Default routing costs Homogeneous Networks

In a homogeneous network, all the transmission facilities are the same. All the LAN interfaces would be 10-Mbps Ethernet, for example, and all the serial WAN interfaces would be T1s. In such a scenario, using the default values would not likely cause routing problems. This would be particularly true if there were little, if any, route redundancy.

To illustrate this point, consider the network diagram in Figure 12-10.

Figure 12-10: Acceptable use of OSPF's default interface values.

Figure 12-10: Acceptable use of OSPF's default interface values.

In Figure 12-10, a default value of 1,768 was assigned to each of the interfaces. All the WAN links, however, are T1s. Given that they are all the same, it doesn't matter whether the value assigned them is 1, 128, 1,768, or 1,000,000! Routing decisions, in a homogeneous network, become a simple matter of counting and comparing hops (albeit in multiples of the interface costs). This would be true regardless of how much, or how little, route redundancy existed in the network.

Obviously, in a complex network with substantial route redundancy and a disparity in the actual transmission technologies used, the default value would not enable selection of optimal routes to any given destination.

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