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Ciavattone 4 Updates: 5357 (if approved) AT&T Labs 5 Intended status: Standards Track August 17, 2010 6 Expires: February 18, 2011 8 TWAMP Reflect Octets and Symmetrical Size Features 9 draft-ietf-ippm-twamp-reflect-octets-09 11 Abstract 13 This memo describes two closely-related features for the core 14 specification of TWAMP - the Two-Way Active Measurement Protocol: an 15 optional capability where the responding host returns some of the 16 command octets or padding octets to the sender, and an optional 17 sender packet format that ensures equal test packet sizes are used in 18 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 February 18, 2011. 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 Contents . . . . . . . . . . . . . . . . . . . . 18 97 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18 98 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 99 8.1. Normative References . . . . . . . . . . . . . . . . . . . 19 100 8.2. Informative References . . . . . . . . . . . . . . . . . . 19 101 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 103 1. Introduction 105 TWAMP - the Two-Way Active Measurement Protocol [RFC5357] is an 106 extension of the One-way Active Measurement Protocol, OWAMP 107 [RFC4656]. The TWAMP specification gathered wide review as it 108 approached completion, and the by-products were several 109 recommendations for new features in TWAMP. 111 This memo describes two closely-related features for TWAMP. 113 One is the OPTIONAL capability for the responder host to return a 114 limited number of unassigned (padding) octets to the Control-Client 115 or Session-Sender entities in both the TWAMP-Control and TWAMP-Test 116 protocols. With this capability, the Control-Client or Session- 117 Sender can embed octets of information it deems useful and have the 118 assurance that the corresponding reply/test packet will contain that 119 information when it is reflected and returned (by the Server or 120 Session-Reflector). 122 The memo also adds an OPTIONAL capability to assure that reflected 123 test packets are the same size in both directions of transmission. 124 This is accomplished by specifying a new TWAMP-Test Session-Sender 125 packet format. Although TWAMP [RFC5357] recommends padding 126 truncation to achieve symmetrical sizes (to compensate for the 127 Session-Reflector's larger test packet header), it's not guaranteed 128 that the Session-Reflector will truncate the padding, and it's not 129 possible if there's insufficient padding. 131 This memo is an update to the TWAMP core protocol specified in 132 [RFC5357]. Measurement systems are not required to implement the 133 features described in this memo to claim compliance with [RFC5357]. 135 Throughout this memo, the bits marked MBZ (Must Be Zero) MUST be set 136 to zero by senders and MUST be ignored by receivers. Also, the HMAC 137 (Hashed Message Authentication Code) MUST be calculated as defined in 138 Section 3.2 of [RFC4656]. 140 2. Purpose and Scope 142 The purpose of this memo is to define two OPTIONAL closely-related 143 features for TWAMP [RFC5357]. The features enhance the TWAMP host's 144 capabilities to perform a simple operation on control and test 145 packets: the reflection of octets or padding, and the capability to 146 ensure symmetrical size TWAMP-Test packets. Motivations include 147 permitting the controller host to tag packets with an index for 148 simplified identification, and/or assert that the same size test 149 packets will be used in each direction. 151 The scope of the memo is limited to specifications of the following 152 features: 154 o Reflect Octets: the capability of the Server/Session-Reflector to 155 reflect specific octets back to the Client/Session-Sender, and a 156 similar service provided by the Client and Session-Sender. 158 o Symmetrical Size: the capability to ensure that TWAMP-Test 159 protocol uses the same packet size in both directions through 160 support of a new TWAMP-Test Session-Sender test packet format in 161 both the Session-Sender and the Session-Reflector. Only the 162 Session-Sender test packet format is new. 164 This memo extends the modes of operation through assignment of two 165 new values in the Modes Field (see section 3.1 of[RFC4656] for the 166 format of the Server Greeting message), while retaining backward 167 compatibility with the core TWAMP [RFC5357] implementations. The two 168 new values correspond to the two features defined in this memo. 170 When the Server and Control-Client have agreed to use the Reflect 171 Octets mode during control connection setup, then the Control-Client, 172 the Server, the Session-Sender, and the Session-Reflector MUST all 173 conform to the requirements of that mode, as identified below. 