sundar.palaniappan Fri, 04/04/2008 - 07:35
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Q. How does OSPF calculate its metric or cost?

A. OSPF uses a reference bandwidth of 100 Mbps for cost calculation. The formula to calculate the cost is reference bandwidth divided by interface bandwidth. For example, in the case of Ethernet, it is 100 Mbps / 10 Mbps = 10.

Note: If ip ospf cost cost is used on the interface, it overrides this formulated cost.




Joseph W. Doherty Fri, 04/04/2008 - 16:53
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An additional note

Cisco behaves as Sundar's notes, but OSPF cost is not defined as such by the standard. Other brand equipment either does not auto cost on link banwidth, or uses a different base metric. (NB: There's a command to adjust the auto cost base OSPF bandwidth metric on Cisco.)


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