exit and guard flag

[Roger Dingledine]

On Mon, Jul 27, 2009 at 08:23:15PM +0200, Olaf Selke wrote:
> Hi there,
> 
> I can confirm Roger's theory that exit traffic drops when gaining the
> guard flag.
> 
> Olaf

Hi Olaf,

Mike Perry recently found two further reasons why this is the case.

The first (known) reason is that once you get the Guard flag, clients
assume you're not useful for the middle hop anymore, since now you
presumably have a lot of clients using you for the first hop. Once you've
had the Guard flag for a while, that's a reasonable assumption -- but
on day one, pretty much nobody has chosen you as their guard yet.

New reason #1 is that clients were picking guards without weighting
by bandwidth:
https://bugs.torproject.org/flyspray/index.php?do=details&id=1217
So fast guards would get just the same amount of attention as slow
guards. Tor 0.2.2.7-alpha resolves this, and 0.2.1.23 (whenever we put
it out) will too. So the load balancing here should slowly correct itself
over time.

New reason #2 is that in the special case where you have both the Guard
flag *and* the Exit flag, we aren't giving you as much attention as we
should have. See Mike Perry's recent or-dev post with details:
http://archives.seul.org/or/dev/Jan-2010/msg00012.html

There's a third reason lurking, which is that the directory authorities
seem to be making really bad decisions about which relays ought to get
the Guard flag. That one is still unsolved though. It looks like the
uptime and stability tracking is broken somehow.

This time for sure! :)
--Roger

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