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Ciavattone 4 Updates: 5357 (if approved) AT&T Labs 5 Intended status: Standards Track May 30, 2010 6 Expires: December 1, 2010 8 TWAMP Reflect Octets and Symmetrical Size Features 9 draft-ietf-ippm-twamp-reflect-octets-06 11 Abstract 13 The IETF has completed its work on the core specification of TWAMP - 14 the Two-Way Active Measurement Protocol. This memo describes two 15 closely-related features for TWAMP: an optional capability where the 16 responder host returns some of the command octets or padding octets 17 to the controller, and an optional sender packet format that ensures 18 equal test packet sizes are used in both directions. 20 Requirements Language 22 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 23 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 24 document are to be interpreted as described in RFC 2119 [RFC2119]. 26 Status of this Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at http://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on December 1, 2010. 43 Copyright Notice 45 Copyright (c) 2010 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (http://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 This document may contain material from IETF Documents or IETF 59 Contributions published or made publicly available before November 60 10, 2008. The person(s) controlling the copyright in some of this 61 material may not have granted the IETF Trust the right to allow 62 modifications of such material outside the IETF Standards Process. 63 Without obtaining an adequate license from the person(s) controlling 64 the copyright in such materials, this document may not be modified 65 outside the IETF Standards Process, and derivative works of it may 66 not be created outside the IETF Standards Process, except to format 67 it for publication as an RFC or to translate it into languages other 68 than English. 70 Table of Contents 72 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 73 2. Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . 4 74 3. TWAMP Control Extensions . . . . . . . . . . . . . . . . . . . 5 75 3.1. Connection Setup with New Features . . . . . . . . . . . . 5 76 3.2. Reflect Octets: Request-TW-Session Packet Format . . . . . 6 77 3.3. Reflect Octets: Accept Session Packet Format . . . . . . . 8 78 3.4. Additional considerations . . . . . . . . . . . . . . . . 10 79 4. Extended TWAMP Test . . . . . . . . . . . . . . . . . . . . . 10 80 4.1. Sender Behavior . . . . . . . . . . . . . . . . . . . . . 10 81 4.1.1. Packet Timings . . . . . . . . . . . . . . . . . . . . 10 82 4.1.2. Reflect Octets: Packet Formats and Contents . . . . . 10 83 4.1.3. Reflect Octets: Interaction with Padding Truncation . 12 84 4.1.4. Symmetrical Size: Session-Sender Packet Format . . . . 13 85 4.1.5. Symmetrical Size AND Reflect Octets: 86 Session-Sender Packet Format . . . . . . . . . . . . . 14 87 4.2. Reflector Behavior . . . . . . . . . . . . . . . . . . . . 15 88 4.2.1. Reflect Octets: Session-Reflector Packet Format 89 and Contents . . . . . . . . . . . . . . . . . . . . . 16 90 4.2.2. Symmetrical Size: Session-Reflector Packet Format . . 17 91 4.2.3. Symmetrical Size AND Reflect Octets: 92 Session-Sender Packet Format . . . . . . . . . . . . . 17 93 5. Security Considerations . . . . . . . . . . . . . . . . . . . 17 94 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 95 6.1. Registry Specification . . . . . . . . . . . . . . . . . . 18 96 6.2. Registry Management . . . . . . . . . . . . . . . . . . . 18 97 6.3. Experimental Numbers . . . . . . . . . . . . . . . . . . . 18 98 6.4. Registry Contents . . . . . . . . . . . . . . . . . . . . 18 99 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19 100 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 101 8.1. Normative References . . . . . . . . . . . . . . . . . . . 19 102 8.2. Informative References . . . . . . . . . . . . . . . . . . 20 103 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 105 1. Introduction 107 The IETF has completed its work on the core specification of TWAMP - 108 the Two-Way Active Measurement Protocol [RFC5357]. TWAMP is an 109 extension of the One-way Active Measurement Protocol, OWAMP 110 [RFC4656]. The TWAMP specification gathered wide review as it 111 approached completion, and the by-products were several 112 recommendations for new features in TWAMP. There are a growing 113 number TWAMP implementations at present, and wide-spread usage is 114 expected. There are even devices that are designed to test 115 implementations for protocol compliance. 117 This memo describes two closely-related features for TWAMP. 