Two links to same ISP

Unanswered Question
Oct 3rd, 2010

Hello Dear Experts,

    I have a question about the BGP redundancy link to two links to same ISP.

We are the transit to our customers. One of our customer has to connected to our Europe link. This customer also has

other link to other ISP to Europe link. The europe links connected to same ISP (TTK). Customer wants to do redundant

these two links. But the bgp with this customer and us is always up when our europe link has down. We have announced

default to customer by default originate command. We got the full table from TTK. When TTK link is down customer didn't

know about it. I think they used localprefence to our link.

  How to decide this issue? Please any idea about this?

   Thank you



I have this problem too.
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Mahesh Gohil Sun, 10/03/2010 - 17:58

Hi Bayanmunkh,

Your requirement here is stop advertising of default route to customer when your europe link goes down.

Now question to you. ....along with full routing table do you have accepted default route from TTK, If so instead of using default originate you can use

route-map to advt. default route to customer


ip prefix-list default permit

route-map DEFAULT-OUT permit 10
match ip address prefix-list default

router bgp xxxx

neighbor X.X.X.Y  route-map DEFAULT-OUT  out

This will remove default from customer bgp table once your europe link goes down.



bayanmunkh Sun, 10/03/2010 - 20:57

Dear Mahesh Gohil,

     Thanks a lot for your reply. It is very  helpful answer. But we got only full bgo table from europe not included  default. Also we got from other
  router that facing to USA.  Here:
               Routing entry for
               Known via "ospf gemnet", distance 110, metric 10, candidate default path, type extern 2
                Installed Sep 26 08:07:33.784 for 1w1d
               Routing Descriptor Blocks
    , from, via GigabitEthernet0/0/0/0
               Route metric is 10
               No advertising protos.
And we set the weights to routes from europe higher that internal  reason. I understand that we need to Full table+default from europe now?  Is this
cause any problem that two default routes on same router. Do we need anything else?

   Thank you very much


Mahesh Gohil Sun, 10/03/2010 - 21:31

Hi Bayanmunkh,

Another way is to put default route toward your europe peering and redistribute same to your bgp by "redistribute static route-map"

in global bgp while keeping default route-map with your customer bgp.

otherwise it is not possible to inform your customer to widraw default route if your peering goes down.

ultimately you need to relate your default route to that of peering by any means.




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