OFPF Cost Tuning
Share this page:NLRI - Network Layer Reachability Information
OSPF routes are mainly classified based on their metric, where the Metric and Cost are calculated based only on the Link Bandwidth.
Cost = 100/(BW[Mbps])
There are two things you could play with here:
1. Set the REFERENCE BW (because with the formula above the Max cost value is 1, and we dont want the same values for 100M and 10G link)
** (config-router)#auto-cost reference-bandwidth 10000**
*10000 is 10000 Mbps
* Dont forget to clear the OSPF process in order for the changes to take effect:
** #clear ip ospf process**
2. Change the COST in the Interface Configuration
** (config-if)#ip ospf cost 20**
and check the result:
** Cisqueros_R1#show ip ospf inter Lo0 | i Cost **
** Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 20**
Then check the metric on the OSPF Neighbor:
Cisqueros_R2#show ip route 1.0.0.0
Routing entry for 1.0.0.0/8
** Known via “ospf 1”, distance 110, metric 84, type intra area <— METRIC 84**
** Last update from 10.1.12.1 on Serial1/0.21, 00:02:31 ago**
** Routing Descriptor Blocks:**
** * 10.1.12.1, from 1.1.1.1, 00:02:31 ago, via Serial1/0.21**
** Route metric is 84, traffic share count is 1**
Metric is 84, which is the cost of the Serial interface between routers 1 and 2, and the Cost of the Loopback0 interface on Router 1.
Default cost of the Loopback interface is 1, so it actually increased for 20-1 = 19