mirror of
https://gitlab.torproject.org/tpo/core/tor.git
synced 2024-11-24 20:33:31 +01:00
98 lines
4.2 KiB
Plaintext
98 lines
4.2 KiB
Plaintext
|
|
Right now as I understand it, there are n big scaling problems heading
|
|
our way:
|
|
|
|
1) Clients need to learn all the relay descriptors they could use. That's
|
|
a lot of bytes through a potentially small pipe.
|
|
2) Relays need to hold open TCP connections to most other relays.
|
|
3) Clients need to learn the whole networkstatus. Even using v3, as
|
|
the network grows that will become unwieldy.
|
|
4) Dir mirrors need to mirror all the relay descriptors; eventually this
|
|
will get big too.
|
|
|
|
Here's my plan.
|
|
|
|
--------------------------------------------------------------------
|
|
|
|
Piece one: download O(1) descriptors rather than O(n) descriptors.
|
|
|
|
We need to change our circuit extend protocol so it fetches a relay
|
|
descriptor at every 'extend' operation:
|
|
- Client fetches networkstatus, picks guards, connects to one.
|
|
- Client picks middle hop out of networkstatus, asks guard for
|
|
its descriptor, then extends to it.
|
|
- Clients picks exit hop out of networkstatus, asks middle hop
|
|
for its descriptor, then extends to it. Done.
|
|
|
|
The client needs to ask for the descriptor even if it already has a
|
|
copy, because otherwise we leak too much. Also, the descriptor needs to
|
|
be padded to some large (but not too large) size to prevent the middle
|
|
hops from guessing about it.
|
|
|
|
The first step towards this is to instrument the current code to see
|
|
how much of a win this would actually be -- I am guessing it is already
|
|
a win even with the current number of descriptors.
|
|
|
|
We also would need to assign the 'Exit' flag more usefully, and make
|
|
clients pay attention to it when picking their last hop, since they
|
|
don't actually know the exit policies of the relays they're choosing from.
|
|
|
|
We also need to think harder about other implications -- for example,
|
|
a relay with a tiny exit policy won't get the Exit flag, and thus won't
|
|
ever get picked as an exit relay. Plus, our "enclave exit" model is out
|
|
the window unless we figure out a cool trick.
|
|
|
|
More generally, we'll probably want to compress the descriptors that we
|
|
send back; maybe 8k is a good upper bound? I wonder if we could ask for
|
|
several descriptors, and bundle back all of the ones that fit in the 8k?
|
|
|
|
We'd also want to put the load balancing weights into the networkstatus,
|
|
so clients can choose fast nodes more often without needing to see the
|
|
descriptors. This is a good opportunity for the authorities to be able
|
|
to put "more accurate" weights in if they learn to detect attacks. It
|
|
also means we should consider running automated audits to make sure the
|
|
authorities aren't trying to snooker everybody.
|
|
|
|
I'm aiming to get Peter Palfrader to tackle this problem in mid 2008,
|
|
but I bet he could use some help.
|
|
|
|
--------------------------------------------------------------------
|
|
|
|
Piece two: inter-relay communication uses UDP
|
|
|
|
If relays send packets to/from other relays via UDP, they don't need a
|
|
new descriptor for each such link. Thus we'll still need to keep state
|
|
for each link, but we won't max out on sockets.
|
|
|
|
Clearly a lot more work needs to be done here. Ian Goldberg has a student
|
|
who has been working on it, and if all goes well we'll be chipping in
|
|
some funding to continue that. Also, Camilo Viecco has been doing his
|
|
PhD thesis on it.
|
|
|
|
--------------------------------------------------------------------
|
|
|
|
Piece three: networkstatus documents get partitioned
|
|
|
|
While the authorities should be expected to be able to handle learning
|
|
about all the relays, there's no reason the clients or the mirrors need
|
|
to. Authorities should put a cap on the number of relays listed in a
|
|
single networkstatus, and split them when they get too big.
|
|
|
|
We'd need a good way to have each authority come to the same conclusion
|
|
about which partition a given relay goes into.
|
|
|
|
Directory mirrors would then mirror all the relay descriptors in their
|
|
partition. This is compatible with 'piece one' above, since clients in
|
|
a given partition will only ask about descriptors in that partition.
|
|
|
|
More complex versions of this design would involve overlapping partitions,
|
|
but that would seem to start contradicting other parts of this proposal
|
|
right quick.
|
|
|
|
Nobody is working on this piece yet. It's hard to say when we'll need
|
|
it, but it would be nice to have some more thought on it before the week
|
|
that we need it.
|
|
|
|
--------------------------------------------------------------------
|
|
|