Advertising Local Networks - HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual

IP Routing—Configuring RIP, OSPF, BGP, and PBR
Configuring BGP

Advertising Local Networks

Specify the local networks that remote sites should be able to access. You
should only advertise networks that originate in your AS. To allow BGP to
advertise a network, enter the following command:
Syntax: network <A.B.C.D> mask <subnet mask>
For example, if you want the router to advertise the private network 10.1.10.0
/24, enter:
ProCurve(config-bgp)# network 10.1.10.0 mask 255.255.255.0
BGP is a classless protocol. You can specify networks with variable-length
subnet masks.
Note that the router is actually advertising a route, not a network. BGP can
therefore send out a route summary for the entire range of local subnets. For
example, Site A includes 16 /24 networks from 10.1.0.0 /24 to 10.1.15.0 /24,
which together make up network 10.1.0.0 /20. You can specify the entire range
of subnets by entering:
ProCurve(config-bgp)# network 10.1.0.0 mask 255.255.240.0
Because the BGP router is advertising a route, it searches its routing table for
a route to the specified networks. It then sends this route to all authorized
neighbors.
Remember that the subnet mask is an integral part of the network address. If
you specify that the BGP interface advertise routes to network 10.1.0.0 /20, it
will not advertise routes to network 10.1.0.0 /16 or to network 10.1.0.0 /24.
Therefore, when you advertise a network or range of networks, you must
verify that the routing table includes the exact route that you have specified
(including the same subnet mask or corresponding prefix length.)
If the routing table does not include this route, you must configure a null route.
For example, Router A's routing table only includes routes to the 24-bit
networks, not to the 20-bit network that contains them all. You must manually
add a route to network 10.1.0.0 /20 so that the BGP interface can advertise it.
Enter the route from the global configuration mode context. Use the null
keyword for the next-hop address:
ProCurve(config)# ip route 10.1.0.0 /20 null 0
You do not have to worry about the router misdirecting local traffic because
the router always uses the most specific entry in the table to route packets.
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