an up2date idea

Don dnrlinux at san.rr.com
Tue Jan 13 22:40:41 UTC 2004


>> It's doable, but I don't think BT does that now... it just assumes
certain
>> ports are open...
>
>I don't remember how it works, but I've seen some machines running it
>(and sharing) from behind a NAT.
>
>If it sends a "here I am", the connection could be done from this point
>- once it begun inside. I don't know if bt is smart enough though.

Yes, exactly. The "here I am" is not required to do the download part. It is
needed to keep a NAT path, and access list open so an incoming request to my
machine will be received.

The "here I am" message basically says "I'm listening on port xxxx at
address 1.2.3.4". Then, when somebody else wants to down load a file and
they go to a BT aware server, that server might tell them... "Yes, go get it
from TCP 1.2.3.4:xxxx".

As long as my NAT translation AND access list still permit that specific
traffic, all should be OK.

Keep in mind the "Here I am" message should not actually embed the port
number nor IP address. Each of those may be changed by NAT along the way.
Instead the BT server will see the incoming address from my machine, and the
port.

As I say, it's doable, I just don't know enough of the internals of BT to
say for certain. Since my firewall access lists are dynamic, in my case,
regardless of NAT

Don





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