[tor-relays] Call for discussion: turning funding into more exit relays

Roger Dingledine arma at mit.edu
Mon Jul 23 18:58:54 UTC 2012

For a few years now, funders have been asking if they can pay Tor to
run more relays. I kept telling them their money was better spent on
code and design improvements:
since a) network load would just grow to fill whatever new capacity we
have, especially if we don't deal with the tiny fraction of users who
do bulk downloads, and b) reducing diversity of relay operator control
can harm anonymity.

But lately the Tor network has become noticeably faster, and I think it
has a lot to do with the growing amount of excess relay capacity relative
to network load:

At the same time, much of our performance improvement comes from better
load balancing -- that is, concentrating traffic on the relays that can
handle it better. The result though is a direct tradeoff with relay
diversity: on today's network, clients choose one of the fastest 5 exit
relays around 25-30% of the time, and 80% of their choices come from a
pool of 40-50 relays.

Since extra capacity is clearly good for performance, and since we're
not doing particularly well at diversity with the current approach,
we're going to try an experiment: we'll connect funding to exit relay
operators so they can run bigger and/or better exit relays.

If we do it right (make more faster exit relays that aren't the current
biggest ones, so there are more to choose from), we will improve the
network's diversity as well as being able to handle more users.

We've lined up our first funder (BBG, aka http://www.voanews.com/),
and they're excited to have us start as soon as we can. They want to
sponsor 125+ fast exits.


Open questions we need to decide about:

1) What exactly would we pay for?

I think the right way to do it is to offer to reimburse bandwidth/hosting
costs -- I don't want to get into the business of paying people to
run relays, and I don't want people to be trying to figure out how to
"profit". That leads to all sorts of horrible incentive structures.

More broadly, we should keep in mind that the primary cost of running an
exit relay is effort, not dollars: it takes dedication to find an ISP
who will host it, and to hold that ISP's hand when an abuse complaint
arrives. Or said another way, hosting costs are in many cases not the
biggest barrier to running an exit relay.

I think we should aim to constrain ourselves to talking about >=100mbit
exits, assuming that turns out to give us enough choices. That said,
we don't want to concentrate bandwidth too much in any given relay,
so we should limit the amount we'll reimburse per relay.

2) Should we fund existing relays or new ones?

The worst failure mode here would be that we screw up the current
community of relay operators. That's why it's extra important to keep
them involved at each step of this discussion.

I think the right answer is probably a balance of reimbursing costs from
current exits and encouraging new exits to appear. Before we can get
more precise though, we need to get a handle on how many current fast
exits there are, and what their constraints are (whether their hosting
situation could give them more bandwidth, whether they're paying now or
getting a deal through a friend/employer, etc).

Even then, there are interesting further questions like:

- Should we prefer big collectives like torservers, noisetor, CCC,
dfri.se, and riseup (which can get great bulk rates on bandwidth and are
big enough to have relationships with local lawyers and ISPs), or should
we prefer individuals since they maximize our operator diversity? I think
"explore both approaches" is a fine first plan.

- For existing relays who pay for hosting, should we prefer that our money
go to covering their existing costs (and then we encourage them to save
their money for use, say, after this experiment finishes), or should we
aim to add additional funding so the relay can use more bandwidth? I'd
say it comes down to the preferences of the relay operator. That said, if
we have plenty to choose from, we should pick the relays that will make
the network grow -- but we should take extra care to avoid situations
where operators in the first category say "well, fine" and shut down
their relay.

More generally, we need to consider sustainability. Our current exit
relay funding is for a period of 12 months, and while there's reason to
think we will find continued support, the Tor network must not end up
addicted to external funding. So long as everybody is running an exit
relay because they want to save the world, I think we should be fine.

4) What exactly do we mean by diversity?

There's network diversity (AS / upstream network topology), organization
and operator diversity, jurisdictional (country) diversity, funding
diversity, data-center diversity, and more.

We've started to answer some of these questions at
but this research topic will need ongoing attention. I'd love to get to
the point where our diversity metrics can recommend network locations
that best improve the various diversity scores.

5) How much "should" an exit relay cost?

Since we're aiming for diversity, we can't send all our volunteers to
the same cut-rate German VPS provider. After all, much of the work in
setting up an exit relay is finding a good provider that doesn't already
host a bunch of Tor relays.

But if we declare that we'll reimburse $50/month for 100mbit, we're going
to attract a different set of volunteers -- and a different set of network
locations -- than if we reimburse $100/month for 100mbit. We need to learn
about current bandwidth pricing: I know there are 10 cheap hosting places
that will tolerate exit relays, but are there 200? And do all of those
200 turn out to overlap diversity-wise? Initial guesses appreciated. I'm
inclined toward the $100 number to give our volunteers more flexibility.

If we want to reimburse on a monthly basis, how do we handle situations
where the ISP wants a longer-term contract? I think the answer will come
down to how many choices we have.

6) How exactly should we choose which exit relay operators to reimburse?

It might be premature to speculate until we better understand what choices
are available to us. But I think the answer must include doing it in a way
that encourages continued growth of the relay operator _community_. People
who are active in the Tor community, and well-known to many other people,
should be part of the answer. At the same time, we should be willing to
put some of the money into trying out new places and people, especially
if they're in good locations diversity-wise.

The broader answer is that we as a community need to figure out a good
answer here. I definitely don't want it to be "Roger picks people in
an opaque way". But I also don't want the answer to be "anybody on the
Internet who offers to take our money". Maybe we should put together a
consortium of current Tor activists who run fast exits?

7) How do we audit / track the sponsored relays?

How should we check that your 100mbit relay is really working? What do
we measure to confirm its capacity? To a first approximation I'm fine
assuming that nobody is going to try to cheat (say, by colluding with
an ISP to write legit-looking invoices but then just split the money).

But as the plan scales, we need good ways to track statistics on how
many relays are being sponsored and how much bandwidth they're providing
(so funders can see how effective their money is), and what fraction of
the overall network these sponsored relays are (to keep an eye on the
diversity questions).

8) Legal questions?

Tor exit relays raise plenty of legal questions already, especially when
you consider jurisdiction variety. But reimbursing relays introduces
even more excitement, such as:

- Does such a relay operator end up in a different situation legally?
- Does the overall Tor network change legal categories in some country,
e.g. becoming a telecommunications service when it wasn't before?
- Does The Tor Project Inc incur new liabilities for offering this money?

Tor has a history of creating fascinating new challenges for legal
scholars, and this exit relay funding experiment will be no exception.

I believe if we position it correctly, we won't really change the legal
context. But I encourage people to investigate these questions for
their jurisdiction.


Next steps:

I'm going to do a short blog post pointing to this thread, since many
interested parties aren't on tor-relays yet.

Then I'll send individual emails to exit relay operators pointing them
to it and asking for their feedback (on the list or private, whichever
they prefer). I'll also try to get some sense of how much their hosting
costs, whether they'd want to participate in our experiment, whether
they're in a position to ramp up to a faster connection, etc.

Once we have some concrete facts about how many current exit relays want
to participate, how many new volunteers want to help, and how many ISPs
could handle more exit relays and at what prices, we'll be in a better
position to decide how to proceed.


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