[tor-relays] A bit more evidence on circuit creation storms

[Gordon Morehouse]

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Roger Dingledine:
> On Thu, Aug 29, 2013 at 11:30:33PM -0400, krishna e bera wrote:
>> On 13-08-29 10:35 PM, Gordon Morehouse wrote:
>>> What on earth is causing so many circuit creation requests in
>>> such a short timespan?

[snip]

> As for the circuit create storm phenomenon... if this is in fact a 
> botnet signing up the million new users, and they're connecting to
> a hidden service C&C site, then I would expect even fiercer create
> storms.
> 
> See also https://trac.torproject.org/projects/tor/ticket/9574


Hi Roger, and thanks for taking the time to respond.  I've definitely
seen an increase in the storms compared to the baseline I established
on my Raspberry Pi after upgrading to 0.2.4.16-rc; but so far only one
crash.  There has been a ripple or two on my bigger VPS relays.

If I could bug you for a sec, I do have some questions about how
circuit creation works in Tor.  I hope you have a moment to answer.

The full message is at:

https://lists.torproject.org/pipermail/tor-relays/2013-August/002589.html

Here is the main set of questions (the "numbers" are in the full message):

> My main question:  How do circuit creation requests on one's Tor
> relay cause load on one's network infrastructure?  Is it DNS
> requests?  Is it TCP connection state entries?  It's not bandwidth,
> we observed that above, and my router can handle far faster pipes
> than the one it's on currently.  The DNS failing is a sign that the
> router is under severe stress.  Back in the 0.2.3.x days, I often
> had to reboot the *router* after one of these storms, not just the
> Tor relay.
> 
> And again - do we really know what is causing this?  Something
> seems seriously wrong with the kind of numbers I'm seeing coming in
> to a node with MaxAdvertisedBandwidth 250KB.

Thanks much,
- -Gordon M.


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