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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 draft-ietf-tftpexts-tftp-option-ext-01.txt G. Malkin / Xylogics, Inc. 2 TFTP Option Extension A. Harkin / Hewlett-Packard Co. 3 Updates: RFC 1350 (STD 33) October 1994 5 TFTP Option Extension 7 Abstract 9 The Trivial File Transfer Protocol [1] is a simple, lock-step, file 10 transfer protocol which allows a client to get or put a file onto a 11 remote host. This document describes a simple extension to TFTP to 12 allow option negotiation prior to the file transfer. 14 Status of this Memo 16 This document is an Internet-Draft. Internet-Drafts are working 17 documents of the Internet Engineering Task Force (IETF), its areas, 18 and its working groups. Note that other groups may also distribute 19 working documents as Internet-Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six months 22 and may be updated, replaced, or obsoleted by other documents at any 23 time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as "work in progress." 26 To learn the current status of any Internet-Draft, please check the 27 "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow 28 Directories on ds.internic.net (US East Coast), nic.nordu.net 29 (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific 30 Rim). 32 Introduction 34 The option negotiation mechanism proposed in this document is a 35 backward-compatible extension to the TFTP protocol. It allows file 36 transfer options to be negotiated prior to the transfer using a 37 mechanism which is consistent with TFTPs Request Packet format. The 38 mechanism is kept simple by enforcing a request-respond-acknowledge 39 sequence, similar to the lock-step approach taken by TFTP itself. 41 While the option negotiation mechanism is general purpose, in that 42 many types of options may be negotiated (e.g., timeout values), it 43 was created to support the Blocksize option defined in [2]. 45 Packet Formats 47 TFTP options are appended to the Read Request and Write Request 48 packets. A new type of TFTP packet, the Option Acknowledgment 49 (OACK), is used to acknowledge a client's option negotiation request. 50 A new error code, 8, is hereby defined to indicate that a transfer 51 should be terminated due to option negotiation. 53 Options are appended to a TFTP Read Request or Write Request packet 54 as follows: 56 +-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+--> 57 | opc |filename| 0 | mode | 0 | opt1 | 0 | value1 | 0 | < 58 +-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+--> 60 >-------+---+---~~---+---+ 61 < optN | 0 | valueN | 0 | 62 >-------+---+---~~---+---+ 64 opc 65 The opcode field contains either a 1, for Read Requests, or 2, 66 for Write Requests, as defined in [1]. 68 filename 69 The name of the file to be read or written, as defined in [1]. 70 This is a NULL-terminated field. 72 mode 73 The mode of the file transfer: "netascii", "octet", or "mail", 74 as defined in [1]. This is a NULL-terminated field. 76 opt1 77 The first option, in case-insensitive ASCII (e.g., blksize). 78 This is a NULL-terminated field. 80 value1 81 The value associated with the first option, in case-insensitive 82 ASCII. This is a NULL-terminated field. 84 optN, valueN 85 The final option/value pair. Each NULL-terminated field is 86 specified in case-insensitive ASCII. 88 The options and values are all NULL-terminated, in keeping with the 89 original request format. If multiple options are to be negotiated, 90 they are appended to each other. The order in which options are 91 specified is not significant. 93 The OACK packet has the following format: 95 +-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+ 96 | opc | opt1 | 0 | value1 | 0 | optN | 0 | valueN | 0 | 97 +-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+ 99 opc 100 The opcode field contains a 6, for Option Acknowledgment. 102 opt1 103 The first option acknowledgment, copied from the original 104 request. 106 value1 107 The acknowledged value associated with the first option. If 108 and how this value may differ from the original request is 109 detailed in the specification for the option. 111 optN, valueN 112 The final option/value acknowledgment pair. 114 Negotiation Protocol 116 The client appends options at the end of the Read Request or Write 117 request packet, as shown above. Any number of options may be 118 specified; however, an option may only be specified once. The order 119 of the options is not significant. 