.168.4.0/24
route-map outdef permit 1
match ip address prefix-list plist2
set as-path prepend 1645
route-map outdef permit 2
match ip address prefix-list plist3
set as-path prepend 65501 63901 43312
set community 0:23445 0:33445 no-advertise