[tor-talk] Double-checking a couple questions about node churn rate

[Karsten Loesing]

Hello Jeremy,

On 08/10/14 00:57, Jeremy Gillula wrote:
> I have a couple questions which I could probably find the answer to on
> my own by writing up some scripts and doing a little research, but I
> figured I'd ask here first in case anyone already knows the answer and
> can take 30 seconds to reply:
> 
> 1. Does anyone have an idea of what the usual churn rate is for Tor
> nodes? (I'm guessing fairly low for most nodes, but if anyone has even
> rough numbers, that would help...)

As one random starting point for your research, take a look at Figure
4.5 on page 83 (page 106 in the PDF, 2.9M):

http://freehaven.net/anonbib/cache/loesing2009thesis.pdf

> 2. How common is it for a node to change its exit policy and go from
> being a relay-only node to an exit node (and vice versa)? If a node did
> change, how quickly would that be reflected in Onionoo? (I'm guessing
> the answers are rare and at most an hour after the change, respectively.)

My *guess* is that this doesn't happen very often, but I don't have any
numbers.  And yes, Onionoo should know it after at most two hours.

> I realize these are vague questions, so even
> order-of-magnitude-rough-guess answers would be appreciated!

If you want to do some more analysis, fetch the latest consensus
tarball(s) and write a script that compares contained fingerprints ("r"
lines) for the churn question and exit policy summaries ("p" lines) for
the exit-policy-change question:

https://collector.torproject.org/archive/relay-descriptors/consensuses/

Example:

[...]
valid-after 2014-10-08 01:00:00
[...]
r gabelmoo 8gREE9rC4C49a89HNaGbyh3pcoE VFtJRYsyCcBUlLVV6wow2hh/Y5g
2014-10-07 10:01:26 131.188.40.189 443 80
s Authority HSDir Running Stable V2Dir Valid
v Tor 0.2.5.8-rc
w Bandwidth=20 Unmeasured=1
p reject 1-65535
[...]

Parsing libraries are available here:

https://collector.torproject.org/#libraries

If you have some interesting results, please feel free to share them here!

All the best,
Karsten