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New Member

OSPF external routes

An OSPF multiarea structure has some ASBRs configured to propagate E1 and E2 external routes from different external ASs. What type of external routes has priority in an internal OSPF router when:

* E1 cost > E2 cost (to the same destination)

* E2 cost > E1 cost (to the same destination)

* E1 cost = E2 cost (to the same destination)

Please comment.

3 REPLIES
New Member

Re: OSPF external routes

The cost of a E2 route is the external cost .

A E1 cost is the addition of the external cost and the internal cost used to reach that route. A E1 route is always preferred over a E2 route for the same destination. Hope it will help.

rgds

New Member

Re: OSPF external routes

Hi Ahmed:

Only to be absolutely clear, the E1 route is always preferred over a E2 route, independently of the advertised cost ?? It happens that we have found contradictory statements in some Cisco Press Books (ACRC, DCN, BSCN).

thanks in advanced.

Re: OSPF external routes

"Type 1 external paths are always preferred over type 2 external paths." - RFC 2328.

Whenever in doubt, always consult the RFC's. Never rely solely on Ciscopress.

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