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Community Member

ospf summarisation

Hi,

How does an ABR generate the cost for ospf summarised routes..?

6 REPLIES
Hall of Fame Super Gold

Re: ospf summarisation

Ammavan

According to RFC 2328 when an ABR summarizes a range of routes it examines the routes to be summarized and advertises the highest cost of the individual routes.

HTH

Rick

Community Member

Re: ospf summarisation

Rick,

Thats a good answer.

Can a user anyway manipulate the cost of the summarised route,in this case..?

Thanks in advance,

Hall of Fame Super Gold

Re: ospf summarisation

Ammavan

Other than being able to use the ospf cost interface command to manipulate the metric of the individual routes (make some other route have a higher cost, or make the current highest cost lower) I am not aware of any way that you can manipulate the cost of the the summarized route.

HTH

Rick

Purple

Re: ospf summarisation

Rick/Ammavan,

My observation has been that IOS is not compliant with RFC2328 in this area. The metric used for the summarised routes by the ABR is the *lowest* of all the metrics of the routes being summarised.

Also, there *is* a way to manually set the summary for the summarised route using:

area range [advertise | not-advertise] [cost cost]]

Hope that helps - pls rate the post if it does.

Paresh

Purple

Re: ospf summarisation

Just another note: the cost keyword was added in IOS 12.2

Paresh

Hall of Fame Super Gold

Re: ospf summarisation

Paresh

Good observation.

Rick

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