TFTP Option Extension (RFC1782)
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2019-Feb-12
Internet Society Requests For Comment (RFCs)
G. Malkin: AUTHOR [+1]
The Trivial File Transfer Protocol is a simple, lock-step, file transfer protocol which allows a client to get or put a file onto a remote host. This document describes a simple extension to TFTP to allow option negotiation prior to the file transfer.
Network Working Group G. Malkin Request for Comments: 1782 Xylogics, Inc. Updates: 1350 A. Harkin Category: Standards Track Hewlett Packard Co. March 1995
TFTP Option Extension
Status of this Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
The Trivial File Transfer Protocol  is a simple, lock-step, file transfer protocol which allows a client to get or put a file onto a remote host. This document describes a simple extension to TFTP to allow option negotiation prior to the file transfer.
The option negotiation mechanism proposed in this document is a backward-compatible extension to the TFTP protocol. It allows file transfer options to be negotiated prior to the transfer using a mechanism which is consistent with TFTPs Request Packet format. The mechanism is kept simple by enforcing a request-respond-acknowledge sequence, similar to the lock-step approach taken by TFTP itself.
While the option negotiation mechanism is general purpose, in that many types of options may be negotiated, it was created to support the Blocksize option defined in . Additional options are defined in .
This document assumes reader familiarity with the TFTP specification  and its terminology.
TFTP options are appended to the Read Request and Write Request packets. A new type of TFTP packet, the Option Acknowledgment (OACK), is used to acknowledge a client’s option negotiation request. A new error code, 8, is hereby defined to indicate that a transfer should be terminated due to option negotiation.
Malkin & Harkin [Page 1]
RFC 1782 TFTP Option Extension March 1995
Options are appended to a TFTP Read Request or Write Request packet as follows:
+-------+---˜˜---+---+---˜˜---+---+---˜˜---+---+---˜˜---+---+--> | opc |filename| 0 | mode | 0 | opt1 | 0 | value1 | 0 | < +-------+---˜˜---+---+---˜˜---+---+---˜˜---+---+---˜˜---+---+-->
>-------+---+---˜˜---+---+ < optN | 0 | valueN | 0 | >-------+---+---˜˜---+---+
The "0"s shown in these illustrations and the ones below are all all zero octets, i.e., NULL terminators for the preceeding fields.
opc The opcode field contains either a 1, for Read Requests, or 2, for Write Requests, as defined in .
filename The name of the file to be read or written, as defined in . This is a NULL-terminated field.
mode The mode of the file transfer: "netascii", "octet", or "mail", as defined in . This is a NULL-terminated field.
opt1 The first option, in case-insensitive ASCII (e.g., "blksize"). This is a NULL-terminated ASCII field.
value1 The value associated with the first option, in case-insensitive ASCII. This is a NULL-terminated field.
optN, valueN The final option/value pair. Each NULL-terminated...