[tor-dev] Tor and BGP integration

Jacob Appelbaum jacob at appelbaum.net
Thu Jun 9 14:59:55 UTC 2011

Hello from Iceland,

Linus invited me to Reykjavik to talk about Tor at the NORDUnet conference
and this idea is the result of a bit of feedback from some network operators

Tor needs a way to be friendly to large network operators who wish to enable
exiting to anonymous communication for their networks. These network
operators are happy to allow anyone to pass traffic to their relays as entry
nodes, middle nodes and even limited exit nodes.

Linus and I have been discussing methods of automating this process and of
course BGP integration makes a lot of sense. Generally, a network operator
has a set of AS numbers for their network blocks and as they want people to
connect to many of their services, it helps quite a bit to allow exiting to
those services from their own Tor relays.

We came up with two main ideas for making this happen.

One method would be to write a program where given an AS number and a BGP
feed, we parse all of the advertised network blocks and emit exit policy
lines that accepts all traffic for the AS. This would allow for a web
service similar to BulkExitList.py for network aware exit policy generation
and relay operators would simply need to add this to their Tor configs
manually. For mostly static networks, a cronjob would be fine and Tor
doesn't need to know about AS numbers internally.

Another method would be to write a controller that watches for BGP network
updates and Tor would add relevant exit policy lines for any configured AS.
This would allow any Tor relay to dynamically learn about network changes if
it has access to a BGP feed patched into a controller. This could be
implemented by adding some configuration options to Tor that let Tor know
which AS numbers matter to which router. It may also allow for the router to
auto learn it's own likely family network but it lacks any kind of
bi-directional confirmation, still it seems useful information to have...

It would be fantastic if someone offered a hidden service NORDUNet BGPMon
feed. This would help enable the first method of generating network aware
exit policies; this would also help with the development of AS awareness in
Tor itself. In the future, I imagine that it makes a lot of sense for
circuit building to be BGP aware as mere netblocks will not be very useful
in an ipv6 world, they're already mostly irrelevant.

Anyway, food for thought. Linus and I will probably hack on some of these
ideas in the near future.

All the best,
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