HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual page 705

IP Routing—Configuring RIP, OSPF, BGP, and PBR
Configuring BGP
Remember that the local router's routing table must include this exact route
in order for the router to advertise it. If your network uses subnetted networks,
you may need to add a null route to the range of subnets. For example:
ProCurve(config)# ip route 10.1.0.0 /16 null 0
If you want the router to advertise separate routes for the subnets, you must
permit the address for the complete network and then specify the bit length
prefix for the subnets. For example, to configure the router to advertise /20
networks subnetted from the 10.1.0.0 /16 network, enter:
ProCurve(config)# ip prefix-list LAN1 seq 10 permit 10.1.0.0/16 ge 20 le 20
You could also specify a range of prefix lengths for routes to variable length
subnets:
ProCurve(config)# ip prefix-list LAN1 seq 10 permit 10.2.0.0/16 ge 18 le 24
You can, of course, also use the command to deny routes. For example, to
configure a prefix list to prevent advertisement of any /24 subnet in the 10.2.0.0
/16 network, enter:
ProCurve(config)# ip prefix-list LAN1 seq 10 deny 10.2.0.0/16 ge 24 le 24
In this case, the router could still advertise routes to subnets with a different
prefix length—for example, to 10.2.0.0 /16 or to 10.2.16.0 /20.
For a more detailed explanation of the many options available for specifying
routes in a prefix list, see "Creating Prefix Lists: Configuring Filters for Route
Exchange" on page 13-78.
After configuring the prefix list, match it to the route map. Create a route map
entry and enter this command:
Syntax: match ip address prefix-list <listname>
When you have finished configuring the route map, apply the map to the BGP
neighbor as an outbound policy. (See "Applying a Route Map Entry to a BGP
Neighbor" on page 13-104.)
Filtering Advertised Routes According to Community. If your network
places routes in communities, you can filter the routes that the local router
advertises according to these communities.
A route can be a member of one or more communities. A community is simply
a way of grouping routes together and applying a consistent policy to the
group. In order for a route's membership in a community to mean anything,
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