Comments on the File Transfer Protocol (RFC0624)
Original Publication Date: 1974-Feb-28
Included in the Prior Art Database: 2000-Sep-13
Internet Society Requests For Comment (RFCs)
M. Krilanovich: AUTHOR [+4]
There are several aspects of the File Transfer Protocol of RFC 542 that constitute serious drawbacks. Some of these are quite basic in nature, and imply substantial design changes; these will be discussed in a later RFC. Others could be remedied with very little effort, and this should be done as soon as possible.
Network Working Group Mark Krilanovich (UCSB)
Request for Comments: 624 George Gregg (UCSB)
NIC #22054 Wayne Hathaway (AMES-67)
references: RFC 542 Jim White (SRI-ARC)
obsoletes: RFC 607 Feb 1974
Comments on the File Transfer Protocol
This document replaces RFC 607, which was inadvertently released
while still in rough draft form. It would be appreciated if RFC 607
were disregarded, and this document considered the accurate statement
of the authors' opinions.
There are several aspects of the File Transfer Protocol of RFC
542 that constitute serious drawbacks. Some of these are quite basic
in nature, and imply substantial design changes; these will be
discussed in a later RFC. Others could be remedied with very little
effort, and this should be done as soon as possible.
Following is a list of those problems that can be easily solved,
together with their proposed solutions:
1. Once a server has been set to the state where he is "passive"
with regard to establishment of data connections, there is no
convenient way for the user to make him "active" again. The
"REIN" command accomplishes this, but affects more than just the
desired active/passive state. SOLUTION: define a new command,
with a command verb of "ACTV", to mean that the server is to issue
a CONNECT rather than a LISTEN on the data socket. If the server
is already "active", the command is a no op. "ACTV" is to have
the same reply codes as "PASV".
2. Design of an FTP server or user would be simpler if all
command verbs were the same length. While it is certainly
possible to handle varying length verbs, fixed length string
manipulation is in general easier to write and faster to run than
varying length string manipulation, and it would seem that nothing
is to be gained in this application by allowing varying length
strings. SOLUTION: replace the only three-letter verb, "BYE",
with a four-letter one, such as "QUIT", and constrain future
command verbs to be four letters long.
3. The order of the handshaking elements following a file transfer
command is left unspecified. After sending a STOR command, for
example, a user process has no way of knowing which to wait for
first, the "250 FILE TRANSFER STARTED" reply, or establishment of
the data connection. SOLUTION: specify that the server is to
send a "250" reply before attempting to establish the data
connection. If it is desired to check if the user is logged in,
if the file exists, or if the user is to be allowed access to the
file, these checks must be made before any reply is sent. The
text of the "250" reply would perhaps be more appropriate as "250
OPENING DATA CONNECTION", since it comes before actual data
transfer begins. If the server wishes to send an error reply in
the event that the data connection cannot be opened, it is to be
sent in lieu of the "252 TRANSFER COMPLETE" re...