Subject: Re: IP-NAT and DCC
To: Guido Falsi +-|- <>
From: Andrew Brown <>
List: netbsd-users
Date: 05/06/1999 16:22:29
>> FTP is a nailed down port, is it not? I think you can probably do outbound
>> DCC connections fine, but I'm not sure how you can manage doing inbound
>> connections. (I don't actually know enough about DCC to know how it works
>no, dcc is a very strange protocol I don't know much about it either,
>but I can accept inbound offers, but others cannot accept my offers
>This appens becouse when I want to send a file I send an offer
>throught the irc server, then the person to which I want to send the
>file accepts the offer and his client connects to mine to start the
>transfer, I think the port to which the person must connect is
>specified in the dcc offer, so I don't think nat can guess it in any
>easy way :-(

the request itself travels over the irc connection between the irc
client and the irc server.  so the endpoint of the server connection
is "well known" (like ftp's command connection is well known), but not
as well known as you might like it to be.  irc servers commonly run on
ports 6665-6669, but there's absolutely nothing stopping anyone from
running one on a completely different port.  the messages sent to the
server from your client are:

  NOTICE otherguy :DCC Send filename.txt (
  PRIVMSG otherguy :^ADCC SEND filename.txt 3232239231 1054 477^A

where the "privmsg" command is the important one.  that's the one that
tells the remote client (the other guy) where to connect back to by
specifying your address as a single, unsigned integer, then the port,
and then some other number.  needless to say, dcc isn't covered in the
irc rfc.  :)

>> on the port level, so I'm pretty much just guessing. I *think* not having
>> a nailed-down port will be an issue, though.)
>The problem is that dcc doesn't have any nailed down ports..., it doesn't.  and less so that ftp.  :)

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