1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395
|
Network Working Group G. Malkin
Request for Commments: 2347 Bay Networks
Updates: 1350 A. Harkin
Obsoletes: 1782 Hewlett Packard Co.
Category: Standards Track May 1998
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.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
Abstract
The Trivial File Transfer Protocol [1] 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.
Introduction
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 TFTP's 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 [2]. Additional options are defined
in [3].
Packet Formats
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
Malkin & Harkin Standards Track [Page 1]
RFC 2347 TFTP Option Extension May 1998
should be terminated due to option negotiation.
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 |
>-------+---+---~~---+---+
opc
The opcode field contains either a 1, for Read Requests, or 2,
for Write Requests, as defined in [1].
filename
The name of the file to be read or written, as defined in [1].
This is a NULL-terminated field.
mode
The mode of the file transfer: "netascii", "octet", or "mail",
as defined in [1]. This is a NULL-terminated field.
opt1
The first option, in case-insensitive ASCII (e.g., blksize).
This is a NULL-terminated 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 field is
specified in case-insensitive ASCII.
The options and values are all NULL-terminated, in keeping with the
original request format. If multiple options are to be negotiated,
they are appended to each other. The order in which options are
specified is not significant. The maximum size of a request packet
is 512 octets.
The OACK packet has the following format:
Malkin & Harkin Standards Track [Page 2]
RFC 2347 TFTP Option Extension May 1998
+-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+
| opc | opt1 | 0 | value1 | 0 | optN | 0 | valueN | 0 |
+-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+
opc
The opcode field contains a 6, for Option Acknowledgment.
opt1
The first option acknowledgment, copied from the original
request.
value1
The acknowledged value associated with the first option. If
and how this value may differ from the original request is
detailed in the specification for the option.
optN, valueN
The final option/value acknowledgment pair.
Negotiation Protocol
The client appends options at the end of the Read Request or Write
request packet, as shown above. Any number of options may be
specified; however, an option may only be specified once. The order
of the options is not significant.
If the server supports option negotiation, and it recognizes one or
more of the options specified in the request packet, the server may
respond with an Options Acknowledgment (OACK). Each option the
server recognizes, and accepts the value for, is included in the
OACK. Some options may allow alternate values to be proposed, but
this is an option specific feature. The server must not include in
the OACK any option which had not been specifically requested by the
client; that is, only the client may initiate option negotiation.
Options which the server does not support should be omitted from the
OACK; they should not cause an ERROR packet to be generated. If the
value of a supported option is invalid, the specification for that
option will indicate whether the server should simply omit the option
from the OACK, respond with an alternate value, or send an ERROR
packet, with error code 8, to terminate the transfer.
An option not acknowledged by the server must be ignored by the
client and server as if it were never requested. If multiple options
were requested, the client must use those options which were
acknowledged by the server and must not use those options which were
not acknowledged by the server.
Malkin & Harkin Standards Track [Page 3]
RFC 2347 TFTP Option Extension May 1998
When the client appends options to the end of a Read Request packet,
three possible responses may be returned by the server:
OACK - acknowledge of Read Request and the options;
DATA - acknowledge of Read Request, but not the options;
ERROR - the request has been denied.
When the client appends options to the end of a Write Request packet,
three possible responses may be returned by the server:
OACK - acknowledge of Write Request and the options;
ACK - acknowledge of Write Request, but not the options;
ERROR - the request has been denied.
If a server implementation does not support option negotiation, it
will likely ignore any options appended to the client's request. In
this case, the server will return a DATA packet for a Read Request
and an ACK packet for a Write Request establishing normal TFTP data
transfer. In the event that a server returns an error for a request
which carries an option, the client may attempt to repeat the request
without appending any options. This implementation option would
handle servers which consider extraneous data in the request packet
to be erroneous.
Depending on the original transfer request there are two ways for a
client to confirm acceptance of a server's OACK. If the transfer was
initiated with a Read Request, then an ACK (with the data block
number set to 0) is sent by the client to confirm the values in the
server's OACK packet. If the transfer was initiated with a Write
Request, then the client begins the transfer with the first DATA
packet, using the negotiated values. If the client rejects the OACK,
then it sends an ERROR packet, with error code 8, to the server and
the transfer is terminated.
Once a client acknowledges an OACK, with an appropriate non-error
response, that client has agreed to use only the options and values
returned by the server. Remember that the server cannot request an
option; it can only respond to them. If the client receives an OACK
containing an unrequested option, it should respond with an ERROR
packet, with error code 8, and terminate the transfer.
Malkin & Harkin Standards Track [Page 4]
RFC 2347 TFTP Option Extension May 1998
Examples
Read Request
client server
-------------------------------------------------------
|1|foofile|0|octet|0|blksize|0|1432|0| --> RRQ
<-- |6|blksize|0|1432|0| OACK
|4|0| --> ACK
<-- |3|1| 1432 octets of data | DATA
|4|1| --> ACK
<-- |3|2| 1432 octets of data | DATA
|4|2| --> ACK
<-- |3|3|<1432 octets of data | DATA
|4|3| --> ACK
Write Request
client server
-------------------------------------------------------
|2|barfile|0|octet|0|blksize|0|2048|0| --> RRQ
<-- |6|blksize|0|2048|0| OACK
|3|1| 2048 octets of data | --> DATA
<-- |4|1| ACK
|3|2| 2048 octets of data | --> DATA
<-- |4|2| ACK
|3|3|<2048 octets of data | --> DATA
<-- |4|3| ACK
Security Considerations
The basic TFTP protocol has no security mechanism. This is why it
has no rename, delete, or file overwrite capabilities. This document
does not add any security to TFTP; however, the specified extensions
do not add any additional security risks.
References
[1] Sollins, K., "The TFTP Protocol (Revision 2)", STD 33, RFC 1350,
October 1992.
[2] Malkin, G., and A. Harkin, "TFTP Blocksize Option", RFC 2348,
May 1998.
[3] Malkin, G., and A. Harkin, "TFTP Timeout Interval and Transfer
Size Options", RFC 2349, May 1998.
Malkin & Harkin Standards Track [Page 5]
RFC 2347 TFTP Option Extension May 1998
Authors' Addresses
Gary Scott Malkin
Bay Networks
8 Federal Street
Billerica, MA 01821
Phone: (978) 916-4237
EMail: gmalkin@baynetworks.com
Art Harkin
Internet Services Project
Information Networks Division
19420 Homestead Road MS 43LN
Cupertino, CA 95014
Phone: (408) 447-3755
EMail: ash@cup.hp.com
Malkin & Harkin Standards Track [Page 6]
RFC 2347 TFTP Option Extension May 1998
Full Copyright Statement
Copyright (C) The Internet Society (1998). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Malkin & Harkin Standards Track [Page 7]
|