[tor-dev] Detecting multi-homed exit relays (was: Onion auto-redirects using Alt-Svc HTTP header)

grarpamp grarpamp at gmail.com
Sat Nov 18 23:08:11 UTC 2017

>> Detecting exit nodes is error prone, as you point out. Some exit nodes
>> have their traffic exit a different address than their listening
>> port. Hey does Exonerator handle these?
> Right.  It's not trivial for tor to figure out what exit relays are
> multi-homed -- at least not without actually establishing circuits and
> fetching content over each exit relay.
> I just finished an exitmap scan and found 17
> exit relays that exit from
> an IP address that is different from what's listed in the consensus:

This mode of operation, regardless of how it happens, is not in
itself a problem, nor cause for alarm. In fact, the nature of these
"exit IP different than ORPort" relays can and often does assist
users in circumventing censorship... a fundamental use case of Tor.
For instance, the arbitrary automated and blind blocking via dumb
blocklists that prevent even such most basic user activity and human
right to knowledge as simply reading websites via Tor. Such blocking
examples can often be found here:

It's also entirely up to the exit operator to determine if the
third party non contractual / SLA exonerator service is of any
particular use or benefit to them or not... perhaps they have other
notary means, or are immune or not subject to any such legal or
jurisdictional issues, for which it becomes moot.

Similarly, realtime TorDNSEL and the like could be considered
to be censorship enabling tools.

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