Unanswered Question
Jul 6th, 2009
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I have a 6509 with two paths to the same place with the same metric, I don't want to load balance due to the type of wan accelerator that I am using. Can anyone tell me how the path is then chosen? and how often it changes or why?

such as does the route table update take place due to another route change, is there a timeout that causes the route to change automatically (round robin).

I know how to fix the problem, but would like to know the timeouts/parameters on this for future reference.

Thanks, to anyone that can help.

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Jon Marshall Mon, 07/06/2009 - 09:44
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Not sure i fully understand the question.

If you have 2 equal cost routes then

1) If the load balancing is per packet then the router will switch between the 2 paths each time it sends a packet

2) If the load balancing is per destination then the router will switch between the 2 paths for each different destination IP address

If i have misunderstood the question please elaborate.


specialed351 Mon, 07/06/2009 - 10:03
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I don't have load balancing enabled and do not want to.

router eigrp x

maximum-paths 1

what I am asking is how eigrp decides which route it puts in to the table. why and when it switches



Joseph W. Doherty Mon, 07/06/2009 - 10:07
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"Can anyone tell me how the path is then chosen? and how often it changes or why? "

Believe that depends on the routing switching technology. For instance, route-cache vs. CEF. For the former, I think new destinations flows are just round-robined, but once destination is cached, same path is used until cache expiration. For the latter, there are different hash algorithms (somewhat like Etherchannel), and path is always deterministic. See http://www.cisco.com/en/US/tech/tk827/tk831/technologies_white_paper09186a00800a62d9.shtml and http://www.cisco.com/en/US/tech/tk827/tk831/technologies_tech_note09186a0080094806.shtml (NB: rules might be a bit different for a 6500)


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