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OSPF auto-cost

what is difference between "ospf auto-cost reference-bandwidth" and "auto cost reference-bandwidth" syntex?

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Re: OSPF auto-cost

There is no difference between the commands. Both are used to tune the reference bandwidth used by OSPF for calculating the link cost (metric)

In Cisco IOS Release 10.3 and later releases, by default OSPF will calculate the OSPF metric for an interface according to the bandwidth of the interface. For example, a 64K link will get a metric of 1562, and a T1 link will have a metric of 64.

The OSPF metric is calculated as the ref-bw value divided by the bandwidth, with mbps equal to 108 by default, and bandwidth determined by the bandwidth (interface) command. The calculation gives FDDI a metric of 1.

If you have multiple links with high bandwidth (such as FDDI or ATM), you might want to use a larger number to differentiate the cost on those links.

The value set by the ip ospf cost command overrides the cost resulting from the auto-cost command.

HTH, rate if it does

Narayan

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