BGP Route Issues

Christopher Karel chris.karel at
Mon Aug 19 01:33:39 UTC 2013

   Good evening,

     I'm hoping you guys might be able to offer some advice or insight 
into a BGP problem I've got.  I've noticed some strange routes between 
our network, AS27270, and AS22943.  It looks like both our networks are 
dual homed.  One ISP as the primary, and the other used as a backup, 
with path prepending to prevent it from actually being used except in an 
outage.  However, our route to 22943 appears to be using their backup 
link.  (27270 4323 7018 22943 22943 22943 22943 22943 22943 22943 22943 
22943 22943 22943)  Which is strange, because we can reach their primary 
ISP without any such rigmarole.

     Playing around with Looking Glass servers indicates that Cogent 
(AS174) has a similar backup route to our network.  (174 22402 27270 
27270 27270 27270 27270 27270)  Everywhere else I check seems perfectly 
sane.  But since Cogent is essentially in-between the two networks I'm 
troubleshooting, I would assume that the other network has a similar 
route.  But Cogent won't talk with me about this, since I'm not a customer.

     So as far as advice goes, is there a common issue that might result 
in such poor routes in both directions?  Any further troubleshooting 
that I should be doing?  Or any ideas on how to help remedy things that 
appear to be outside our network/ISP?  Or are we doing something so 
wrong that this is all my fault?

I'd really appreciate any input on this.

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