119 One is the OPTIONAL capability for the responder host to return a 120 limited number of unassigned (padding) octets to the Control-Client 121 or Session-Sender entities in both the TWAMP-Control and TWAMP-Test 122 protocols. With this capability, the Control-Client or Session- 123 Sender can embed octets of information it deems useful and have the 124 assurance that the corresponding reply/test packet will contain that 125 information when it is reflected and returned (by the Server or 126 Session-Reflector. 128 The memo also adds an OPTIONAL capability to assure that reflected 129 test packets are the same size in both directions of transmission. 130 This is accomplished by specifying a new TWAMP-Test Session-Sender 131 packet format. 133 This memo is an update to the TWAMP core protocol specified in 134 [RFC5357]. Measurement systems are not required to implement the 135 features described in this memo to claim compliance with [RFC5357]. 137 Throughout this memo, the bits marked MBZ (Must Be Zero) MUST be set 138 to zero by senders and MUST be ignored by receivers. Also, the HMAC 139 (Hashed Message Authentication Code) MUST be calculated as defined in 140 Section 3.2 of [RFC4656]. 142 2. Purpose and Scope 144 The purpose of this memo is to define two OPTIONAL closely-related 145 features for TWAMP [RFC5357]. The features enhance the TWAMP 146 responder's capabilities to perform simple operations on control and 147 test packets: the reflection of octets or padding and symmetrical 148 sizes of fields in the TWAMP-Test packets. Motivations include 149 permitting the controller host to tag packets with an index for 150 simplified identification, and/or assert that the same size test 151 packets will be used in each direction. 153 The scope of the memo is limited to specifications of the following 154 features: 156 o Reflect Octets: the capability of the Server/Session-Reflector to 157 reflect specific octets back to the Client/Session-Sender. 159 o Symmetrical Size: the capability to ensure that TWAMP-Test 160 protocol uses the same packet size in both directions through 161 support of a new TWAMP-Test Session-Sender test packet format in 162 both the Session-Sender and the Session-Reflector. Only the 163 Session-Sender test packet format is new. 165 This memo extends the modes of operation through assignment of two 166 new values in the Modes Field (see section 3.1 of[RFC4656] for the 167 format of the Server Greeting message), while retaining backward 168 compatibility with the core TWAMP [RFC5357] implementations. The two 169 new values correspond to the two features defined in this memo. 171 When the Server and Control-Client have agreed to use the Reflect 172 Octets mode during control connection setup, then the Control-Client, 173 the Server, the Session-Sender, and the Session-Reflector MUST all 174 conform to the requirements of that mode, as identified below. 176 When the Server and Control-Client have agreed to use the Symmetrical 177 Size mode during control connection setup, then the Control-Client, 178 the Server, the Session-Sender, and the Session-Reflector MUST all 179 conform to the requirements of that mode, as identified below. 181 3. TWAMP Control Extensions 183 TWAMP-Control protocol [RFC5357] uses the Modes Field to identify and 184 select specific communication capabilities, and this field is a 185 recognized extension mechanism. The following sections describe two 186 such extensions. 188 3.1. Connection Setup with New Features 190 TWAMP connection establishment follows the procedure defined in 191 section 3.1 of [RFC4656] and section 3.1 of [RFC5357]. The new 192 features require two new bit positions (and values) to identify the 193 ability of the Server/Session-Reflector to reflect specific octets 194 back to the Control-Client/Session-Sender, and to support the new 195 Session-Sender packet format in TWAMP-Test Protocol. With this added 196 feature, the complete set of TWAMP Modes Field bit positions and 197 values would be as follows: 199 Value Description Reference/Explanation 200 0 Reserved 201 1 Unauthenticated RFC4656, Section 3.1 202 2 Authenticated RFC4656, Section 3.1 203 4 Encrypted RFC4656, Section 3.1 204 8 Unauth. TEST protocol, RFC5681, Section 3.1 205 Encrypted CONTROL 206 16 Individual Session RFC????, Section 3.1 207 Control 208 -------------------------------------------------------- 209 xxx Reflect Octets new bit position (X) 210 Capability 211 yyy Symmetrical Size new bit position (Y) 212 Sender Test Packet Format 214 In the original OWAMP Modes Field, setting bit positions 0, 1 or 2 215 indicated the security mode of the Control protocol, and the Test 216 protocol inherited the same mode (see section 4 of [RFC4656]). In 217 [RFC5618], bit position 3 allows unauthenticated TWAMP Test protocol 218 to be used with encryption on the TWAMP-Control protocol in a mixed 219 mode of operation. 