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s the size of your networks grows, so does the size of your
route topology and routing tables. Unfortunately, this large amount of infor-
mation causes more CPU processes to occur and requires more physical
memory on the router. If something isn't done about the size of the collection
of information contained in the routing tables, your router will be advertis-
ing routing information that may be unnecessary to advertise.
Summarization provides an excellent way to reduce the size of the topol-
ogy and routing tables and significantly reduce the load on the router. Sum-
marization provides a way to aggregate routing information, summarize the
known routes, and reduce the lines in the IGP tables. If summarization
doesn't occur, every route--including those the router doesn't need to know
about--will be learned by the router and stored in the tables. This appendix
covers route summarization related to Open Shortest Path First (OSPF),
Enhanced Interior Gateway Routing Protocol (EIGRP), and Border Gateway
Protocol (BGP).
Route Summarization for OSPF
y implementing route summarization for OSPF, you help to elimi-
nate the number of Link State Advertisements that are sent when there is a
change in the topology of the network. When route summarization is applied
to OSPF, and when there are frequent changes in the router's topology, you
can eliminate the advertising of those changes, particularly in the backbone
(Area 0).
Copyright ©2001 SYBEX , Inc., Alameda, CA