OSPF Issue

Unanswered Question
Jun 11th, 2009
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Hi,


Have 3 sites connected to each other

Site#A -----connected----Site#B ( 2MB )

Site#A------Connected----Site#C ( 2MB )

Site#B------Connected----Site#C ( 2MB )


All running OSPF, but traffic from Site#B to Site#C goes via Site#A instead going directly since they have connection.


Have noticed that connection from Site#B to Site#C has more hops in between.


Is it possible to force Site#B to send all traffic for Site#C directly.



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paul.matthews Thu, 06/11/2009 - 02:04
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This looks a little odd - with all routers in the same area, and all interface settings at default, I would expect traffic to go directly from B to C.


This implies that either you have areas set up, you have adjusted costs on one or more links or you have a problem with the link from B to C.


Is CDP enabled? Can you see the router at C from the router at B (And vice versa)? Does the router at B show up when you do "sh ip ospf nei"? What about the other way? Can the routers at B&C ping each other?


If you could add the outputs of:

sh ip ospf nei

sh ip ospf int (Just for the interfaces that link B&C)

sh int (Just for the interfaces that link B&C)

sh cdp nei

sh ip prot


we may be able to help more.

Richard Burts Thu, 06/11/2009 - 03:55
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Paul


When I first read the original post I assumed that the environment was three routers (A, B, and C) which also seems to be an assumption that you are making. But as I read more carefully I noticed this:

Have noticed that connection from Site#B to Site#C has more hops in between

which pretty clearly indicates that there are more routers and a more complicated topology that we thought.


I agree that we need more information about the environment before we can adequately understand the issue and find a solution.


HTH


Rick

paul.matthews Thu, 06/11/2009 - 04:44
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Indeed - My understanding of the "more hops" comment was reading that as the extra hop being site B - I suspect the original poster is not a native english speaker, so we may need to be careful about interpretations.


A full diagram would help, with clarity of how direct connections are.


Paul.

ronald.ramzy Fri, 06/12/2009 - 09:12
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When I do traceroute from Site#B to Site#C it takes 9 hops.


thats the reason traffic initaiting from Site#B to Site#C passing via Site#A


How can I force traffic to move from Site#B to Site#C



Richard Burts Fri, 06/12/2009 - 18:51
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Ronald


From an initial description of 3 sites arranged in a triangle to a situation where SiteB to SiteC is 9 hops is a pretty major switch.


Generally speaking, yes you can force traffic to move from SiteB to SiteC. But for us to make suggestions about how to do that we will need considerable more informaiton about the topology and about how the routers are configured.


HTH


Rick

paul.matthews Sun, 06/14/2009 - 23:20
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The only way I can reconcile your original post with 9 hops between two sitea that claim to be adjacent is that the 2M link is across an MPLS network with TTL propagation enabled.


As Rick says, we really need to know your complete topology to help.


The easy way to force traffic is with a static route, but without knowing the topology, that could just make things worse, causing a black hole due to a routing loop.

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