RIR filtering & Level3

Paul Stewart pstewart at nexicomgroup.net
Thu Nov 15 02:52:05 UTC 2007

We're getting 231740 routes from Level(3) at this moment.... hit me
offline with some specific prefixes and I'd be happy to share what we

Paul Stewart
Senior Network Administrator
5 King St. E., Millbrook, ON, LOA 1GO
Phone: 705-932-4127
Web: http://www.nexicom.net
Nexicom - Connected. Naturally.

-----Original Message-----
From: owner-nanog at merit.edu [mailto:owner-nanog at merit.edu] On Behalf Of
Justin Shore
Sent: Wednesday, November 14, 2007 9:43 PM
To: nanog at merit.edu
Subject: RIR filtering & Level3

Are any other L3 customers seeing the large number of /25 and smaller 
routes from L3?  I'm seeing almost 2500 of these routes in 4/8, some but

not as many in 8/8 and still more in L3's non-US allocations.  Looking 
at the AS paths for a handful of those specific networks I only see them

via our L3 connection and not via our other 2 upstreams.  I'm seeing 
paths to the larger aggregate networks via our other upstreams of 
course; the Oregon and AT&T route servers see the same aggregates too. 
To be more accurate we actually touch L3's acquisition form a year or so

ago, Telcove (19094).  All of the small routes are originating from L3 
though (3356).

Best I can tell L3 is aggregating before it advertises to a peer but not

before it advertises to a customer.  Or, on the otherhand, perhaps L3 is

advertising without aggregation to Telcove and Telcove is not 
aggregating before advertising to us.

So, that said, what is everyone else doing to perform sanity checks on 
their learned routes?  Are a good many implementing RIR filtering and 
dropping everything smaller than a /24?  L3 of course isn't the only 
source of these tiny routes but it's so obvious I saw it and wasn't even

looking for it.  This would explain why I'm getting so many more routes 
from L3 too.  I'm getting 232k from AT&T, 233.5k from Cox and 244k from




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