draft-masotta-tftpexts-windowsize-opt-05.txt Patrick Masotta/Vercot Intended status: Informational INTERNET-DRAFT Nov 2012 Expires: Apr 09, 2013 TFTP Windowsize Option 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 early stages of nodes booting from a Local Area Network. TFTP has been always used because it is very simple to implement. However, the choice of a lock-step schema is not the most efficient for use on a LAN. This document describes a TFTP option which allows the client and server to negotiate a windowsize of consecutive blocks to send as an alternative for replacing the single block lock-step schema. The TFTP Option Extension mechanism is described in [2]. Legal This documents and the information contained therein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION THEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Distribution of this draft is unlimited. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Patrick Masotta Expires Apr 09, 2013 [Page 1] Internet Draft TFTP Windowsize Option Nov 2012 Introduction While virtually unused for internet transfers today, TFTP is still massively used in network boot and network installation scenarios. The protocol inherently low transfer rate has been so far partially mitigated by the use of the blocksize negotiated extension [3]. This way the original 512 byte blocks are in practice replaced on Ethernet environments by blocks no larger than 1468 Bytes to avoid IP block fragmentation. The former strategy results insufficient when it comes to transfer big files i.e. the initial ram-disk of live distributions of Linux or the PE images of Microsoft WDS net install scenarios. Considering TFTP looks today far from extinction this draft formally presents a natural extension, already implemented by some companies, that produces TFTP transfer rates comparable to the ones achieved by modern file transfer protocols. Windowsize Option Specification The TFTP Read Request or Write Request packet is modified to include the windowsize option as follows. Note that all fields except "opc" are NULL-terminated. +-------+---~~---+---+---~~---+---+-----~~-----+---+---~~---+---+ | opc |filename| 0 | mode | 0 | windowsize | 0 | #blocks| 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]. mode The mode of the file transfer: "netascii", "octet", or "mail", as defined in [1]. windowsize The Windowsize option, "windowsize" (case in-sensitive). #blocks The number of blocks in a window, specified in ASCII. Valid values range between "1" and "65535" blocks, inclusive. The windowsize refers to the number of consecutives blocks transmited before stop and wait for the reception of the acknowledgment of the last block transmited. For example: +-------+--------+---+-------+---+------------+---+------+---+ | 1 | foobar | 0 | octet | 0 | windowsize | 0 | 16 | 0 | +-------+--------+---+-------+---+------------+---+------+---+ Patrick Masotta Expires Apr 09, 2013 [Page 2] Internet Draft TFTP Windowsize Option Nov 2012 is a Read Request, for the file named "foobar", in octet transfer mode, with a window-size of 16 blocks (as option blocksize is not negotiated in this case, the 512 Bytes per block default applies). If the server is willing to accept the windowsize 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] and [3]. The reception of a data window with a number of blocks less than the negotiated windowsize is the final window. If the windowsize is greater than the amount of data to be transferred, the first window is the final window. Proof of Concept Performance tests were run on the prototype implementation using a variety of windowsizes and a fixed blocksize of 1456 bytes. The tests were run on a lightly loaded Gigabit Ethernet, between two Toshiba Tecra Core 2 Duo 2.2 Ghz, in "octet" mode, transfering a 180 MByte file. ^ 300 + Seconds | windowsize | time(s) | --------- ------ | x 1 257 250 + 2 131 | 4 76 | 8 54 | 16 42 200 + 32 38 | 64 35 | | 150 + | | x | 100 + | | x | 50 + x | x | x x | 0 +-//--+-----+-----+-----+-----+-----+-----+--> 1 2 4 8 16 32 64 windowsize (in blocks of 1456 bytes) Patrick Masotta Expires Apr 09, 2013 [Page 3] Internet Draft TFTP Windowsize Option Nov 2012 The comparison of transfer times (without a gateway) between the standard lock-step schema and the negotiated windowsizes are: 1 -0% 2 -49% 4 -70% 8 -79% 16 -84% 32 -85% 64 -86% As it was expected, the transfer time decreases with the use of a windowed schema. The reason for the reduction in time is the reduction in the number of the required synchronous acknowledgements exchanged. Comparatively the same 180 MB transfer performed over an SMB/CIFS mapped drive took 23 seconds. Error Handling In case of an error detection the whole windowsize window is retransmited. [Requester]<---------------->[Provider] <-traffic-> file block# window block# ... (windowsize=3) <- | n+1 | 1 <- | n+2 | 2 <- | n+3 | 3 |ACK n+3| -> <- | n+4 | 1 Error | n+5 | 2 <- | n+6 | 3 <- | n+4 | 1 <- | n+5 | 2 <- | n+6 | 3 |ACK n+6| -> ... Section of a transfer including error and error recovery Security Considerations The basic TFTP protocol does not have an explicit security mechanism. However it also does not have list, rename, delete, nor overwrite capabilities either. This document does not add any security to TFTP nor the specified extension adds any additional security risk either. IANA Considerations This document has no actions for IANA. Patrick Masotta Expires Apr 09, 2013 [Page 4] Internet Draft TFTP Windowsize Option Nov 2012 Normative References [1] Sollins, K., "The TFTP Protocol (Revision 2)", RFC 1350 (STD 33), October 1992. [2] Malkin, G., Harkin, A., "TFTP Option Extension", RFC 2347 May 1998. [3] Malkin, G., Harkin, A., "TFTP Blocksize option", RFC 2348 May 1998. Authors' Addresses Patrick Masotta 300 W 11th Avenue, #9A Denver, CO 80204 EMail: masotta[-at-]vercot[-dot-]com Copyright and IPR Provisions Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. 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No language to the contrary, or terms, conditions or rights that differ from or are inconsistent with the rights and licenses granted under RFC 5378, shall have any effect and shall be null and void, whether published or posted by such Contributor, or included with or in such Contribution. Patrick Masotta Expires Apr 09, 2013 [Page 5]