Configuring OSPF Route Aggregation
Context
Route summarization on a large-scale OSPF network efficiently reduces routing entries. This function minimizes consumption of system resources while maintaining system performance. In addition, if a specific link frequently alternates between Up and Down states, the links uninvolved in the route summarization will not be affected. This prevents route flapping and improves network stability.
When an ABR sends routing information to other areas, it originates Type 3 LSAs for each network segment. If any contiguous segments exist in this area, run the abr-summary command to summarize these segments into one. An ABR then sends just one summarized LSA to other areas, and no LSAs that belong to the summarized network segment specified by this command. Therefore, the routing table size is reduced, and router performance is improved.
Carry out the following steps on the router running OSPF.
Procedure
- Configuring ABR route aggregation
- Configuring ASBR route aggregation
- Run asbr-summary ip-address mask [ not-advertise | tag tag | cost cost | distribute-delay interval ] *
ASBR route aggregation is configured.
After route summarization is configured, the routing table on the local OSPF router remains unchanged. The routing table on another OSPF router, however, contains just one summarized route, and no specific routes. This summarized route will not be removed unless all specific routes are interrupted.
- Run asbr-summary ip-address mask [ not-advertise | tag tag | cost cost | distribute-delay interval ] *
