Path-spec - fast circuits

ilter yüksel ilteryuksel at
Wed Feb 17 10:15:27 UTC 2010

Hello Everyone,

Firstly thank all of you so much for your concern. I really appreciate all
effort which for anonymity by open source.

Mike, I'm reading and trying to understand your changes on path and
dir-spec. Could you say please why there isn't "Wge" integer value on list?
Can't we select a node with exit flag for guard position?

Also could you please explain what is the condition of below statement on
path-spec? ;

"If we're using Guard nodes, the first node must be a Guard (see 5 below )"

It says see 5 below but even i've read 5. section i couldn't get what is the
condition of this statement; "if we're using Guard nodes".

Thanks in advance.

On Mon, Feb 15, 2010 at 4:18 AM, Mike Perry <mikeperry at> wrote:

> Thus spake Nick Mathewson (nickm at
> > 2010/2/12 ilter yüksel <ilteryuksel at>:
> > > "For circuits that do not need to be "fast", when choosing among
> multiple
> > > candidates for a path element, we choose randomly. For "fast" circuits,
> we
> > > pick a given router as an exit with probability proportional to its
> > > bandwidth."
> > >
> > > Could anybody explain why Tor pick exit router with probability
> proportional
> > > to its bandwidth only for fast circuits? As far as i know Tor uses this
> > > technique for load-balance. But why it uses this technique only for
> fast
> > > circuits?
> >
> > First of all, "Fast" circuits are a bit misnamed as used in
> > path-spec.txt.  Basically, "fast" means "bandwidth-sensitive".  The
> > only ones that aren't don't need to be "fast" in this sense are ones
> > that are going to be used only for a tiny amount of traffic.
> >
> > That said, I think the statement in path-spec.txt may be poor.  It
> > probably makes sense to weight all choices by bandwidth, now that
> > bandwidth is measured rather than just being self-advertised.
> >
> > To see what the code is actually doing, the string to search for is
> > need_capacity or NEED_CAPACITY.  The most interesting layer to look
> > for this is at is where it's passed as a flag to
> > circuit_launch_by_router() or circuit_launch_by_extend_info().
> Ok, I've gone ahead and fixed both the spec and the code in
> mikeperry/consensus-bw-weights4 in my git repo.
> --
> Mike Perry
> Mad Computer Scientist
> evil labs
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