BGP Route Issues

Randy randy_94108 at
Mon Aug 19 03:51:16 UTC 2013

11 prepends is beyond-excessive besides being annoying.
filter please _([0-9]+) _/1_/1_/1_

> From: Blake Dunlap <ikiris at>
>To: Christopher Karel <chris.karel at> 
>Cc: "nanog at" <nanog at> 
>Sent: Sunday, August 18, 2013 7:42 PM
>Subject: Re: BGP Route Issues
>Local Pref (which is common by the way to be set so customers > peers >
>transit). AS Path doesn't beat it.
>You can only request people follow the routes you want ingress, there's
>nothing you can do to force them to take a path to you short of
>deaggregation, and that only works until they notice it, and it irratates
>the rest of the world as well by using additional route slots.
>Poor routing is purely a viewpoint problem, not necessarily in agreement
>between all parties.
>On Sun, Aug 18, 2013 at 8:33 PM, Christopher Karel <chris.karel at>wrote:
>>   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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