The Cisco IOS `bandwidth kbps` interface-configuration command sets an interface’s configured bandwidth in kilobits per second. The value is used for calculations; it does not change the interface’s operating speed. section 18.1.3
Use the command carefully because the configured value can influence several mechanisms:
- OSPF calculates link cost from reference bandwidth divided by interface bandwidth. section 18.1.3
- Changing bandwidth can also affect EIGRP metrics and QoS mechanisms. section 18.1.3
- Use `ip ospf cost cost` instead when you want to change only a link’s OSPF cost. section 18.1.3
- Use the `speed` command when you need to change how fast the interface operates. section 18.1.3
OSPF cost scenario
With a 100 Mbps reference bandwidth, lowering an interface’s configured bandwidth raises its calculated OSPF cost; values below 1 are assigned a cost of 1. Verify resulting costs with `show ip ospf interface brief`. section 18.5
