auto-cost reference-bandwidth (OSPFv2)

Configures reference bandwidth.

Syntax

auto-cost reference-bandwidth { value | use-active-ports }

no auto-cost reference-bandwidth

Command Default

Reference bandwidth is 100 Mbps.

Parameters

value: Reference bandwidth in Mbps. Valid values range from 1 through 4294967.
use-active-ports: Specifies that any dynamic change in bandwidth immediately affects the cost of OSPF routes. This parameter enables cost calculation for currently active ports only.

Modes

OSPF router configuration mode

OSPF router VRF configuration mode

Usage Guidelines

Use this command to configure the cost of an interface that a device advertises to it's OSPF neighbors. OSPF calculates the cost of a route as the ratio of the reference bandwidth to the bandwidth of the egress interface. An increase in the reference bandwidth results in an increased cost. If the resulting cost is less than 1, the software rounds the cost up to 1.

The bandwidth for interfaces that consist of more than one physical port is calculated as follows:

LAG group — The combined bandwidth of all the ports.
Virtual interface — The lowest individual bandwidth of all the ports that carry the VLAN for the associated VE.

If a change to the reference bandwidth results in a cost change to an interface, the device sends a link-state update to update the costs of interfaces advertised by the device.

Note

If you specify the cost for an individual interface (by using the ip ospf cost command), the cost you specify overrides the cost calculated by the software.

The no form of the command disables bandwidth configuration.

Examples

The following example configures a reference bandwidth of 500.

device# configure terminal
device(config)# router ospf
device(config-router-ospf-vrf-default-vrf)# auto-cost reference-bandwidth 500

The reference bandwidth specified in this example results in the following costs:

10 Mbps port‘s cost = 500/10 = 50.
100 Mbps port‘s cost = 500/100 = 5.
1000 Mbps port‘s cost = 500/1000 = 0.5, which is rounded up to 1.

The costs for 10 Mbps and 100 Mbps ports change as a result of the changed reference bandwidth. Costs for higher-speed interfaces remain the same.