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Compare OSPF E1 Vs E2

Unanswered Question
Nov 7th, 2006
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I know the different of E1(external cost + internal cost ) and E2 (external cost), but how can I choose what type of External route is the best to fit the network

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mheusinger Tue, 11/07/2006 - 23:55
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First, if there is only one ASBR (redistribution) router then it makes no difference - OSPF will have no choice. If there are two or more ASBRs then it makes a difference. In brief, E1 routes let you choose the "nearest" exit point, whereas E2 can be used for a primary/backup scenario.

Example: you have two internet connections in two locations and each internew gateway inserts a default route. If gateway A uses E2 with metric 20 and gateway B uses E2 with metric 30, all internet traffic will go through A. This means from site B internet traffic is going across your WAN to site A and then routed to the internet.

If this is not what youwant, you can use E1 routes with equal metric and each site will use the local internet gateway, because of the better metric and you still have redundancy.

Metric type and seed metric can be set during redistribution into OSPF.

Hope this helps! Please rate all posts.

Regards, Martin

jackyfung Wed, 11/08/2006 - 00:48
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Thanks ! Martin,

I think I just partially understand it. Is there any link that I can have deeply read it for such above situation.


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