7.2 OSPF Route Summarization

CCNP RS 300-101, Optimizing OSPF Behavior, Uncategorized

There are two focal objectives for summarization in ANY routing protocol:

  1. Reduce the size of the routing table
  2. Reduce the number of routing update messages

Therefore, the purpose of route summarization is to maintain connectivity with fewer routing entries, thereby decreasing overhead.

****

Route summarization is the key to scalability in OSPF.

In OSPF, there are two summarization points to consider:

  • At the ABR, summarizing Type 3 (summary) LSAs
  • At the ASBR, summarizing Type 5 (external) LSAs

Route summarization requires a good addressing plan using proper VLSM design. Networks should be assigned contiguously.

Route summarization can create sub-optimal routing if many ABRs or ASBRs exist in an environment.

Published