Issue about selection of Tor relays when using the default torrc configuration

[Sambuddho Chakravarty]

Hello Scott
 Thanks for you help. However , is there no way that I can cause tor 
client to reload a new set of entry guard nodes  ?  I have tried both 
NEWNYM and HUP signals through *nc* to communicate to tor controller . 
However , in both cases only a small set of (infact 3) entry guards are 
selected.


Thanks
Sambuddho
Scott Bennett wrote:
>      On Fri, 29 May 2009 17:17:33 -0400 Sambuddho Chakravarty
> <sc2516 at columbia.edu> wrote:
>   
>> I am using the default torrc without giving any information on what 
>> relays to select for circuit creation. But apparently tor (from what I 
>> experience) Tor doesn't change the relays selected in a long time. So 
>> each time (over a period of 2 - 3 hours) I start the tor client it seems 
>> to be selecting the same relays  . Is there a way I can ensure different 
>> relay selection over each time I start the tor client.
>>
>>     
>      You may be observing any of several things that lead you to believe
> what you wrote.  For example, The torrc distributed with the package and
> most likely the internal default in the code say that three entry guards
> are to be used.  Entry guard connections can be held open for a very long
> time because all of your client traffic gets funneled through them.  The
> default route length is 3, so each circuit needs at least two more nodes
> beyond the entry guard.  We are fortunate that the tor network includes
> several dozen nodes that handle very large volumes of data at high rates.
> Those nodes, therefore, get chosen frequently during circuit route selection,
> so you may see these popping up over and over again, but regardless of how
> it seems in a Vidalia display, they are being used for new circuits each
> time.  Also, many streams (i.e., TCP connections) may pass simultaneously
> or in succession through the same circuit.  As long as a single stream is
> still present in a circuit, the circuit is considered active and will not
> be torn down, regardless of its age.  The upshot of this is that if you
> have, say, a secure shell login session to your friendly UNIX/LINUX system
> somewhere and you stay logged in, the circuit that connection passes through
> will not normally be closed until you do logout.  (Note that after a circuit
> has aged ten minutes, no *new* streams are to be assigned to it.  New
> streams will be assigned to a new(er) circuit.
>      tor's standard client behavior is to begin aging a circuit the first
> time it is used.  It is important to remember this and to note that the
> first time a circuit is used could conceivably be quite a while after it
> is built because tor builds some circuits in anticipation of needing them.
> Such circuits may end up not being used, but if they aren't, then they will
> hang around anyway for an hour(?) or so before being torn down.
>      If you use a tor controller, such as torctl or Vidalia, you can send
> a NEWNYM command to tor that will cause it to mark all aging circuits (i.e.,
> those that have been or are being used at least once).  Any circuits that
> are aging but have no streams in them (i.e., the circuits are not currently
> active) and get marked as "old" this way will automatically be torn down.
> Any that are currently active will still be marked "old", so that they can
> be torn down when they become inactive.  When tor has no available circuits
> to assign a new stream to, it will begin building some new ones.  I confess
> I don't recall offhand whether a NEWNYM or a SIGHUP will by itself cause
> tor to build circuits preemptively (i.e., in anticipation of need for them).
> The last time I used a version of Vidalia, it had some cute button to click
> on that said, "New Identity" or some such thing.
>
>
>                                   Scott Bennett, Comm. ASMELG, CFIAG
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> * Internet:       bennett at cs.niu.edu                              *
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