175 When the Server and Control-Client have agreed to use the Symmetrical 176 Size mode during control connection setup, then the Control-Client, 177 the Server, the Session-Sender, and the Session-Reflector MUST all 178 conform to the requirements of that mode, as identified below. 180 3. TWAMP Control Extensions 182 TWAMP-Control protocol [RFC5357] uses the Modes Field to identify and 183 select specific communication capabilities, and this field is a 184 recognized extension mechanism. The following sections describe two 185 such extensions. 187 3.1. Connection Setup with New Features 189 TWAMP connection establishment follows the procedure defined in 190 section 3.1 of [RFC4656] and section 3.1 of [RFC5357]. The new 191 features require two new bit positions (and values) to identify the 192 ability of the Server/Session-Reflector to reflect specific octets 193 back to the Control-Client/Session-Sender, and to support the new 194 Session-Sender packet format in TWAMP-Test Protocol. See the IANA 195 section for details on the assigned values and bit positions. 197 The Server sets one or both of the new bit positions in the Modes 198 Field of the Server Greeting message to indicate its capabilities and 199 willingness to operate in either of these modes (or both) if desired. 201 If the Control-Client intends to operate all test sessions invoked 202 with this control connection using one or both of the new modes, it 203 MUST set the Mode Field bit corresponding to each function in the 204 Setup Response message. With this and other extensions, the Control- 205 Client MAY set multiple Mode Field bits in the Setup Response 206 message. 208 3.2. Reflect Octets: Request-TW-Session Packet Format 210 The bits designated for the Reflect Octets feature in the Request-TW- 211 Session command are as shown in the packet format below. 213 0 1 2 3 214 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 1 215 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 216 | 5 | MBZ | IPVN | Conf-Sender | Conf-Receiver | 217 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 218 | Number of Schedule Slots | 219 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 220 . . 221 . ... Many fields (66 octets) not shown ... . 222 . . 223 . . 224 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 225 | Padding Length (4 octets) | 226 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 227 | Start Time, (8 octets) | 228 | | 229 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 230 | Timeout, (8 octets) | 231 | | 232 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 233 | Type-P Descriptor | 234 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 235 | Octets to be reflected | Length of padding to reflect | 236 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 237 | MBZ (4 octets) | 238 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 239 | | 240 | HMAC (16 octets) | 241 | | 242 | | 243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 245 It is important to note that the "Padding Length" Field continues to 246 specify the number of padding octets that the Session-Sender will 247 append to ALL TWAMP-Test packets associated with this test session. 248 See below for considerations on the minimum length of the padding 249 octets, following the definitions of the two new fields that follow 250 the Type-P Descriptor. 252 Note that the number of padding octets appended to the Session- 253 Reflector's test packet depends on support for the truncation process 254 that TWAMP section 4.2.1 [RFC5357] recommends. 256 The "Octets to be reflected" Field SHALL be 2 octets long, as shown 257 and contains the octets that the Server MUST reflect in the Accept 258 Session message as specified below. 260 The "Length of padding to reflect" Field SHALL be 2 octets long, and 261 contain an unsigned binary value in units of octets. This field 262 communicates the length of the padding in the TWAMP-Test Packet that 263 the Session-Sender expects to be reflected, and the length of octets 264 that the Session-Reflector SHALL return in its TWAMP-Test packet 265 format (see section 4.2). By including this length field in the 266 Request-TW-Session message, a Server is able to determine if it can 267 comply with a specific request to reflect padding in the TWAMP-Test 268 packets, and to arrange for the Session-Reflector processing in 269 advance. 271 The "Padding Length" SHOULD be >= 27 octets when specifying a test 272 session using the Unauthenticated TWAMP-Test mode, to allow for the 273 truncation process that TWAMP section 4.2.1 [RFC5357] recommends. 275 The "Padding Length" SHOULD be >= 56 octets when specifying a test 276 session using the Authenticated or Encrypted TWAMP-Test modes, to 277 allow for the truncation process that TWAMP section 4.2.1 [RFC5357] 278 recommends. 