[bittorrent] Tracker is forgetting/currupting my port number

Thad Ward coderjoe at grnet.com
Thu May 25 09:23:01 EDT 2006


An idea as to what might be happening has come to me recently. I think
that these random ports you're seeing are from peers attempting to send
data to your old outgoing port number. When your client needs to connect
out, it uses some port number that is not currently in use (usually) between
1025 and 65535. Apparently, clients send DHT communication via UDP to the
port they were talking to you on for the TCP peer connection. I think
that the DHT-capable clients should only be sending the UDP packets if
they know that you're listening on that port (ie, they connected to you,
rather than the other way around) from their DHT port. This way,
everyone can be sure the DHT packets are going where they should, and
people without ports forwarded will still get their DHT packets, as most
consumer routers will auto-forward UDP packets from a IP/port that it
saw an outbound packet to. (Although it is likely to mangle the source
port of the packet when it does NAT, anyway. hmm..)

Anyway, that's what I think might be going on with these packets you're
seeing.

On Wed, Apr 26, 2006 at 12:17:19PM +1200, Mark Curly wrote:
> Since these are UDP packets, I now believe this is a problem with DHT.
> 
> ----- Original Message ----- 
> From: "Mark Curly" <markcurly at hotmail.com>
> To: <bittorrent at lists.ibiblio.org>
> Sent: Saturday, April 15, 2006 5:24 PM
> Subject: Tracker is forgetting/currupting my port number
> 
> 
> > I think I've found a bug in a tracker.
> >
> > I setup my client and configure my port number.
> > I connect to a few trackers and download a few files.
> > I exit my client.
> >
> > Then my firewall shows incoming refused UDP packets to the target torrent
> > port, from many source IPs.
> > All very good and expected: "Afterglow".
> >
> > Then several hours later it starts showing incoming refused packets to a
> > different port, from many source IPs.
> > What?
> > Then again several hours later, same again with a different target port.
> >
> > It looks like the tracker has forgotten/mangled my bittorrent port number,
> > and is telling clients the wrong port.
> > Those clients then 'ping' (a bencoded ping) me, but with the wrong target
> > port number.
> > (I have a static IP BTW.)
> >
> > I can't easily tell which torrent or tracker has the problem, but maybe
> > someone smarter than me could help me identify the tracker, or put me
> right
> > on what is happening?
> >
> > To be clear, my concern is just the (apparent) bug in the software used by
> > that tracker, and other trackers.
> > I could care less that I'm getting pinged for that particular torrent: my
> > firewall just throws that stuff away.
> >
> > If it is too difficult to track down the tracker and what software it
> might
> > be using, then just ignore me :-)
> >
> > Thanks,
> > Curly
> >
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