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magnavox
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How to set routing filter to change cost/metric?

Wed May 04, 2016 9:07 pm

I need to change metric/cost in "OSPF out" for single routes
matching some attribute (like distance).

Exist any way to make this by Routing filters?

Best regards.
 
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ZeroByte
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Re: How to set routing filter to change cost/metric?

Tue Jun 14, 2016 7:08 pm

I need to change metric/cost in "OSPF out" for single routes
matching some attribute (like distance).

Exist any way to make this by Routing filters?
Link-state routing protocols aren't designed to work this way. They're designed to create a map of the network, and figure out the shortest way to reach the various parts of it, and keep a list of what networks are connected to which parts of it. In this design, if link P->Q is the best way to get to router Q, then it follows that anything connected to Q should be reached via P->Q.

Policy routing of the sort you're asking about is more of a BGP thing, and BGP isn't a good protocol to use as an IGP.

The most you can do is balance multiple links with equal cost multipath (ECMP). You could try putting a static route for the "exception" traffic but that's a klunky workaround that's likely to have unforeseen side effects down the road. The best thing to do is follow best practices and design your network with the behavior of OSPF in mind, instead of trying to bend OSPF into a shape that it was never meant to hold. It's like Feng Shui for networking. :)

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