280 The "Padding Length" SHALL be > the "Length of padding to reflect" 281 when specifying a test session using the OPTIONAL Reflect Octets 282 mode. 284 In Unauthenticated TWAMP-Test mode, the "Padding Length" SHALL be >= 285 27 + "Length of padding to reflect" octets when specifying a test 286 session using both the OPTIONAL Reflect Octets mode and the 287 truncation process that TWAMP section 4.2.1 [RFC5357] recommends. 289 In Authenticated or Encrypted TWAMP-Test modes, the "Padding Length" 290 SHALL be >= 56 + "Length of padding to reflect" octets when 291 specifying a test session using both the OPTIONAL Reflect Octets mode 292 and the truncation process that TWAMP section 4.2.1 [RFC5357] 293 recommends. 295 3.3. Reflect Octets: Accept Session Packet Format 297 The bits designated for the Reflect Padding feature in the Accept 298 Session command are as shown in the packet format below. 300 0 1 2 3 301 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 1 302 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 303 | Accept | MBZ | Port | 304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 305 | | 306 | SID (16 octets) | 307 | | 308 | | 309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 310 | Reflected octets | Server octets | 311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 312 | MBZ (8 octets) | 313 | | 314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 315 | | 316 | HMAC (16 octets) | 317 | | 318 | | 319 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 321 The "Reflected octets" field SHALL contain the octets from the 322 Request-TW-Session "Octets to be reflected" Field, and be 2 octets 323 long, as shown. 325 The "Server octets" field SHALL contain information that the Server 326 intends to be returned in the TWAMP-Test packet padding to-be- 327 reflected Field, OR SHALL be zero, and be 2 octets long, as shown. 328 Although the Server determines the SID, this field is very long (16 329 octets) and does not normally appear in TWAMP-Test packets. The 330 following items MUST be part of compliant implementations using the 331 Reflect Octets feature: 333 o When a Server does not require octets to be returned in TWAMP-Test 334 packets, it MUST send all zeros in the Server octets field 336 o When a Server intends octets to be returned in TWAMP-Test packets, 337 it MUST send a non-zero value in the Server octets field, and the 338 TWAMP-Test Sender MUST include those octets at the beginning of 339 the "Packet Padding (to be reflected)" field 341 o Section 4.1.2 defines how Server octets MUST be included in the 342 TWAMP-Test packet padding when this service is desired by the 343 Server (indicated in the second of two figures in the section) 345 When performing the truncation process that TWAMP section 4.2.1 346 [RFC5357] recommends, if calculations on the Padding lengths reveal 347 that there are insufficient octets supplied to produce equal-length 348 Session-Sender and Session-Reflector test packets, then the Accept 349 Field MUST be set to 3 to indicate that some aspect of the request is 350 not supported. 352 3.4. Additional considerations 354 The value of the Modes Field sent by the Server in the Server 355 Greeting message is the bit-wise OR of the mode values that it is 356 willing to support during this session. 358 With the publication of this memo as an RFC, the last 7 bit positions 359 of the Modes 32-bit Field are used. A Control-Client conforming to 360 this extension of [RFC5357] MAY ignore the values in the higher bits 361 of the Modes Field, or it MAY support other features that are 362 communicated in those bit positions. The other bits are available 363 for future protocol extensions. 365 4. Extended TWAMP Test 367 The TWAMP test protocol is similar to the OWAMP [RFC4656] test 368 protocol with the exception that the Session-Reflector transmits test 369 packets to the Session-Sender in response to each test packet it 370 receives. TWAMP section 4[RFC5357] defines two additional test 371 packet formats for packets transmitted by the Session-Reflector. The 372 appropriate format depends on the security mode chosen. The new 373 modes specified here utilize some of the padding octets within each 374 test packet format, or require truncation of those octets depending 375 on the security mode in use. 377 4.1. Sender Behavior 379 This section describes extensions to the behavior of the TWAMP 380 Session-Sender. 382 4.1.1. Packet Timings 384 The Send Schedule is not utilized in TWAMP, and this is unchanged in 385 this memo. 387 4.1.2. Reflect Octets: Packet Formats and Contents 389 The Session-Sender packet format and content follow the same 390 procedure and guidelines as defined in section 4.1.2 of [RFC4656] (as 391 indicated in section 4.1.2 of TWAMP [RFC5357]). 