Port forwarding not needed...

Hello,

I am confused about the theory or inner workings of port forwarding.
If I have a network with 2 computers running behind a router which
effectively shares 1 IP between the 2 computers... and they both
listen on port 8000... the calls to listen and bind should return
successfully right? What happens (without port forwarding) when
someone trys to connect to this network on port 8000?

I find this weird, because when I run Bit Torrent, it seems to work OK
even without port forwarding... how is this possible?

Thanks!
julia

On 6 May 2004 07:50:56 -0700, Julia Goolia <(E-Mail Removed)> wrote:
> Hello,
>
> I am confused about the theory or inner workings of port forwarding.
> If I have a network with 2 computers running behind a router which
> effectively shares 1 IP between the 2 computers... and they both
> listen on port 8000... the calls to listen and bind should return
> successfully right? What happens (without port forwarding) when
> someone trys to connect to this network on port 8000?
>
> I find this weird, because when I run Bit Torrent, it seems to work OK
> even without port forwarding... how is this possible?

When 2 computers are behind NAT or masquerade, if they make an outgoing
connection, the NAT/masq actually uses a different source port and/or
id in the packet out the public IP, so it knows where to forward a
related reply (or in some cases even if the reply comes to a different
related port).

However, if you had 2 PC's behind NAT/masq both listening on port 8000,
and a connection from outside was initiated to port 8000 on your public
IP, the NAT/masq box would not know what to do with that, unless the
NAT/masq box either had something listening on that port that knew what to
do with it, or was set to forward that public iport to a single internal
iport.

I am not familiar with Bit Torrent, but if it broadcasts like other file
sharing programs, the other end would know what public port or packet id
to use to reach a particular internal IP, based on your outgoing packets.

--
David Efflandt - All spam ignored http://www.de-srv.com/