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Level3 (3356/3549) changes routing policy
From: Fredy Kuenzler <kuenzler () init7 net>
Date: Thu, 02 Aug 2012 10:33:38 +0200

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 K├╝nzler
Init7 / AS13030

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