393 The Reflect octets mode re-designates the original TWAMP-Test Packet 394 Padding Field (see section 4.1.2 of [RFC4656]), as shown below for 395 unauthenticated mode: 397 0 1 2 3 398 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 1 399 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 400 | Sequence Number | 401 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 402 | Timestamp | 403 | | 404 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 405 | Error Estimate | | 406 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 407 | | 408 | Packet Padding (to be reflected) | 409 . (length in octets specified in command) . 410 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 411 . . 412 . Additional Packet Padding . 413 . . 414 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 416 The "Packet Padding (to be reflected)" Field SHALL correspond to the 417 length of octets specified in the Request-TW-Session "Length of 418 padding to reflect" Field to this test session. These are the octets 419 that the Session-Sender expects will be returned by the Session- 420 Reflector. 422 The length of the "Additional Packet Padding" Field is the difference 423 between two fields in the Request-TW-Session command, as follows: 425 "Additional Packet Padding", in octets = 427 "Padding Length" - "Length of padding to reflect" 429 When a Server intends octets to be returned in TWAMP-Test packets, it 430 MUST send a non-zero value in the Server octets field, and the TWAMP- 431 Test Session-Sender MUST include those octets in the first 2 octets 432 of the "Packet Padding (to be reflected)" Field as shown below: 434 0 1 2 3 435 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 1 436 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 437 | Server octets | 438 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 439 | | 440 | Remaining Packet Padding (to be reflected) | 441 . (total length in octets specified in command) . 442 . . 443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 445 The "Server octets" field contains the same information that the 446 Server returned to the Control-Client in the Accept-Session message 447 corresponding to this specific test session (see section 3.3). At 448 the Session-Reflector, these octets MUST be reflected the same as the 449 rest of the "Packet Padding (to be reflected)" field. 451 Note that it is permissible for the Session-Sender to insert the same 452 octets used in the "Octets to be reflected" field of the Request-TW- 453 Session command elsewhere in the "Packet Padding (to be reflected)" 454 field. 456 4.1.3. Reflect Octets: Interaction with Padding Truncation 458 When the Reflect Octets mode is selected, and the performing 459 truncation process that TWAMP section 4.2.1 [RFC5357] recommends, the 460 Session-Sender MUST anticipate a minimum padding required to achieve 461 equal size test packets in both directions. The amount of padding 462 needed to achieve symmetrical packet size depends on both the 463 security mode (Unauthenticated/Authenticated/Encrypted) and whether 464 the Reflect Octets mode is selected simultaneously. 466 When using the truncation process in TWAMP section 4.2.1 [RFC5357] 467 alone, the Session-Sender MUST append sufficient Packet Padding 468 octets to allow the same IP packet payload lengths to be used in each 469 direction of transmission (this is usually desirable). To compensate 470 for the Session-Reflector's larger test packet format, the Session- 471 Sender MUST append at least 27 octets of padding in Unauthenticated 472 mode, and at least 56 octets in Authenticated and Encrypted modes. 473 The sizes of TWAMP Test protocol packets and the resulting truncated 474 padding to achieve equal packet sizes in both directions are shown in 475 the table below: 477 +-------------------+----------------------+---------------------+ 478 | Octets in: | Unauthenticated Mode | Auth/Encrypted Mode | 479 +-------------------+----------------------+---------------------+ 480 | Reflector Header | 41 | 104 | 481 | Sender Header | 14 | 48 | 482 | Truncated Padding | 27 | 56 | 483 +-------------------+----------------------+---------------------+ 485 TWAMP-Test Padding Truncation 487 When using the Reflect Octets mode simultaneously with the truncation 488 process that TWAMP recommends in section 4.2.1 [RFC5357], the 489 Session-Sender MUST append at least 27 octets of padding plus the 490 "Length of the padding to reflect" octets when operating in 491 Unauthenticated mode. The Session-Sender MUST append at least 56 492 octets of padding plus the "Length of the padding to reflect" octets 493 when operating in Authenticated and Encrypted modes. 