[tor-relays] Connectivity issues; disabling my relay

[Steven Chamberlain]

Hello!

My non-exit Tor relay "4pyro2eu3org0" in the United Kingdom is served by
a consumer FTTC broadband line.  It had a rare, unexplained outage on
2016-01-19 between 00:00 and 02:00 UTC.  Two other lines with the same
provider, terminating in the same local telephone exchange, were
unaffected.

When it came back, latency was different (lower) than before, to the
first hop (the LNS in Birmingham) suggesting ATM traffic maybe taking a
different (faster) route through BT's network *or* just my modem having
resynced with different modulation.  (Smokeping graph attached).

But what concerns me, are intermittent bursts of packet loss (for about
3 seconds, happening every 10-60 seconds) which have been happening for
more than 24 hours since.

My ISP has checked with BT and assures me no maintenance work was
scheduled that night;  they see in their logs that my PPP session
dropped at that time but believe no other customers at my local
telephone exchange were affected.

I consider that - whatever may be causing this - this kind of
interruption to Tor relay traffic, could make timing attacks easier for
an observer.  So I'm shutting down my relay until this can be explained
and fixed.

At the very least, I should replace the BT Openreach-supplied VDSL modem
(Huawei HG521) or its firmware with something I have more control over
(and third parties have less control over...)

Here's how the issue looks in mtr (at 1-second intervals);  it affects
all IP traffic.  Maybe this is something benign, but I encourage other
relay operators to be vigilant nonetheless.

 1. 217.155.40.118 (Tor relay)
...................................................................................
 2. 62.3.80.17 (LNS)
.........................???......................???............???...............  
 3. x.x.x.x (test machine on same ISP)
.........................???......................???............???...............  

and in reverse:

 1. x.x.x.x (test machine on same ISP)
...................................................................................
 2. 62.3.80.17 (LNS)
...................................................................................  
 3. 217.155.40.118 (Tor relay)
.........................???......................???............???...............

Regards,
-- 
Steven Chamberlain
steven at pyro.eu.org
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