idnits 2.17.1 draft-mizrahi-ippm-compact-alternate-marking-04.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == The document doesn't use any RFC 2119 keywords, yet seems to have RFC 2119 boilerplate text. -- The document date (April 14, 2019) is 1838 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 8321 (Obsoleted by RFC 9341) == Outdated reference: A later version (-09) exists of draft-ietf-ippm-multipoint-alt-mark-01 == Outdated reference: A later version (-10) exists of draft-ietf-mpls-rfc6374-sfl-03 == Outdated reference: A later version (-11) exists of draft-ietf-mpls-sfl-framework-04 Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group T. Mizrahi 3 Internet-Draft Huawei Network.IO Innovation Lab 4 Intended status: Informational C. Arad 5 Expires: October 16, 2019 6 G. Fioccola 7 Huawei Technologies 8 M. Cociglio 9 Telecom Italia 10 M. Chen 11 L. Zheng 12 Huawei Technologies 13 G. Mirsky 14 ZTE Corp. 15 April 14, 2019 17 Compact Alternate Marking Methods for Passive and Hybrid Performance 18 Monitoring 19 draft-mizrahi-ippm-compact-alternate-marking-04 21 Abstract 23 This memo introduces new alternate marking methods that require a 24 compact overhead of either a single bit per packet, or zero bits per 25 packet. This memo also presents a summary of alternate marking 26 methods, and discusses the tradeoffs among them. The target audience 27 of this document is network protocol designers; this document is 28 intended to help protocol designers choose the best alternate marking 29 method(s) based on the protocol's constraints and requirements. 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at https://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on October 16, 2019. 48 Copyright Notice 50 Copyright (c) 2019 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (https://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with respect 58 to this document. Code Components extracted from this document must 59 include Simplified BSD License text as described in Section 4.e of 60 the Trust Legal Provisions and are provided without warranty as 61 described in the Simplified BSD License. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 66 1.1. Background . . . . . . . . . . . . . . . . . . . . . . . 3 67 1.2. The Scope of This Document . . . . . . . . . . . . . . . 4 68 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 69 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 5 70 2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 5 71 3. Marking Abstractions . . . . . . . . . . . . . . . . . . . . 5 72 4. Double Marking . . . . . . . . . . . . . . . . . . . . . . . 7 73 5. Single-bit Marking . . . . . . . . . . . . . . . . . . . . . 8 74 5.1. Single Marking Using the First Packet . . . . . . . . . . 8 75 5.2. Single Marking using the Mean Delay . . . . . . . . . . . 8 76 5.3. Single Marking using a Multiplexed Marking Bit . . . . . 8 77 5.3.1. Overview . . . . . . . . . . . . . . . . . . . . . . 8 78 5.3.2. Timing and Synchronization Aspects . . . . . . . . . 9 79 5.4. Pulse Marking . . . . . . . . . . . . . . . . . . . . . . 11 80 6. Zero Marking Hashed . . . . . . . . . . . . . . . . . . . . . 12 81 6.1. Hash-based Sampling . . . . . . . . . . . . . . . . . . . 12 82 6.1.1. Hashed Pulse Marking . . . . . . . . . . . . . . . . 13 83 6.1.2. Hashed Step Marking . . . . . . . . . . . . . . . . . 13 84 7. Single Marking Hashed . . . . . . . . . . . . . . . . . . . . 13 85 8. Summary of Marking Methods . . . . . . . . . . . . . . . . . 14 86 9. Alternate Marking using Reserved Values . . . . . . . . . . . 19 87 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 88 11. Security Considerations . . . . . . . . . . . . . . . . . . . 20 89 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 90 12.1. Normative References . . . . . . . . . . . . . . . . . . 20 91 12.2. Informative References . . . . . . . . . . . . . . . . . 20 92 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 94 1. Introduction 96 1.1. Background 98 Alternate marking, defined in [RFC8321], is a method for measuring 99 packet loss, packet delay, and packet delay variation. Typical delay 100 measurement protocols require the two measurement points (MPs) to 101 exchange timestamped test packets. In contrast, the alternate 102 marking method does not require control packets to be exchanged. 103 Instead, every data packet carries a color indicator, which divides 104 the traffic into consecutive blocks of packets. 106 The color value is toggled periodically, as illustrated in Figure 1. 