Install guide

Filtering IP Routes 2-37
Software Version 2.7.5
C613-10454-00 REV A
Filtering Before Advertising Routes with BGP:
Using a Route Map
This example extends the basic BGP configuration shown in Basic BGP
Configuration in the BGP chapter of the Software Reference, which connects
two routers or switches as EBGP peers and gives:
■ Router or Switch A an IP address of 10.0.0.2 and AS number of 65000
■ Router or Switch B an IP address of 10.0.0.1 and AS number of 65001
This example uses the outroutemap filteron a BGP peer. The outroutemap
filter is applied after all other filters have acted on an update message. This
particular route map filters transmitted BGP update messages on the basis of
their AS path attributes. It acheives the same effect as the previous “Filtering
Before Advertising Routes with BGP: Using an AS Path Filter” example.
Route map filters are sometimes more useful than path filters because route
maps can modify the attributes of a received BGP update message. Path filters
only include or exclude messages. However, this example does not
demonstrate how to modify the message attributes, because it is meaningless
to modify attributes and then discard the message.
To stop Router or Switch A from advertising update messages to a peer,
when the update messages originate from AS 550
1. Add an AS path list entry.
add ip aspathlist=2 entry=1 include="550"
2. Add a route map entry.
add ip routemap=as550 entry=1 match aspathlist=2
action=exclude
This entry matches AS paths that are included in the path list, and excludes
them.
3. Apply the route map to the BGP peer.
set bgp peer=10.0.0.1 outroutemap=as550
By default, the peer receives all update messages that do not match the
route map.