221 The Server sets one or both of the new bit positions (X and Y) in the 222 Modes Field of the Server Greeting message to indicate its 223 capabilities and willingness to operate in either of these modes (or 224 both) if desired. 226 >>>IANA: change xxx, yyy, X, Y, and RFC???? to the assigned values 227 <<< 229 If the Control-Client intends to operate all test sessions invoked 230 with this control connection using one or both of the new modes, it 231 MUST set the Mode Field bit corresponding to each function in the 232 Setup Response message. With this and other extensions, the Control- 233 Client MAY set multiple Mode Field bits in the Setup Response 234 message. 236 3.2. Reflect Octets: Request-TW-Session Packet Format 238 The bits designated for the Reflect Octets feature in the Request-TW- 239 Session command are as shown in the packet format below. 241 0 1 2 3 242 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 244 | 5 | MBZ | IPVN | Conf-Sender | Conf-Receiver | 245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 246 | Number of Schedule Slots | 247 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 248 . . 249 . ... Many fields (66 octets) not shown ... . 250 . . 251 . . 252 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 253 | Padding Length (4 octets) | 254 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 255 | Start Time, (8 octets) | 256 | | 257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 258 | Timeout, (8 octets) | 259 | | 260 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 261 | Type-P Descriptor | 262 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 263 | Octets to be reflected | Length of padding to reflect | 264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 265 | MBZ (4 octets) | 266 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 267 | | 268 | HMAC (16 octets) | 269 | | 270 | | 271 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 273 The "Padding Length" Field *continues* to specify the number of 274 padding octets that the Session-Sender will append to ALL TWAMP-Test 275 packets associated with this test session. See below for 276 considerations on the minimum length of the padding octets, following 277 the definitions of the two new fields that follow the Type-P 278 Descriptor. 280 Note that the number of padding octets appended to the Session- 281 Reflector's test packet depends on support for the RECOMMENDED 282 truncation process in TWAMP section 4.2.1 [RFC5357]. 284 The "Octets to be reflected" Field SHALL be 2 octets long, as shown 285 and contains the octets that the Server MUST reflect in the Accept 286 Session message as specified below. 288 The "Length of padding to reflect" Field SHALL be 2 octets long, and 289 contain an unsigned binary value in units of octets. This field 290 communicates the length of the padding in the TWAMP-Test Packet that 291 the Session-Sender expects to be reflected, and the length of octets 292 that the Session-Reflector SHALL return in include in its TWAMP-Test 293 packet format (see section 4.2). By including this length field in 294 the Request-TW-Session message, a Server is able to determine if it 295 can comply with a specific request to reflect padding in the TWAMP- 296 Test packets, and to arrange for the Session-Reflector processing in 297 advance. 299 The "Padding Length" SHOULD be >= 27 octets when specifying a test 300 session using the Unauthenticated TWAMP-Test mode, to allow for the 301 RECOMMENDED truncation process in TWAMP section 4.2.1 [RFC5357]. 303 The "Padding Length" SHOULD be >= 56 octets when specifying a test 304 session using the Authenticated or Encrypted TWAMP-Test modes, to 305 allow for the RECOMMENDED truncation process in TWAMP section 4.2.1 306 [RFC5357]. 308 The "Padding Length" SHALL be > the "Length of padding to reflect" 309 when specifying a test session using the OPTIONAL Reflect Octets 310 mode. 312 In Unauthenticated TWAMP-Test mode, the "Padding Length" SHALL be >= 313 27 + "Length of padding to reflect" octets when specifying a test 314 session using BOTH the OPTIONAL Reflect Octets mode and the 315 RECOMMENDED truncation process in TWAMP section 4.2.1 [RFC5357]. 317 In Authenticated or Encrypted TWAMP-Test modes, the "Padding Length" 318 SHALL be >= 56 + "Length of padding to reflect" octets when 319 specifying a test session using BOTH the OPTIONAL Reflect Octets mode 320 and the RECOMMENDED truncation process in TWAMP section 4.2.1 321 [RFC5357]. 323 3.3. Reflect Octets: Accept Session Packet Format 325 The bits designated for the Reflect Padding feature in the Accept 326 Session command are as shown in the packet format below. 