Chapter 19
| Unicast Routing
Configuring the Open Shortest Path First Protocol (Version 2)
– 732 –
Figure 496: Displaying Information on NSSA and Stub Areas
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 use the Routing Protocol > OSPF >
Area Range (Add) page to 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.
Figure 497: Route Summarization for ABRs
Command Usage
â—† Use the Area Range configuration page to summarize intra-area routes, and
advertise this information to other areas through Area Border Routers (ABRs).
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. If it is not possible
to use one contiguous set of addresses, then the routes can be summarized for
several area ranges.This router also supports Variable Length Subnet Masks
(VLSMs), so you can summarize an address range on any bit boundary in a
network address.
â—† To summarize the external LSAs imported into your autonomous system (i.e.,
local routing domain), use the Summary Address configuration screen
(page 732).
â—† This router supports up five summary routes for area ranges.
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