Strange Reachability Issue

[Bryn Sadler <bryn.sadler () essensys co uk>]

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 94.198.184.0/21 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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