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Configuring OSPF
Configuring Route Summarization Between OSPF Areas
IPC-230
Cisco IOS IP Configuration Guide
To control summarization and filtering of type 7 LSAs into type 5 LSAs, use the following command in
router configuration mode on the ABR:
Implementation Considerations
Evaluate the following considerations before you implement this feature:
• You can set a type 7 default route that can be used to reach external destinations. When configured,
the router generates a type 7 default into the NSSA or the NSSA ABR.
• Every router within the same area must agree that the area is NSSA; otherwise, the routers will not
be able to communicate.
Configuring Route Summarization Between OSPF Areas
Route summarization is the consolidation of advertised addresses. This feature causes a single summary
route to be advertised to other areas by an ABR. In OSPF, an ABR will advertise networks in one area
into another area. If the network numbers in an area are assigned in a way such that they are contiguous,
you can configure the ABR to advertise a summary route that covers all the individual networks within
the area that fall into the specified range.
To specify an address range, use the following command in router configuration mode:
Configuring Route Summarization When Redistributing Routes
into OSPF
When routes from other protocols are redistributed into OSPF (as described in the chapter “Configuring
IP Routing Protocol-Independent Features”), each route is advertised individually in an external LSA.
However, you can configure the Cisco IOS software to advertise a single route for all the redistributed
routes that are covered by a specified network address and mask. Doing so helps decrease the size of the
OSPF link-state database.
Command Purpose
Router(config-router)# summary address {ip-address mask |
prefix mask} [not advertise] [tag
tag]
Controls the summarization and filtering during the
translation.
Command Purpose
Router(config-router)# area area-id range ip-address mask
[advertise | not-advertise][cost cost]
Specifies an address range for which a single route
will be advertised.