328 0 1 2 3 329 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 331 | Accept | MBZ | Port | 332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 333 | | 334 | SID (16 octets) | 335 | | 336 | | 337 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 338 | Reflected octets | Server octets | 339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 340 | MBZ (8 octets) | 341 | | 342 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 343 | | 344 | HMAC (16 octets) | 345 | | 346 | | 347 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 349 The "Reflected octets" field SHALL contain the octets from the 350 Request-TW-Session "Octets to be reflected" Field, and be 2 octets 351 long, as shown. 353 The "Server octets" field SHALL contain information that the Server 354 intends to be returned in the TWAMP-Test packet padding to-be- 355 reflected Field, OR SHALL be zero, and be 2 octets long, as shown. 356 Although the Server determines the SID, this field is very long (16 357 octets) and does not normally appear in TWAMP-Test packets. The 358 following items MUST be part of compliant implementations using the 359 Reflect Octets feature: 361 o When a Server does not require octets to be returned in TWAMP-Test 362 packets, it MUST send all zeros in the Server octets field 364 o When a Server intends octets to be returned in TWAMP-Test packets, 365 it MUST send a non-zero value in the Server octets field, and the 366 TWAMP-Test Sender MUST include those octets at the beginning of 367 the "Packet Padding (to be reflected)" field 369 o Section 4.1.2 defines how Server octets MUST be included in the 370 TWAMP-Test packet padding when this service is desired by the 371 Server (indicated in the second of two figures in the section) 373 When supporting the RECOMMENDED truncation process in TWAMP section 374 4.2.1 [RFC5357], IF calculations on the Padding lengths reveal that 375 there are insufficient octets supplied to produce equal-length 376 Session-Sender and Session-Reflector test packets, then the Accept 377 Field MUST be set to 3 = some aspect of the request is not supported. 379 3.4. Additional considerations 381 The value of the Modes Field sent by the Server in the Server 382 Greeting message is the bit-wise OR of the mode values that it is 383 willing to support during this session. 385 With the publication of this memo as an RFC, the last 7 bit positions 386 of the Modes 32-bit Field are used. A Control-Client conforming to 387 this extension of [RFC5357] MAY ignore the values in the higher bits 388 of the Modes Field, or it MAY support other features that are 389 communicated in those bit positions. The other bits are available 390 for future protocol extensions. 392 4. Extended TWAMP Test 394 The TWAMP test protocol is similar to the OWAMP [RFC4656] test 395 protocol with the exception that the Session-Reflector transmits test 396 packets to the Session-Sender in response to each test packet it 397 receives. TWAMP section 4[RFC5357] defines two additional test 398 packet formats for packets transmitted by the Session-Reflector. The 399 appropriate format depends on the security mode chosen. The new 400 modes specified here utilize some of the padding octets within each 401 test packet format, or require truncation of those octets depending 402 on the security mode in use. 404 4.1. Sender Behavior 406 This section describes extensions to the behavior of the TWAMP 407 Session-Sender. 409 4.1.1. Packet Timings 411 The Send Schedule is not utilized in TWAMP, and this is unchanged in 412 this memo. 414 4.1.2. Reflect Octets: Packet Formats and Contents 416 The Session-Sender packet format and content follow the same 417 procedure and guidelines as defined in section 4.1.2 of [RFC4656] (as 418 indicated in section 4.1.2 of TWAMP [RFC5357]). 420 The Reflect octets mode re-designates the original TWAMP-Test (and 421 OWAMP-Test) Packet Padding Field (see section 4.1.2 of [RFC4656]), as 422 shown below for unauthenticated mode: 424 0 1 2 3 425 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 426 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 427 | Sequence Number | 428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 429 | Timestamp | 430 | | 431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 432 | Error Estimate | | 433 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 434 | | 435 | Packet Padding (to be reflected) | 436 . (length in octets specified in command) . 437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 438 . . 439 . Additional Packet Padding . 440 . . 