495 4.1.4. Symmetrical Size: Session-Sender Packet Format 497 When the Symmetrical Size mode is selected, the Session-Sender SHALL 498 use the following TWAMP-Test Packet Format in Unauthenticated mode: 500 Unauthenticated Mode 501 0 1 2 3 502 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 1 503 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 504 | Sequence Number | 505 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 506 | Timestamp | 507 | | 508 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 509 | Error Estimate | | 510 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 511 | | 512 | | 513 | MBZ (27 octets) | 514 | | 515 | | 516 | | 517 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 518 | | | 519 +-+-+-+-+-+-+-+-+ + 520 . . 521 . Packet Padding . 522 . . 523 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 525 This feature REQUIRES only a new Session-Sender test packet format, 526 the Session-Reflector test packet format is unchanged. 528 4.1.5. Symmetrical Size AND Reflect Octets: Session-Sender Packet 529 Format 531 When both the Symmetrical Size mode and the Reflect Octets mode are 532 selected, the Session-Sender SHALL use the following TWAMP-Test 533 Packet Format in Unauthenticated mode: 535 Unauthenticated Mode 536 0 1 2 3 537 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 1 538 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 539 | Sequence Number | 540 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 541 | Timestamp | 542 | | 543 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 544 | Error Estimate | | 545 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 546 | | 547 | | 548 | MBZ (27 octets) | 549 | | 550 | | 551 | | 552 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 553 | | | 554 +-+-+-+-+-+-+-+-+ + 555 | Packet Padding (to be reflected) | 556 . (length in octets specified in command) . 557 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 558 . . 559 . Additional Packet Padding . 560 . . 561 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 563 In this combined mode, the Packet Padding to be reflected follows the 564 27 MBZ octets. In Authenticated or Encrypted modes, the Packet 565 Padding to be reflected follows the 56 MBZ octets. 567 4.2. Reflector Behavior 569 The TWAMP Reflector follows the procedures and guidelines in section 570 4.2 of [RFC5357], with the following additional functions: 572 o Reflect Octets mode: Designated octets in the "Packet Padding (to 573 be reflected)" field of the Session-Sender's test packet MUST be 574 included in the Session-Reflector's test packet. 576 o Symmetrical Size mode: The Session-Reflector MUST operate using 577 the Session_Reflector Packet Format defined in section 4.1.4, 578 where the Padding Octets are separated from the information 579 fields. 581 4.2.1. Reflect Octets: Session-Reflector Packet Format and Contents 583 The Reflect Padding feature re-designates the packet padding field, 584 as shown below. When the Reflect Octets mode is selected, the 585 Session-Sender SHALL use the following TWAMP-Test Packet Format in 586 Unauthenticated mode: 588 0 1 2 3 589 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 1 590 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 591 | Sequence Number | 592 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 593 | Timestamp | 594 | | 595 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 596 | Error Estimate | MBZ | 597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 598 | Receive Timestamp | 599 | | 600 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 601 | Sender Sequence Number | 602 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 603 | Sender Timestamp | 604 | | 605 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 606 | Sender Error Estimate | MBZ | 607 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 608 | Sender TTL | Packet Padding (from Session-Sender) | 609 +-+-+-+-+-+-+-+-+ + 610 . . 611 + +-+-+-+-+-+-+-+-+ 612 | Packet Padding (from Session-Sender) | | 613 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 614 | | 615 | | 616 . Additional Packet Padding . 617 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 618 The "Packet Padding (from Session-Sender)" field MUST be the same 619 octets as the "Packet Padding (to be reflected)" field in the 620 Session-Sender's test packet, and therefore MUST conform to the 621 length specified in the Request-TW-Session message. 623 When the Server has returned a non-zero value in the "Server octets" 624 field of the Accept Session message (as described in section 3.3), 625 then the Session-Reflector SHALL reflect these octets the same as the 626 rest of the "Packet Padding (to be reflected)" Field. 