AS path question.

Justin M. Streiner streiner at
Wed Nov 10 14:31:44 CST 2010

On Wed, 10 Nov 2010, Greg Whynott wrote:

> when I looked at the logs I was a bit confused at what i was looking 
> at...   why is it there are multiple AS's in the path that appear to be 
> the same AS?  I expected an AS path comprised of mostly unique ASs.
> instead of this:
> 476330: Nov 10 14:55:07.247 EDT: %BGP-6-ASPATH: Long AS path 549 26677 
> 6939 21011 43022 43022 43022 43022 43022 47359 47359 47359 47359 47359 
> 47359 47359 47359 received from isp router: More than configured 

The originator of this route, and to a lesser extent, their upstream 
provider are prepending the hell out it, and that's why your router 
doesn't like it.  AS path prepending has its uses, but prepending the 
origin AS 7x is not likely to make much of an impact from a traffic 
engineering perspective, and only serve to make the AS path unnecessarily 


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