Re: [nsp] load sharing with OSPF external metrics

From: Roger Gottsponer (gottsponer@switch.ch)
Date: Fri Jan 09 1998 - 09:09:53 EST


Phil,

>This behaviour seems to contraduct anything I can find in
>the Cisco documentation.

First of all, I found an interesting passage in RFC 2187 (OSPF
Version 2):

   Processing of Type 2 external metrics is simpler. The AS
   boundary router advertising the smallest external metric
   is chosen, regardless of the internal distance to the AS
   boundary router.
   [...]
   When several equal-cost Type 2 routes exist, the internal
   distance to the advertising routers is used to break the tie.

So the behavior you experienced seems to be ok.

>into our OSPF. So he has multiple OSPF routes to our central
>core router, and these paths will have in general different
>OSPF path costs, and these costs will also change frequently
>as the network is grown. Therefore, I want to remove the
>OSPF path costs as a factor in the load sharing. I had
>thought I could do this by redistributing the customer's RIP
>routes with equal OSPF external-type 2 metrics at each POP.

If I understood you right, you would like to see your customer
connections with equal metric paths from each of your routers.
I think this makes no sense, because it would lead to some
nice routing loops. Traffic arriving at a router would be sent
on via the different paths, which means that a part of this
traffic would be sent back via the receiving path.

Regards,

Roger

BTW: something wrong with your return key??

Roger Gottsponer gottsponer@switch.ch
SWITCHlan +41 1 268'15'34



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