Page 392

Redistribution of Routing Protocols

357

Be is the bandwidth capacity. This is the capacity without any traffic.

Dc is the delay associated with the link to the next hop in the path to
the network.

r is the reliability of the physical link. If a circuit has several outages,
this is calculated into the composite metric.

Just as with IGRP, you can set these metrics manually from within the

Configuration mode. Details on how to change metrics will be explained
after we discuss how EIGRP is configured.

OSPF

The metrics associated with OSPF are different from those associated with
IGRP and EIGRP. OSPF uses bandwidth as the main metric in selecting a
route. The cost is calculated by using the bandwidth for the link. The equa-
tion is 100,000 divided by the bandwidth. You may change bandwidth on
the individual interface.

The cost is manipulated by changing the value to a number within the

range of 1 to 65,535. Because the cost is assigned to each link, the value must
be changed on each interface. The command to do this follows:

ip ospf cost

Cisco bases link cost on bandwidth. Other vendors may use other metrics to

calculate the link's cost. When connecting links between routers from differ-

ent vendors, you may have to adjust the cost to match the other router. Both

routers must assign the same cost to the link for OSPF to work.

You can configure the OSPF distance with the following command:

distance ospf [external | Intra-area | Inter-area]
distance

This command allows the distance metric to be defined for external OSPF,

and intra-area and inter-area routes. (Intra-area and inter-area routes are
discussed in the "Configuring OSPF" subsection.) Distance values range
from 1 to 255--and the lower the distance, the better.

Other values important to OSPF's operation are not actually metrics, but

can be configured as well. Values such as the router ID and router priority

www.sybex.com