D-Link DES-3326S manual Areas and Border Routers, 132

DES-3326S Layer 3 Fast Ethernet Switch User’s Guide

Router A
0
128.213.0.0	10
10
Router B	Router C
5	10

192.213.11.0222.211.10.0

Figure 5-21. Constructing a Shortest Path Tree - Completed

Note that this shortest path tree is only from the viewpoint of Router A. The cost of the link from Router B to Router A, for instance is not important to constructing Router A’s shortest path tree, but is very important when Router B is constructing its shortest path tree.

Note also that directly connected networks are reached at a cost of 0, while other networks are reached at the cost calculated in the shortest path tree.

Router A can now build its routing table using the network addresses and costs calculated in building the above shortest path tree.

Areas and Border Routers

OSPF link-state updates are forwarded to other routers by flooding to all routers on the network. OSPF uses the concept of areas to define where on the network routers that need to

132 Switch Management and Operating Concepts