Optimal Configuration of OSPF Aggregates

Open Shortest Path First (OSPF) is a popular protocol for routing within a autonomous system domain. In order to scale for large networks containing hundreds and thousands of subnets, OSPF supports a two-level hierarchical routing scheme through the use of OSPF areas. Each area consists of a set of subnets interconnected by routers. Routers attached to two or more areas are called area border routers (ABRs). OSPF ABRs can be configured to aggregate the subnet addresses in their areas, and to advertize these aggregates in the remainder of the network instead of individual subnet addresses. Consequently, address aggregation within OSPF areas results in a significant reduction in routing table sizes, smaller link-state databases and less network traffic to synchronize the router link-state databases.