Configuring the Open Shortest Path First Protocol
20-33
20
CLI - This example configures the backbone area and one transit area.
Configuring Summary Addresses (for External AS Routes)
Redistributing routes from other protocols into OSPF normally requires the router to
advertise each route individually in an external LSA. An Autonomous System
Boundary Router (ASBR) can be configured to redistribute routes learned from other
protocols into all attached autonomous systems. (See “Redistributing External
Routes” on page 20-35.)
To reduce the amount of external LSAs sent to other autonomous systems, you can
configure the router to advertise an aggregate route that consolidates a broad range
of external addresses. This helps both to decrease the number of external LSAs
advertised and the size of the OSPF link state database.
Command Usage
• If you are not sure what address ranges to consolidate, first enable external route
redistribution via the Redistribute Configuration screen, view the routes imported
into the routing table, and then configure one or more summary addresses to
reduce the size of the routing table and consolidate these external routes for
advertising into the local domain.
• To summarize routes sent between OSPF areas, use the Area Range
Configuration screen (page 20-23).
Command Attributes
• IP Address – Summary address covering a range of addresses.
• Netmask – Network mask for the summary route.
Note:
This router supports up 16 Type-5 summary routes.
Console(config-router)#network 10.0.0.0 255.0.0.0 area 0.0.0.0 42-26
Console(config-router)#network 10.1.1.0 255.255.255.0 area 0.0.0.1
Console(config-router)#end
Console#show ip ospf 42-39
Routing Process with ID 10.1.1.253
Supports only single TOS(TOS0) route
Number of area in this router is 4
Area 0.0.0.0 (BACKBONE)
Number of interfaces in this area is 1
SPF algorithm executed 8 times
Area 0.0.0.1
Number of interfaces in this area is 1
SPF algorithm executed 5 times
Area 0.0.0.2 (STUB)
Number of interfaces in this area is 1
SPF algorithm executed 13 times
Area 0.0.0.3 (NSSA)
Number of interfaces in this area is 1
SPF algorithm executed 12 times
Console#
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