Cisco Cisco IOS Software Release 12.4(15)T

Before this feature is configured, the OSPF routing protocol must be configured.

This feature is available only for IP Version 4 networks.

Before you configure this feature, you should understand the following concept:

A router that is running OSPFv2 maintains a local RIB in which it stores all routes to destinations that 
it has learned from its neighbors. At the end of each SPF, OSPF attempts to install the best (that is, the 
least-cost) routes to a destination present in the local RIB into the global IPv4 routing table. The global 
RIB will be updated only when routes are added, deleted, or changed. Routes in the local RIB and 
Forwarding Information Base (FIB) will not compute when intermediate results are computed during 
SPF, resulting in fewer dropped packets in some circumstances.

Although it is recommnded to keep the default settings for the commands described in the following 
sections, it is optional to change the defaults settings. This section describes the following otional tasks:

 (optional)

 (optional)

By default, the contents of the global RIB are used to compute inter-area summaries, NSSA translation, 
and forwarding addresses for type-5 and type-7 LSAs. Each of these functions can be configured to use 
the contents of the OSPF local RIB instead of the global RIB for their computation. Using the local RIB 
for the computation may be slightly faster in some circumstances, but because the local RIB has 
information for only a particular instance of OSPF, using it for the computation may yield incorrect 
results. Potential problems that may occur include routing loops and black-hole routes. It is 
recommended that you not change the default values because they are conservative and preserve the 
current global RIB behavior.