How do you convert bandwidth to link cost for Cisco switches?

-This is the bandwidth to cost conversion. but i want to know exactly how to do it.

Bandwidth Cost

===================

4 Mbit/s 250

10 Mbit/s 100

16 Mbit/s 62

45 Mbit/s 39

100 Mbit/s 19

155 Mbit/s 14

200 Mbit/s 12

622 Mbit/s 6

1 Gbit/s 4

2 Gbit/s 3

10 Gbit/s 2

20 Gbit/s 1



Thanks for your helpThose are the default spanning tree port cost values, not OSPF cost numbers.



For spanning tree cost calculation, it's actually not standardized. Those values come from the IEEE's 802.1D specification, which gives recommended values for switch vendors to follow but does not define a formula to use.OSPF Comoputes the cost by using this formula: COST = Reference Bandwith / Link BW ( in Mbps )



By default, Reference BW = 100Mbps



You can change the reference bandwidth by going into the router ospf process and issuing the "auto-cost reference-bandwidth <new reference bandwidth in mbps>"



The Bandwidth cost you specified above, means that the Reference bandwidth has been change from the default 100Mbps to 4000Mbps, using these series of commands:



router ospf <process number>

auto-cost reference-bandwith 4000

exit



Hope that helps :)