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Routing & Switching · Foundational

Reference Bandwidth

The bandwidth value OSPF divides by interface bandwidth to calculate cost, 100 Mbps by default.

Definition

Raising the reference bandwidth lets OSPF distinguish between 1, 10 and 100 Gbps links. It should be set identically on all routers in the domain to keep costs consistent. On Cisco the command is auto-cost reference-bandwidth in Mbps.

Example

auto-cost reference-bandwidth 100000 sets 100 Gbps as cost 1.

Exam tip

Changing it on only some routers causes inconsistent, asymmetric path selection.

Related terms