[bittorrent] Choice of listener ports

Elliott Mitchell ehem at m5p.com
Sat Mar 26 18:36:41 EST 2005


>From: Kenneth Porter <shiva at sewingwitch.com>
> Traditionally BT peers listen on ports 6881-6889, and trackers on 6969. But 
> those values aren't defined in the protocol; they're just conventions. It 
> occurred to me that one way to deal with blocking is to listen on a port 
> normally used for an "approved" service, such as 25, 80, 110 or 443. (Those 
> using mod_bt to run a tracker inside Apache can run the tracker on the same 
> port as their regular web server. Others could use Apache to proxy port 80 
> requests to their separate tracker program.)
> 
> What problems would you foresee from doing this?

What are you trying to find out? Trackers can be run on whatever port you
wish, clients can be run on whatever port you wish. Just 6969 is the
conventional one for standalone trackers, and 6881-6889 are the
conventional ones for clients. The port choice for the client is helpful
for traffic shaping, but is otherwise arbitrary. There is nothing to
respond to here, yes alternate ports can be used, but they do have
disadvantages.

One big one is low ports are privledged and may be filtered at an ISP
(attempt to stop M$ virii or AUP violations). On clients, you make it
difficult to do traffic shaping. Do either of these cause problems for
implementations? No. The protocol allows for non-conventional setups like
these.


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