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Routing & Switching · Foundational

OSPF Cost

The OSPF interface metric, calculated as reference bandwidth divided by interface bandwidth, summed along a path.

Definition

Cisco's default reference bandwidth is 100 Mbps, so all links 100 Mbps and faster get cost 1 unless the reference is raised. Cost can be set directly with ip ospf cost or influenced by changing the bandwidth command. Junos also defaults to 100 Mbps reference and uses the metric statement.

Example

ip ospf cost 10 on Gi0/1

Exam tip

With default reference bandwidth, FastEthernet, Gigabit and 10-Gig links all cost 1; set auto-cost reference-bandwidth consistently on all routers.

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