441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 443 The "Packet Padding (to be reflected)" Field SHALL correspond to the 444 length of octets specified in the Request-TW-Session "Length of 445 padding to reflect" Field to this test session. These are the octets 446 that the Session-Sender expects will be returned by the Session- 447 Reflector. 449 The length of the "Additional Packet Padding" Field is the difference 450 between two fields in the Request-TW-Session command, as follows: 452 "Additional Packet Padding", in octets = 454 "Padding Length" - "Length of padding to reflect" 456 When a Server intends octets to be returned in TWAMP-Test packets, it 457 MUST send a non-zero value in the Server octets field, and the TWAMP- 458 Test Session-Sender MUST include those octets in the first 2 octets 459 of the "Packet Padding (to be reflected)" Field as shown below: 461 0 1 2 3 462 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 463 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 464 | Server octets | 465 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 466 | | 467 | Packet Padding (to be reflected) | 468 . (length in octets specified elsewhere) . 469 . . 470 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 472 The "Server octets" field contains the same information that the 473 Server returned to the Control-Client in the Accept-Session message 474 corresponding to this specific test session (see section 3.3). At 475 the Session-Reflector, these octets MUST be reflected the same as the 476 rest of the "Packet Padding (to be reflected)" field. 478 Note that it is permissible for the Session-Sender to insert the same 479 octets used in the "Octets to be reflected" field of the Request-TW- 480 Session command elsewhere in the "Packet Padding (to be reflected)" 481 field. 483 4.1.3. Reflect Octets: Interaction with Padding Truncation 485 When the Reflect Octets mode is selected, and the RECOMMENDED 486 truncation process in TWAMP section 4.2.1 [RFC5357] is supported, the 487 Session-Sender MUST anticipate a minimum padding required to achieve 488 equal size test packets in both directions. The amount of padding 489 needed to achieve symmetrical packet size depends on BOTH the 490 security mode (Unauthenticated/Authenticated/Encrypted) and whether 491 the Reflect Octets mode is selected simultaneously. 493 When using the RECOMMENDED truncation process in TWAMP section 4.2.1 494 [RFC5357] alone, the Session-Sender MUST append sufficient Packet 495 Padding octets to allow the same IP packet payload lengths to be used 496 in each direction of transmission (this is usually desirable). To 497 compensate for the Session-Reflector's larger test packet format, the 498 Session-Sender MUST append at least 27 octets of padding in 499 Unauthenticated mode, and at least 56 octets in Authenticated and 500 Encrypted modes. The sizes of TWAMP Test protocol packets and the 501 resulting truncated padding to achieve equal packet sizes in both 502 directions are shown in the table below: 504 +-------------------+----------------------+---------------------+ 505 | Octets in: | Unauthenticated Mode | Auth/Encrypted Mode | 506 +-------------------+----------------------+---------------------+ 507 | Reflector Header | 41 | 104 | 508 | Sender Header | 14 | 48 | 509 | Truncated Padding | 27 | 56 | 510 +-------------------+----------------------+---------------------+ 512 TWAMP-Test Padding Trucation 514 When using the Reflect Octets mode simultaneously with the 515 RECOMMENDED truncation process in TWAMP section 4.2.1 [RFC5357], the 516 Session-Sender MUST append at least 27 octets of padding plus the 517 "Length of the padding to reflect" octets when operating in 518 Unauthenticated mode. The Session-Sender MUST append at least 56 519 octets of padding plus the "Length of the padding to reflect" octets 520 when operating in Authenticated and Encrypted modes. 522 4.1.4. Symmetrical Size: Session-Sender Packet Format 524 When the Symmetrical Size mode is selected, the Session-Sender SHALL 525 use the following TWAMP-Test Packet Format in Unauthenticated mode: 527 Unauthenticated Mode 528 0 1 2 3 529 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 530 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 531 | Sequence Number | 532 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 533 | Timestamp | 534 | | 535 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 536 | Error Estimate | | 537 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 538 | | 539 | | 540 | MBZ (27 octets) | 541 | | 542 | | 543 | | 544 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 545 | | | 546 +-+-+-+-+-+-+-+-+ + 547 . . 548 . Packet Padding . 549 . . 