HP 7102dl - ProCurve Secure Router Configuration Manual page 822

IP Routing—Configuring RIP, OSPF, BGP, and PBR
Configuring BGP
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Private networks do not typically transit traffic between AS. Therefore, filter-
ing advertised routes according to AS path is usually unnecessary when
configuring eBGP in a private network.
To select routes according to values in their AS fields, first create the AS list:
Syntax: ip as-path-list <listname>
Then enter this command:
Syntax: [deny | permit] <string of AS numbers>
For example, you can permit the router to advertise only routes that use AS 1
and 2:
ProCurve(config-as-path-list)# permit 1 2
Remember that this statement only permits routes that use both AS 1 and AS 2.
If you want to permit any routes that use either AS, you should enter separate
statements:
ProCurve(config-as-path-list)# permit 1
ProCurve(config-as-path-list)# permit 2
Permitting AS number 1 selects any routes that include that value, even if the
AS field also includes other values. In other words, entering permit 1 permits
routes through AS 1 and routes through AS 1 and AS 2, while entering permit
1 2 only permits routes through both AS 1 and AS 2. Therefore, you may need
to explicitly deny any values that should not be included in the field.
For example, if you allow the router to advertise routes that use AS 1, routes
that use AS 1 and AS 3, will also be allowed. If you do not want to allow such
routes, you must specifically deny AS 3.
You could also allow the router to advertise routes that use AS 1 or AS 2, but
not routes that force traffic to travel through both AS 1 and AS 2:
ProCurve(config-as-path-list)# deny 1 2
ProCurve(config-as-path-list)# permit 1
ProCurve(config-as-path-list)# permit 2
Remember to enter the deny statement before the permit statements since the
router processes statements in the AS path list in the order that you enter them.
After configuring the AS path list, create the route map entry that will filter
the routes. Then enter this route map configuration mode command:
Syntax: match as-path <listname>