Date: Wed, 27 Aug 1997 22:22:49 -0400 From: "Louis A. Mamakos" <louie@TransSys.COM> To: Nate Williams <nate@mt.sri.com> Cc: hackers@FreeBSD.ORG Subject: Re: FTP protocol questions (non-passive mode) Message-ID: <199708280222.WAA07055@whizzo.TransSys.COM> In-Reply-To: Your message of "Wed, 27 Aug 1997 16:34:07 MDT." <199708272234.QAA02520@rocky.mt.sri.com> References: <199708272234.QAA02520@rocky.mt.sri.com>
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Ok, so the client opens a TCP connection to an FTP server: (Client-IP, Client-Port) <-> (Server-IP, 21) in the absense of any other information, the data connection is made (per transfer) as: (Client-IP, Client-Port) <-> (Server-IP, 20) that is, the client reuses the same local port number, but uses the FTP data port on the server. BSD ftp clients use the PORT command to override this default port number selection. This allows successive data transfers to proceed more rapidly since you don't have to wait for the previous connection state to time out (it might be in TIMEWAIT state) before you can re-bind the same port number. louie
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