550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 552 This feature REQUIRES only a new Session-Sender test packet format, 553 the Session-Reflector test packet format is unchanged. 555 4.1.5. Symmetrical Size AND Reflect Octets: Session-Sender Packet 556 Format 558 When BOTH the Symmetrical Size mode and the Reflect Octets mode are 559 selected, the Session-Sender SHALL use the following TWAMP-Test 560 Packet Format in Unauthenticated mode: 562 Unauthenticated Mode 563 0 1 2 3 564 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 565 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 566 | Sequence Number | 567 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 568 | Timestamp | 569 | | 570 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 571 | Error Estimate | | 572 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 573 | | 574 | | 575 | MBZ (27 octets) | 576 | | 577 | | 578 | | 579 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 580 | | | 581 +-+-+-+-+-+-+-+-+ + 582 | Packet Padding (to be reflected) | 583 . (length in octets specified in command) . 584 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 585 . . 586 . Additional Packet Padding . 587 . . 588 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 590 In this combined mode, the Packet Padding to be reflected follows the 591 27 MBZ octets. In Authenticated or Encrypted modes, the Packet 592 Padding to be reflected follows the 56 MBZ octets. 594 4.2. Reflector Behavior 596 The TWAMP Reflector follows the procedures and guidelines in section 597 4.2 of [RFC5357], with the following additional functions: 599 o Reflect Octets mode: Designated octets in the "Packet Padding (to 600 be reflected)" field of the Session-Sender's test packet MUST be 601 included in the Session-Reflector's test packet. 603 o Symmetrical Size mode: The Session-Reflector MUST operate using 604 the Session_Reflector Packet Format defined in section 4.1.4, 605 where the Padding Octets are separated from the information 606 fields. 608 4.2.1. Reflect Octets: Session-Reflector Packet Format and Contents 610 The Reflect Padding feature re-designates the packet padding field, 611 as shown below. When the Reflect Octets mode is selected, the 612 Session-Sender SHALL use the following TWAMP-Test Packet Format in 613 Unauthenticated mode: 615 0 1 2 3 616 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 617 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 618 | Sequence Number | 619 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 620 | Timestamp | 621 | | 622 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 623 | Error Estimate | MBZ | 624 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 625 | Receive Timestamp | 626 | | 627 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 628 | Sender Sequence Number | 629 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 630 | Sender Timestamp | 631 | | 632 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 633 | Sender Error Estimate | MBZ | 634 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 635 | Sender TTL | Packet Padding (from Session-Sender) | 636 +-+-+-+-+-+-+-+-+ + 637 . . 638 + +-+-+-+-+-+-+-+-+ 639 | Packet Padding (from Session-Sender) | | 640 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 641 | | 642 | | 643 . Additional Packet Padding . 644 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 645 The "Packet Padding (from Session-Sender)" field MUST be the same 646 octets as the "Packet Padding (to be reflected)" field in the 647 Session-Sender's test packet, and therefore MUST conform to the 648 length specified in the Request-TW-Session message. 650 When the Server has returned a non-zero value in the "Server octets" 651 field of the Accept Session message (as described in section 3.3), 652 then the Session-Reflector SHALL reflect these octets the same as the 653 rest of the "Packet Padding (to be reflected)" Field. 655 When simultaneously using the RECOMMENDED truncation process in TWAMP 656 section 4.2.1 [RFC5357] AND Reflect octets mode, the Session- 657 Reflector MUST reflect the designated octets from the Session- 658 Sender's test packet in the "Packet Padding (from Session-Sender)" 659 Field, and MAY re-use additional Packet Padding from the Session- 660 Sender. The Session-Reflector MUST truncate the padding such that 661 the highest number octets are discarded, and the test packet length 662 equals the Session-Sender's packet length. When using the 663 RECOMMENDED truncation process, the Session-Reflector MUST truncate 664 exactly 27 octets of padding in Unauthenticated mode, and exactly 56 665 octets in Authenticated and Encrypted modes. 667 The Session-Reflector MAY re-use the Sender's Packet Padding (since 668 the requirements for padding generation are the same for each). 