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List:       isp-bgp
Subject:    [isp-bgp] BGP and bad routes down the line
From:       Andy <browna () interv8 ! co ! uk>
Date:       2003-12-18 11:09:43
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Hi All,

Have an interesting problem reering its head, and at the moment we don't have 
a good solution.

cisco 7206VXR router connection to two ISPs, one 16Mb link and one 10Mb link.
the 16Mb is preferred by as-prepends.

If ISP1 (16Mb link) has a routing error like this:
1   <10 ms   <10 ms   <10 ms  192.168.10.15
  2   <10 ms   <10 ms   <10 ms  CORE-ROUTER
  3    16 ms    15 ms    16 ms  1.1.1.1
  4    16 ms    16 ms    15 ms  1.1.1.2
  5    16 ms    16 ms    15 ms  1.1.1.1
  6    47 ms    16 ms    15 ms  1.1.1.2

(IP's hidden to protect the guilty! but as you can see 1.1.1.1 and 1.1.1.2 are 
in a loop)

How can our router understand this and route traffice down the other link??
The trick is that not ALL routes on 1.1.1.1 / 1.1.1.2 are going in circles, 
some are fine others aren't. Isn't this the point of BGP or am I missing 
something totally obvious??

Our boss pulled the link to ISP1 out until they fix the faulty router, which 
obviously has temporarily fixed the problem, but not a clever fix!

Any help would be very kind :)

Andy.



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