628 Section 4.2.1 of [RFC5357] recommends a padding truncation process 629 for use in TWAMP. When using that process in conjunction with the 630 Reflect octets mode, the Session-Reflector MUST reflect the 631 designated octets from the Session-Sender's test packet in the 632 "Packet Padding (from Session-Sender)" Field, and MAY re-use 633 additional Packet Padding from the Session-Sender. The Session- 634 Reflector MUST truncate the padding such that the highest number 635 octets are discarded, and the test packet length equals the Session- 636 Sender's packet length. When using the recommended truncation 637 process, the Session-Reflector MUST truncate exactly 27 octets of 638 padding in Unauthenticated mode, and exactly 56 octets in 639 Authenticated and Encrypted modes. 641 In any case, the Session-Reflector MAY re-use the Sender's Packet 642 Padding (since the requirements for padding generation are the same 643 for each). 645 4.2.2. Symmetrical Size: Session-Reflector Packet Format 647 When Symmetrical Size mode is selected, the Session-Reflector packet 648 formats for unauthenticated and authenticated/encrypted modes are 649 identical to the core TWAMP specification, section 4.2.1 of 650 [RFC5357]. Thus, the Session-Reflector test packet format is 651 unchanged. 653 The Session-Reflector MUST construct its test packet using the 654 information in the Session-Sender's test packet. The length of the 655 Session-Reflector's test packet SHALL equal the length of the 656 Session-Sender's test packet. 658 4.2.3. Symmetrical Size AND Reflect Octets: Session-Sender Packet 659 Format 661 When both the Symmetrical Size mode and the Reflect Octets mode are 662 selected, the Session-Reflector MUST operate using the Session- 663 Reflector Packet Format defined in section 4.1.5, where the Padding 664 Octets are separated from the information fields, and the Padding to 665 be Reflected field precedes the Additional Padding. 667 The Session-Reflector SHALL use the same TWAMP-Test Packet Format as 668 specified in section 4.2.1 above. 670 5. Security Considerations 672 These extended modes of operation do not appear to permit any new 673 attacks on hosts communicating with core TWAMP [RFC5357]. 675 The security considerations that apply to any active measurement of 676 live networks are relevant here as well. See [RFC4656] and 677 [RFC5357]. 679 6. IANA Considerations 681 This memo adds two modes to the IANA registry for the TWAMP Modes 682 Field, and describes behavior when the new modes are used. This 683 field is a recognized extension mechanism for TWAMP. 685 6.1. Registry Specification 687 IANA has created a TWAMP-Modes registry (as requested in [RFC5618]). 688 TWAMP-Modes are specified in TWAMP Server Greeting messages and 689 Set-up Response messages, as described in section 3.1 of [RFC5357], 690 consistent with section 3.1 of [RFC4656], and extended by this memo. 691 Modes are indicated by setting bits in the 32-bit Modes field that 692 correspond to values in the Modes registry. For the TWAMP-Modes 693 registry, we expect that new features will be assigned increasing 694 registry values that correspond to single bit positions, unless there 695 is a good reason to do otherwise (more complex encoding than single 696 bit positions may be used in the future, to access the 2^32 value 697 space). 699 6.2. Registry Contents 701 TWAMP Modes Registry is recommended to be augmented as follows: 703 Value Description Semantics Definition 704 -------------------------------------------------------- 705 xxx Reflect Octets this memo, section 3.1 706 Capability new bit position (X) 707 yyy Symmetrical Size this memo, section 3.1 708 Sender Test Packet Format new bit position (Y) 710 >>>IANA: change xxx, yyy, X, Y, and RFC???? to the assigned values 712 The suggested values are 714 X=5, xxx=32 716 Y=6, yyy=64 <<<< 718 7. Acknowledgements 720 The authors thank Steve Baillargeon, Walt Steverson, and Stina Ross 721 for helpful review and comments. 723 8. References 725 8.1. Normative References 727 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 728 Requirement Levels", BCP 14, RFC 2119, March 1997. 730 [RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. 731 Zekauskas, "A One-way Active Measurement Protocol 732 (OWAMP)", RFC 4656, September 2006. 734 [RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. 735 Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)", 736 RFC 5357, October 2008. 738 [RFC5618] Morton, A. and K. Hedayat, "Mixed Security Mode for the 739 Two-Way Active Measurement Protocol (TWAMP)", RFC 5618, 740 August 2009. 742 8.2. Informative References 744 Authors' Addresses 746 Al Morton 747 AT&T Labs 748 200 Laurel Avenue South 749 Middletown,, NJ 07748 750 USA 752 Phone: +1 732 420 1571 753 Fax: +1 732 368 1192 754 Email: acmorton@att.com 755 URI: http://home.comcast.net/~acmacm/ 756 Len Ciavattone 757 AT&T Labs 758 200 Laurel Avenue South 759 Middletown,, NJ 07748 760 USA 762 Phone: +1 732 420 1239 763 Fax: 764 Email: lencia@att.com 765 URI: