Strange Reachability Issue

Brandt, Ralph ralph.brandt at
Tue Sep 4 13:18:49 UTC 2012

I will bet that will bet that within 48 hours of you checking and
posting this the problem will mysteriously go away. 

Ralph Brandt
Mechanicsburg PA 17055

-----Original Message-----
From: Bryn Sadler [mailto:bryn.sadler at] 
Sent: Tuesday, September 04, 2012 9:02 AM
To: nanog at
Subject: Strange Reachability Issue

Hello all,

I was wondering if anyone might be able to share their thoughts on a
strange issue we're experiencing with NTT at the moment. We're AS48273
and are advertising a prefix through AS 8190 (single
upstream provider at the moment). We've been doing this for some years
now, and all has been fine. The last few days we seem to have
disappeared from NTT's worldwide routing tables, with the exception of
Europe. If we use their looking glass to query any NTT european router
we can see the prefix, being learned via AS 286 then AS 8190, as
expected. If we look at any other router outside of europe, there is
simply no entry for that prefix. Elsewhere in the world we seem to be
fine, we're in every other network I've looked at and general
reachability is fine.

First step was to contact the NTT NOC, and they've confirmed that
there's no Internal routing/config issue on their network, but that they
cannot discuss their peering arrangements due to NDAs. We've also picked
it up with KPN (AS 286), who have verified that the prefix is visible
throughout their network (true), and that they are advertising it to
NTT. One thing of note is that Global Crossing are learning our prefix
from KPN as well, and the prefix is showing fine in their global tables.

We seem to be caught in the classic finger pointing scenario, but I
can't get my head around why the prefix is visible in NTT Europe, but
not anywhere else, unless they have a config error somewhere on their
network. We've checked a few of the routes from AS 8190 and they are in
the NTT global tables just fine, and at least in Europe they seem to
have the same community values etc. We're still following on with NTT,
but can anyone offer some wisdom for new avenues to pursue?

Thanks for your help,

Bryn Sadler

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