Level3 (3356/3549) changes routing policy

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?

Hi Fredy,

Level 3 owns both 3356 and 3549.
They're simply preferring to have their customers pay them, rather than
a 3rd party.

I don't think it's suprising at all that they're doing it. If, as you
think, it's only happened recently then what is suprising is that it
didn't happen sooner IMO.


I would also guess that over time, 3549 will go away, as the GX network gets borged into Level3.


It probably should be noted that AS3356's local pref heirarchy is as follows:

Highest: customers of 3356
Next highest: customers of 3549
Lowest: peers

This does not really seem odd at all, and is probably what I would do if I owned two separate networks that were going to take a long time to merge... We noticed this change at least three months ago so it is not a super recent change.

Thanks David, you hit the nail on the head on both points.

Level 3 made the routing policy change last November, roughly 6 weeks after the acquisition of Global Crossing.


Better to use communities instead.