HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual page 667

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The ASBR's OSPF database must include the external networks in order to
advertise summaries for them. Therefore, you must redistribute RIP routes
into OSPF in order for the summary-address command to take effect.
One situation in which you could configure route summaries is when a router
connects to a network at a remote site using an exterior gateway protocol.
Perhaps the site uses a different routing protocol, so routes to this site must
be treated as external routes. However, these routes will not be so extensive
as those to a public network such as the Internet, and you do not want to
advertise only one default route for all of them. Or the router in a virtual private
network (VPN) may receive routes from an ISP router that the ISP has
tunneled from a remote site.
For example, suppose that a router receives an external route for a network
that uses private addresses in 10.2.0.0 /16 range. Enter this command to enable
the router to advertise these networks to routers in the OSPF network:
ProCurve(config-ospf)# summary-address 10.2.0.0 255.255.0.0
You can also specify that the ASBR not advertise routes to that range of
external addresses with the not-advertise option.
Another reason you might want your ASBR to advertise route summaries
rather than a default route is that your organization multihomes—that is, it
connects to more than one ISP. One ASBR can advertise part of the Internet
address space, and the other can advertise the rest. Routers will then balance
external traffic over both the connections to the Internet. (See "Load Balanc-
ing" on page 13-74 for a more detailed discussion of load balancing with BGP.)
To configure an ASBR to advertise only half of the Internet address space,
enter:
ProCurve(config-ospf)# summary-address 0.0.0.0 128.0.0.0
ProCurve(config-ospf)# summary-address 128.0.0.0 128.0.0.0 not-advertise
Do not confuse the summary-address command with the area <area ID>
range command. The first is for summary LSAs to external networks; the
second is for summaries to networks in an internal area.
IP Routing—Configuring RIP, OSPF, BGP, and PBR
Configuring OSPF
13-53