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IP R
OUTING
3-313
Configuring Area Ranges (Route Summarization for ABRs)
An OSPF area can include a large number of
nodes. If the Area Border Router (ABR) has
to advertise route information for each of
these nodes, this wastes a lot of bandwidth
and processor time. Instead, you can
configure an ABR to advertise a single summary route that covers all the
individual networks within its area. When using route summaries, local
changes do not have to be propagated to other area routers. This allows
OSPF to be easily scaled for larger networks, and provides a more stable
network topology.
Command Usage
• Use the Area Range Configuration page to summarize the routes for an
area. The summary route for an area is defined by an IP address and
network mask. You therefore need to structure each area with a
contiguous set of addresses so that all routes in the area fall within an
easily specified range. This router also supports Variable Length Subnet
Masks (VLSMs), so you can summarize an address range on any bit
boundary in a network address.
• To summarize the external LSAs imported into your autonomous system
(i.e., local routing domain), use the Summary Address Configuration
screen (page 3-325).
Console#show ip ospf 4-364
Routing Process with ID 192.168.1.253
Supports only single TOS(TOS0) route
Number of area in this router is 3
Area 0.0.0.0 (BACKBONE)
Number of interfaces in this area is 1
SPF algorithm executed 40 times
Area 0.0.0.2 (STUB)
Number of interfaces in this area is 1
SPF algorithm executed 8 times
Area 0.0.0.3 (NSSA)
Number of interfaces in this area is 1
SPF algorithm executed 40 times
Console#
areaarea
ABR
summary
route