[tor-talk] Identifying use of relay as an Entry node

[Roger Dingledine]

On Thu, Jun 09, 2011 at 06:08:05PM +0200, tagnaq wrote:
> > How can I tell when said relay (to which I have full access)
> > is being used as an entry node by other clients on the net
> > (those not under my control) ?
> > 
> > Or put another way, were said relay to be instrumented,
> > would such identification be possible?
> 
> If someone connecting to your ORPort isn't a relay in the consensus it
> is probably a client or a bridge.
> In rare cases it might even be a relay. (IP address in descriptor
> differs with current outbound IP address)

You can look at the identity key that the connection presents -- if it's
a relay, it will present its identity key, even if it's coming from a
different IP address than is in its descriptor.

But I didn't understand the original question. Are you asking if relays
can enumerate the clients that use them for their first hop? If so, yes.
See also point f on https://www.torproject.org/download/download#warning

--Roger