
git-svn-id: https://tftpy.svn.sourceforge.net/svnroot/tftpy/trunk@3 63283fd4-ec1e-0410-9879-cb7f675518da
283 lines
9.3 KiB
Text
283 lines
9.3 KiB
Text
|
||
|
||
|
||
|
||
|
||
|
||
Network Working Group G. Malkin
|
||
Request for Commments: 2348 Bay Networks
|
||
Updates: 1350 A. Harkin
|
||
Obsoletes: 1783 Hewlett Packard Co.
|
||
Category: Standards Track May 1998
|
||
|
||
|
||
TFTP Blocksize Option
|
||
|
||
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. One of its primary uses is the booting of diskless
|
||
nodes on a Local Area Network. TFTP is used because it is very
|
||
simple to implement in a small node's limited ROM space. However,
|
||
the choice of a 512-octet blocksize is not the most efficient for use
|
||
on a LAN whose MTU may 1500 octets or greater.
|
||
|
||
This document describes a TFTP option which allows the client and
|
||
server to negotiate a blocksize more applicable to the network
|
||
medium. The TFTP Option Extension mechanism is described in [2].
|
||
|
||
Blocksize Option Specification
|
||
|
||
The TFTP Read Request or Write Request packet is modified to include
|
||
the blocksize option as follows. Note that all fields except "opc"
|
||
are NULL-terminated.
|
||
|
||
+-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+
|
||
| opc |filename| 0 | mode | 0 | blksize| 0 | #octets| 0 |
|
||
+-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+
|
||
|
||
opc
|
||
The opcode field contains either a 1, for Read Requests, or 2,
|
||
for Write Requests, as defined in [1].
|
||
|
||
|
||
|
||
Malkin & Harkin Standards Track [Page 1]
|
||
|
||
RFC 2348 TFTP Blocksize Option May 1998
|
||
|
||
|
||
filename
|
||
The name of the file to be read or written, as defined in [1].
|
||
|
||
mode
|
||
The mode of the file transfer: "netascii", "octet", or "mail",
|
||
as defined in [1].
|
||
|
||
blksize
|
||
The Blocksize option, "blksize" (case in-sensitive).
|
||
|
||
#octets
|
||
The number of octets in a block, specified in ASCII. Valid
|
||
values range between "8" and "65464" octets, inclusive. The
|
||
blocksize refers to the number of data octets; it does not
|
||
include the four octets of TFTP header.
|
||
|
||
For example:
|
||
|
||
+-------+--------+---+--------+---+--------+---+--------+---+
|
||
| 1 | foobar | 0 | octet | 0 | blksize| 0 | 1428 | 0 |
|
||
+-------+--------+---+--------+---+--------+---+--------+---+
|
||
|
||
is a Read Request, for the file named "foobar", in octet (binary)
|
||
transfer mode, with a block size of 1428 octets (Ethernet MTU, less
|
||
the TFTP, UDP and IP header lengths).
|
||
|
||
If the server is willing to accept the blocksize option, it sends an
|
||
Option Acknowledgment (OACK) to the client. The specified value must
|
||
be less than or equal to the value specified by the client. The
|
||
client must then either use the size specified in the OACK, or send
|
||
an ERROR packet, with error code 8, to terminate the transfer.
|
||
|
||
The rules for determining the final packet are unchanged from [1].
|
||
The reception of a data packet with a data length less than the
|
||
negotiated blocksize is the final packet. If the blocksize is
|
||
greater than the amount of data to be transfered, the first packet is
|
||
the final packet. If the amount of data to be transfered is an
|
||
integral multiple of the blocksize, an extra data packet containing
|
||
no data is sent to end the transfer.
|
||
|
||
Proof of Concept
|
||
|
||
Performance tests were run on the prototype implementation using a
|
||
variety of block sizes. The tests were run on a lightly loaded
|
||
Ethernet, between two HP-UX 9000, in "octet" mode, on 2.25MB files.
|
||
The average (5x) transfer times for paths with (g-time) and without
|
||
(n-time) a intermediate gateway are graphed as follows:
|
||
|
||
|
||
|
||
|
||
Malkin & Harkin Standards Track [Page 2]
|
||
|
||
RFC 2348 TFTP Blocksize Option May 1998
|
||
|
||
|
||
|
|
||
37 + g
|
||
|
|
||
35 +
|
||
|
|
||
33 +
|
||
|
|
||
31 +
|
||
|
|
||
29 +
|
||
|
|
||
27 +
|
||
| g blocksize n-time g-time
|
||
25 + --------- ------ ------
|
||
s | n 512 23.85 37.05
|
||
e 23 + g 1024 16.15 25.65
|
||
c | 1428 13.70 23.10
|
||
o 21 + 2048 10.90 16.90
|
||
n | 4096 6.85 9.65
|
||
d 19 + 8192 4.90 6.15
|
||
s |
|
||
17 + g
|
||
| n
|
||
15 +
|
||
| n
|
||
13 +
|
||
|
|
||
11 + n
|
||
| g
|
||
9 +
|
||
|
|
||
7 + n
|
||
| g
|
||
5 + n
|
||
"
|
||
0 +------+------+--+---+------+------+---
|
||
512 1K | 2K 4K 8K
|
||
1428
|
||
blocksize (octets)
|
||
|
||
The comparisons between transfer times (without a gateway) between
|
||
the standard 512-octet blocksize and the negotiated blocksizes are:
|
||
|
||
1024 2x -32%
|
||
1428 2.8x -42%
|
||
2048 4x -54%
|
||
4096 8x -71%
|
||
8192 16x -80%
|
||
|
||
|
||
|
||
Malkin & Harkin Standards Track [Page 3]
|
||
|
||
RFC 2348 TFTP Blocksize Option May 1998
|
||
|
||
|
||
As was anticipated, the transfer time decreases with an increase in
|
||
blocksize. The reason for the reduction in time is the reduction in
|
||
the number of packets sent. For example, by increasing the blocksize
|
||
from 512 octets to 1024 octets, not only are the number of data
|
||
packets halved, but the number of acknowledgement packets is also
|
||
halved (along with the number of times the data transmitter must wait
|
||
for an ACK). A secondary effect is the efficiency gained by reducing
|
||
the per-packet framing and processing overhead.
|
||
|
||
Of course, if the blocksize exceeds the path MTU, IP fragmentation
|
||
and reassembly will begin to add more overhead. This will be more
|
||
noticable the greater the number of gateways in the path.
|
||
|
||
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 Option Extension", RFC 2347,
|
||
May 1998.
|
||
|
||
Authors' Addresses
|
||
|
||
Gary Scott Malkin
|
||
Bay Networks
|
||
8 Federal Street
|
||
Billerica, MA 10821
|
||
|
||
Phone: (978) 916-4237
|
||
EMail: gmalkin@baynetworks.com
|
||
|
||
|
||
Art Harkin
|
||
Networked Computing Division
|
||
Hewlett-Packard Company
|
||
19420 Homestead Road MS 43LN
|
||
Cupertino, CA 95014
|
||
|
||
Phone: (408) 447-3755
|
||
EMail: ash@cup.hp.com
|
||
|
||
|
||
|
||
|
||
Malkin & Harkin Standards Track [Page 4]
|
||
|
||
RFC 2348 TFTP Blocksize Option 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 5]
|
||
|