OSPF Cost

camila9898 · ‎04-04-2008

What is the OSPF Cost inverse of the bandwidth or something else..

sundar.palaniappan · ‎04-04-2008

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.

OSPF FAQ:

http://www.cisco.com/warp/public/104/9.html

HTH

Sundar

Joseph W. Doherty · ‎04-04-2008

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.)