[tor-talk] can't get tor to work :(

[Roger Dingledine]

On Sun, Mar 06, 2011 at 10:09:49AM -0800, Robert Ransom wrote:
> > In the default mode, it will hang on "connecting to a relay directory
> > failed (no route to host)"
> 
> All of the directory authorities crashed between 2011-03-06T10:00 and
> 2011-03-06T11:00 UTC.  Newly started Tor clients will not work until
> the directory authorities are running again.

There was indeed a directory authority outage, but it's unclear whether
the original bug report here is related to the outage.

When all directory authorities are down, new Tor clients can't bootstrap
if they don't have cached directory information from earlier that day. But
Tor clients that are already up and have directory information are all
set for about 24 hours. At that point, if the directory authorities
still haven't produced any new consensus about the network, things go bad.
Fortunately, in this case things didn't come to that.

We don't believe directory information that's too old, to protect clients
from attackers who choose their favorite consensus from the past year and
give that to their target client, either to skew their path selection
onto relays that the attacker controls, or to make the client build
paths in a distinguishable way from all the other clients. See
http://freehaven.net/anonbib/#danezis-pet2008
for a variation on this issue.

The reason I say it's unclear whether the original bug report is related
is that a Tor bridge should have been able to bootstrap the user the
whole time. Most Tor clients probably didn't notice any disruption.

For those wondering about the role of the directory authorities, see e.g.
https://www.torproject.org/docs/faq#KeyManagement

The bug in this case was that we had implemented partial IPv6 support
for Tor but hadn't implemented it in a consistent way. So when somebody
tried adding the experimental IPv6 support to his exit policy, the
directory authorities triggered an assert. We figured out the problem,
created a patch, and got a threshold of directory authorities to upgrade,
in about 8 hours. Plenty of time to spare. ;)

Mike opened this trac ticket afterwards so we can adapt our process for
handling these situations:
https://trac.torproject.org/projects/tor/ticket/2664

--Roger