Hierarchical Network Design Techniques

When designing your OSPF network, the following factors are supported by OSPF and are currently accepted network design theories:

• A three-tiered backbone approach allows fast convergence and economy of scale.

• Never use more than six router hops from source to destination (see the following note).

• Use 30 to 100 routers per area. (This can be adjusted depending on factors discussed later.)

• Do not allow more than two areas per Area Border Router (ABR) in addition to the ABR's connection to area 0. Otherwise, the ABR must keep track of too many linkstate databases.

NOTE The Cisco Systems network recommends that you have no more than six hops from source to destination when designing a hierarchical enterprise network. This has some validity; however, in practice, the number of hops you can see depends on what a network is trying to accomplish. Large, long-haul international networks by nature have more than six hops.

72 Chapter 2: Introduction to OSPF

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