draft proposal: download server descriptors on demand [141]

[Roger Dingledine]

On Mon, Jun 16, 2008 at 12:06:44AM +0200, Peter Palfrader wrote:
> 3.3 Protocol versions
> 
>   [XXX: find out where we need "opt protocols Link 1 2 Circuit 1"
>   information described in 2.3 above.  If we need it, it might have
>   to go into the consensus document.]

Currently, we don't even parse the "opt protocols" line out of the
descriptor, nor do we put it in the consensus. But the plan eventually
is to put it in the consensus, appended to the "v Tor 0.2.0.30" line.
Once we bump the Circuit protocol number, clients will need to be able
to predict what circuit protocol the relays in their path can handle,
and they'll use the consensus to learn that.

Check out e.g. http://archives.seul.org/or/dev/Mar-2007/msg00041.html
for all the gory details.

>   In order to answer that request B obviously needs a copy of C's server
>   descriptor.  In the future we might amend RELAY_REQUEST_SD cells to
>   contain also the expected IP address and OR-port of the server C (the
>   client learns them from the network status document), so that B no
>   longer needs to know all the descriptors of the entire network but
>   instead can simply go and ask C for its descriptor before passing it
>   back to the client.

This seems like a great move -- it means that we can still be compatible
with having a larger network, though if we don't have the descriptor
cached yet it'll slow down those connections.

--Roger