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OSPF External Route Metrics Types explanation

This article describes the OSPF redistribution routes related to the route metrics types.

Scope

FortiGate.

Solution

Type 1

Considered close to the AS.

Metric is based on the sum of the internal and external costs.

Type 2

Considered far away from the AS.

Metric is based on the external cost only.

OSPF router prefers a type 1 external router over a type 2.

Each external route is assigned a metric. There are two types of external-route metrics.

A type 1 metric is the sum of the external cost plus the internal cost to reach the ASBR. A type 2 metric is only the external cost (the internal cost is not considered).

If there are two external routes to the same destination, one type 1 and one type 2, an OSPF router selects the type 1 route over the type 2 route. That is represented in E1 and E2.