AIS AI2524 Implementation Considerations, Configure Route Summarization between Ospf Areas

AI2524 Router Card User’s Manual

Implementation Considerations

Before implementing this feature, consider these items:

zYou can set a Type 7 default route that can be used to reach exter- nal destinations. When configured, the router generates a Type 7 default into the NSSA by the NSSA ABR.

zEvery router within the same area must agree that the area is NS- SA; otherwise, the routers will not be able to communicate with each other.

zIf possible, avoid using explicit redistribution on NSSA ABR be- cause confusion may result over which packets are being translat- ed by which router.

Configure 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 sequentially, 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, type this command in router configura- tion mode:

area area-id range address mask

Configure Route Summarization When Redistributing

Routes into OSPF

When redistributing routes from other protocols into OSPF, each route is advertised individually in an external link state advertisement (LSA). However, you can configure the Cisco IOS software to adver tise a single route for all the redistributed routes covered by a specified network address and mask. Doing so helps decrease the size of th OSPF link state database.

To have the software advertise one summary route for all redistributed routes covered by a network address and mask, type this command in router configuration mode:

summary-address address mask

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