Level3 (3356/3549) changes routing policy

Fredy Kuenzler kuenzler at init7.net
Thu Aug 2 08:33:38 UTC 2012

 From my observation Level3 has recently changed their routing policy. It 
seems that 3356 always prefers customer prefixes of 3549, regardless of the 
AS path length. Example (seen from 3356):


is preferred over


Considering that both 2914 and 3549 are peers of 3356, and 13030 is a 
customer of 3549, 3356 seems to give higher local-pref on the longer 
AS-path, likely to increase traffic and revenue of their sister network 3549.

Certainly it's common practice to overrule the BGP4 default behaviour, and 
widely used by smaller networks.

Still I'm surprised that it happened obviously rather undetected, at least, 
to my knowledge, Level3 did implement it silently and hasn't published an 
official statement or customer announcement, which I think, would have been 
fair, at least.

Considering that Level3 3356 and 3549 are by far the largest networks 
globally this decision must have a large impact on traffic flows and, of 
course money flows.

Maybe the BGP monitoring experts (aka Renesys et al) can shed some light?

Fredy Künzler
Init7 / AS13030

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