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FTP server-server interaction - II (RFC0478)

IP.com Disclosure Number: IPCOM000004928D
Original Publication Date: 1973-Mar-01
Included in the Prior Art Database: 2019-Feb-12
Document File: 2 page(s) / 3K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

R.D. Bressler: AUTHOR [+1]

Related Documents

10.17487/RFC0478: DOI

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 81% of the total text.

Network Working Group B. Bressler Request for Comments: 478 B. Thomas NIC: 14947 BBN 26 March 1973

FTP Server-Server Interaction-II

At the recent FTP meeting at BBN in Cambridge, one of the topics discussed was that of server-server interaction. In a typical situation a user (A) conversing with two servers (B,C) is interested in retrieving a file from one site (B) and sending it to the other (C).

+------+ | USER | | A | /+------+\ control control / \ +------+ +------+ |SERVER| DATA |SERVER| | B |----------->| C | +------+ +------+

The consensus of the meeting was that mechanisms were necessary to make B and C aware of each other and to allow a data connection to be established without forcing each other to queue RFCs for local sockets before they exist.

The proposed solution to this problem was a command called PASSIVE (PASV?). The following is our conclusion as to the meaning of the command and how it would be used.

Third party connections would be established using the SOCK command, which says "Be prepared to use socket S at Host H to establish your data connection", and the PASV command which says "open your data socket for listening, and upon receipt of a transfer command wait for an RFC rather than initiating one."

A positive acknowledgement to the PASV command indicates that the data socket has been opened for listening. When an RFC for its data socket arrives after it has positively acknowledged a PASV command, the server should respond with a matching RFC to open the data connection (assuming, of course, that the incoming RFC is consistent with the previous SOCK commands, if any).

Bressler [Page 1]

RFC 478 FTP Server-Server Interaction-II 26 March 1973

+---------------+ | | +----------| USER PROCESS |----------+ | | A | | telnet +---------------+ telnet | | | | +-----------+ +-------------+ | |--------> --------->| | | SERVER |data sockets data socket| SERVER | | B | Sb Sc | C | | |<-------- <---------| | +-----------+ +-------------+

USER A TO SERVER B USER A TO SERVER C __________________ __________________

A->B SOCK HOST-C SKT- Sc A->C SOCK HOST-B SKT- Sb

B->A ACK C->A ACK

A->B PASV

B->A ACK

A...

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