121 If the server supports option negotiation, and it recognizes one or 122 more of the options specified in the request packet, the server may 123 respond with an Options Acknowledgment (OACK). Each option the 124 server recognizes, and accepts the value for, is included in the 125 OACK. Some options may allow alternate values to be proposed, but 126 this is an option specific feature. The server must not include in 127 the OACK any option which had not been specifically requested by the 128 client; that is, only the client may initiate option negotiation. 129 Options which the server does not support should be omitted from the 130 OACK; they should not cause an ERROR packet to be generated. If the 131 value of a supported option is invalid, the specification for that 132 option will indicate whether the server should simply omit the option 133 from the OACK, respond with an alternate value, or send an ERROR 134 packet, with error code 8, to terminate the transfer. 136 An option not acknowledged by the server must be ignored by the 137 client and server as if it were never requested. If multiple options 138 were requested, the client must use those options which were 139 acknowledged by the server and must not use those options which were 140 not acknowledged by the server. 142 When the client appends options to the end of a Read Request packet, 143 three possible responses may be returned by the server: 145 OACK - acknowledge of Read Request and the options; 147 DATA - acknowledge of Read Request, but not the options; 149 ERROR - the request has been denied. 151 When the client appends options to the end of a Write Request packet, 152 three possible responses may be returned by the server: 154 OACK - acknowledge of Write Request and the options; 156 ACK - acknowledge of Write Request, but not the options; 158 ERROR - the request has been denied. 160 If a server implementation does not support option negotiation, it 161 will likely ignore any options appended to the client's request. In 162 this case, the server will return a DATA packet for a Read Request 163 and an ACK packet for a Write Request establishing normal TFTP data 164 transfer. In the event that a server returns an error for a request 165 which carries an option, the client may attempt to repeat the request 166 without appending any options. This implementation option would 167 handle servers which consider extraneous data in the request packet 168 to be erroneous. 170 Depending on the original transfer request there are two ways for a 171 client to confirm acceptance of a server's OACK. If the transfer was 172 initiated with a Read Request, then an ACK (with the data block 173 number set to 0) is sent by the client to confirm the values in the 174 server's OACK packet. If the transfer was initiated with a Write 175 Request, then the client begins the transfer with the first DATA 176 packet, using the negotiated values. If the client rejects the OACK, 177 then it sends an ERROR packet, with error code 8, to the server and 178 the transfer is terminated. 180 Once a client acknowledges an OACK, with an appropriate non-error 181 response, that client has agreed to use only the options and values 182 returned by the server. Remember that the server cannot request an 183 option; it can only respond to them. If the client receives an OACK 184 containing an unrequested option, it should respond with an ERROR 185 packet, with error code 8, and terminate the transfer. 187 Examples 189 Read Request 191 client server 192 ------------------------------------------------------- 193 |1|foofile|0|octet|0|blksize|0|1432|0| --> RRQ 194 <-- |6|blksize|0|1432|0| OACK 195 |4|0| --> ACK 196 <-- |3|1| 1432 bytes of data | DATA 197 |4|1| --> ACK 198 <-- |3|2| 1432 bytes of data | DATA 199 |4|2| --> ACK 200 <-- |3|3|<1432 bytes of data | DATA 201 |4|3| --> ACK 203 Write Request 205 client server 206 ------------------------------------------------------- 207 |2|barfile|0|octet|0|blksize|0|2048|0| --> RRQ 208 <-- |6|blksize|0|2048|0| OACK 209 |3|1| 2048 bytes of data | --> DATA 210 <-- |4|1| ACK 211 |3|2| 2048 bytes of data | --> DATA 212 <-- |4|2| ACK 213 |3|3|<2048 bytes of data | --> DATA 214 <-- |4|3| ACK 216 Security Considerations 218 Security issues are not discussed in this memo. 220 References 222 [1] Sollins, K., "The TFTP Protocol (Revision 2)", Request for 223 Comments 1350 (STD 33), October 1992. 225 [2] Malkin, G., Harkin, A., "TFTP Blocksize Option", Internet Draft, 226 draft-malkin-tftp-blksize-opt-01.txt, September 1994. 228 Authors' Addresses 230 Gary Scott Malkin 231 Xylogics, Inc. 232 53 Third Avenue 233 Burlington, MA 01803 235 Phone: (617) 272-8140 236 EMail: gmalkin@xylogics.com 238 Art Harkin 239 Internet Services Project 240 Information Networks Division 241 19420 Homestead Road MS 43LN 242 Cupertino, CA 95014 244 Phone: (408) 447-3755 245 EMail: ash@cup.hp.com