670 4.2.2. Symmetrical Size: Session-Reflector Packet Format 672 When Symmetrical Size mode is selected, the Session-Sender packet 673 formats for unauthenticated and authenticated/encrypted modes are 674 identical to the core TWAMP specification, section 4.2.1 of 675 [RFC5357]. Thus, the Session-Reflector test packet format is 676 unchanged. 678 The Session-Reflector MUST construct its test packet using the 679 information in the Session-Sender's test packet. The length of the 680 Session-Reflector's test packet SHALL equal the length of the 681 Session-Sender's test packet. 683 4.2.3. Symmetrical Size AND Reflect Octets: Session-Sender Packet 684 Format 686 When BOTH the Symmetrical Size mode and the Reflect Octets mode are 687 selected, the Session-Reflector MUST operate using the 688 Session_Reflector Packet Format defined in section 4.1.5, where the 689 Padding Octets are separated from the information fields, and the 690 Padding to be Reflected field precedes the Additional Padding. 692 The Session-Reflector SHALL use the same TWAMP-Test Packet Format as 693 specified in section 4.2.1 above. 695 5. Security Considerations 697 These extended modes of operation do not appear to permit any new 698 attacks on hosts communicating with core TWAMP [RFC5357]. 700 The security considerations that apply to any active measurement of 701 live networks are relevant here as well. See [RFC4656] and 702 [RFC5357]. 704 6. IANA Considerations 706 This memo adds two modes to the IANA registry for the TWAMP Modes 707 Field, and describes behavior when the new modes are used. This 708 field is a recognized extension mechanism for TWAMP. 710 6.1. Registry Specification 712 IANA has created a TWAMP-Modes registry (as requested in [RFC5618]). 713 TWAMP-Modes are specified in TWAMP Server Greeting messages and 714 Set-up Response messages, as described in section 3.1 of [RFC5357], 715 consistent with section 3.1 of [RFC4656], and extended by this memo. 716 Modes are indicated by setting bits in the 32-bit Modes field that 717 correspond to values in the Modes registry. For the TWAMP-Modes 718 registry, we expect that new features will be assigned increasing 719 registry values that correspond to single bit positions, unless there 720 is a good reason to do otherwise (more complex encoding than single 721 bit positions may be used in the future, to access the 2^32 value 722 space). 724 6.2. Registry Management 726 This registry must be updated only by "IETF Consensus" as specified 727 in [RFC5226](an RFC documenting registry use that is approved by the 728 IESG). 730 6.3. Experimental Numbers 732 No experimental values are currently assigned for the Modes Registry. 734 6.4. Registry Contents 736 TWAMP Modes Registry is recommended to be augmented as follows: 738 Value Description Semantics Definition 739 0 Reserved 741 1 Unauthenticated RFC4656, Section 3.1 743 2 Authenticated RFC4656, Section 3.1 745 4 Encrypted RFC4656, Section 3.1 747 8 Unauth. TEST protocol, RFC5618, Section 3.1 (3) 748 Auth. CONTROL 749 16 Individual Session RFC????, Section 3.1 750 Control bit position (4) 751 -------------------------------------------------------- 752 xxx Reflect Octets this memo, section 3.1 753 Capability new bit position (X) 754 yyy Symmetrical Size this memo, section 3.1 755 Sender Test Packet Format new bit position (Y) 757 The suggested values are 759 X=5, xxx=32 761 Y=6, yyy=64 763 7. Acknowledgements 765 The authors thank Steve Baillargeon, Walt Steverson, and Stina Ross 766 for helpful review and comments. 768 8. References 770 8.1. Normative References 772 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 773 Requirement Levels", BCP 14, RFC 2119, March 1997. 775 [RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. 776 Zekauskas, "A One-way Active Measurement Protocol 777 (OWAMP)", RFC 4656, September 2006. 779 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 780 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 781 May 2008. 783 [RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. 784 Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)", 785 RFC 5357, October 2008. 787 [RFC5618] Morton, A. and K. Hedayat, "Mixed Security Mode for the 788 Two-Way Active Measurement Protocol (TWAMP)", RFC 5618, 789 August 2009. 791 8.2. Informative References 793 Authors' Addresses 795 Al Morton 796 AT&T Labs 797 200 Laurel Avenue South 798 Middletown,, NJ 07748 799 USA 801 Phone: +1 732 420 1571 802 Fax: +1 732 368 1192 803 Email: acmorton@att.com 804 URI: http://home.comcast.net/~acmacm/ 806 Len Ciavattone 807 AT&T Labs 808 200 Laurel Avenue South 809 Middletown,, NJ 07748 810 USA 812 Phone: +1 732 420 1239 813 Fax: 814 Email: lencia@att.com 815 URI: