[tor-dev] Tor path selection upon failure

Liu, Zhuotao zliu48 at illinois.edu
Wed Sep 14 01:37:29 UTC 2016

Thanks for your notes. Tim. :) 

From: tor-dev [tor-dev-bounces at lists.torproject.org] on behalf of teor [teor2345 at gmail.com]
Sent: Tuesday, September 13, 2016 19:42
To: tor-dev at lists.torproject.org
Subject: Re: [tor-dev] Tor path selection upon failure

> On 14 Sep 2016, at 07:28, Liu, Zhuotao <zliu48 at illinois.edu> wrote:
> Hi Folks,
> There have been some technical reports about how to deal with the problem when a botnet uses Tor as its primary C&C channel. In this case, the CPU of some relays is exhausted, causing circuit creation failure.
> I am wondering currently how a client reacts when its circuit creation fails? Does the client simply resends create cells to the relays on the original path or it will re-select a new path instead?

I think the Tor client selects a new path, with a new Exit, HSDir, Intro Point, or Rendezvous Point (within various constraints).
In the Exit case, it will try 3 different paths to 3 Exit relays that claim to allow exiting to the port it wants, then return a failure to the application that made the request.


Tim Wilson-Brown (teor)

teor2345 at gmail dot com
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