Install guide

2-36 Release Note
Software Version 2.7.5
C613-10454-00 REV A
Filtering Before Advertising Routes with BGP:
Using an AS Path Filter
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 outpathfilter filter on a BGP peer. It filters transmitted
BGP update messages on the basis of their AS path attributes. Therefore, this
example stops the peer from learning routes that originated in a particular AS.
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 exclude="550$"
2. Apply the AS path list to the BGP peer.
set bgp peer=10.0.0.1 outpathfilter=1
By default, the peer receives all update messages that do not match the
path filter.