Configuring Route Summaries For Asbrs - HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual

IP Routing—Configuring RIP, OSPF, BGP, and PBR
Configuring OSPF
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The default route may come from one of three sources:
The routing table includes a static default route.
The router has received a default route from the external network. For
example, the WAN interface may receive an IP address and default route
from the remote router in the external network.
The router generates its own default route.
If the routing table already includes a default route (the first two options
described above), you do not need to enter the always keyword with the
default-information-originate command. The always keyword configures
the router to generate the default route even when it does not have its own
default route.
You can set the metric for the default route using the metric keyword. If you
do not enter a value, the default metric is 10. Valid metric values are between
0 and 16,777,214.
The metric-type option specifies how the cost is calculated. External Type 1
(E1) routes take both the external cost and the internal cost (the cost of
reaching the ASBR) into account. External Type 2 (E2) routes include only
the external cost. If you do not enter an option, default routes are defined as
E2 routes.
Generating default routes is often the best solution for an ASBR that connects
to the Internet, particularly when the ASBR provides the only Internet
connection.

Configuring Route Summaries for ASBRs

Instead of transmitting a single default route for all external traffic, an ASBR
can send summaries for ranges of external network addresses. Enter this
command for the destination network or range of networks to be advertised
in each summary:
Syntax: summary-address <A.B.C.D> <subnet mask | /prefix length> [not-advertise]
You should enter the command without the not-advertise option to allow
the router to transmit the external routes to other OSPF routers. Use the not-
advertise option to prohibit the advertisement. In this case, routers will not
be able to reach these external networks unless they have also received a
default route for all external traffic.