Configuring OSPF | OSPF Overview |
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Classification of Routers
When an AS is split into OSPF areas, the routers are further divided according to function into the follow- ing four overlapping categories:
•Internal routers. A router with all directly connected networks belonging to the same area. These routers run a single copy of the SPF algorithm.
•Area border routers. A router that attaches to multiple areas. Area border routers run multiple copies of the SPF algorithm, one copy for each attached area. Area border routers condense the topological information of their attached areas for flooding to other areas.
•Backbone routers. A router that has an interface to the backbone. This includes all routers that inter- face to more than one area (i.e., area border routers). However, backbone routers do not have to be area border routers. Routers with all interfaces connected to the backbone are considered to be internal rout- ers.
•AS boundary routers. A router that exchanges routing information with routers belonging to other Autonomous Systems. Such a router has AS external routes that are advertised throughout the Autono- mous System. The path to each AS boundary router is known by every router in the AS. This classifi- cation is completely independent of the previous classifications (i.e., internal, area border, and backbone routers). AS boundary routers may be internal or area border routers, and may or may not participate in the backbone.
OmniSwitch 6600 Family Advanced Routing Configuration Guide March 2005 | page |