108 A: packet with color 0 109 B: packet with color 1 111 Packets AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA 112 Time ----------------------------------------------------------> 113 | | | | | 114 | Block 1 | Block 2 | Block 3 | Block 4 | Block 5 ... 115 | | | | | 116 Color 0000000000 1111111111 0000000000 1111111111 0000000000 118 Figure 1: Alternate marking: packets are monitored on a per-color 119 basis. 121 Alternate marking is used between two MPs, the initiating MP, and the 122 monitoring MP. The initiating MP incorporates the marking field into 123 en-route packets, allowing the monitoring MP to use the marking field 124 in order to bind each packet to the corresponding block. 126 Each of the MPs maintains two counters, one per color. At the end of 127 each block the counter values can be collected by a central 128 management system, and analyzed; the packet loss can be computed by 129 comparing the counter values of the two MPs. 131 When using alternate marking delay measurement can be performed in 132 one of three ways (as per [RFC8321]): 134 o Single marking using the first packet: in this method each packet 135 uses a single marking bit, used as a color indicator. The first 136 packet of each block is used by both MPs as a reference for delay 137 measurement. The timestamp of this packet is measured by the two 138 measurement points, and can be collected by the mangement system 139 from each of the measurement points, which can compute the path 140 delay by comparing the two timestamps. The drawback of this 141 approach is that it is not accurate when packets arrive out-of- 142 order, as the two MPs may have a different view of which packet 143 was the first in the block. 145 o Single marking using the mean delay: as in the previous method, 146 each packet uses a single marking method, indicating the color. 147 Each of the MPs computes the average packet timestamp of each 148 block. The management system can then compute the delay by 149 comparing the average times of the two MPs. The drawback of this 150 approach is that it may be computationally heavy, or difficult to 151 implement at the data plane. 153 o Double marking: each packet uses two marking bits. One bit is 154 used as a color indicator, and one is used as a timestamping 155 indicator. This method resolves the drawbacks raised for the two 156 previous methods, at the expense of an extra bit in the packet 157 header. 159 The double marking method is the most straightforward approach. It 160 allows for accurate measurement without incurring expensive 161 computational load. However, in some cases allocating two bits for 162 passive measurement is not possible. For example, if alternate 163 marking is implemented over IPv4, allocating 2 marking bits in the 164 IPv4 header is challenging, as every bit in the 20-octet header is 165 costly; one of the possible approaches discussed in [RFC8321] is to 166 reserve one or two bits from the DSCP field for remarking. In this 167 case every marking bit comes at the expense of reducing the DSCP 168 range by a factor of two. 170 1.2. The Scope of This Document 172 This memo extends the marking methods of [RFC8321], and introduces 173 methods that require a single marking bit, or zero marking bits. 175 Two single-bit marking methods are proposed, multiplexed marking and 176 pulse marking. In multiplexed marking the color indicator and the 177 timestamp indicator are multiplexed into a single bit, providing the 178 advantages of the double marking method while using a single bit in 179 the packet header. In pulse marking both delay and loss measurement 180 are triggered by a 'pulse' value in a single marking field. 182 This document also discusses zero-bit marking methods that leverage 183 well-known hash-based selection approaches ([RFC5474], [RFC5475]). 185 Alternate marking is discussed in this memo as a single-bit or a two- 186 bit marking method. However, these methods can similarly be applied 187 to larger fields, such as an IPv6 Flow Label or an MPLS Label; 188 single-bit marking can be applied using two reserved values, and two- 189 bit marking can be applied using four reserved values. Marking based 190 on reserved values is further discussed in this document, including 191 its application to MPLS and IPv6. 193 Finally, this memo summarizes the alternate marking methods, and 194 discusses the tradeoffs among them. It is expected that different 195 network protocols will have different constraints, and therefore may 196 choose to use different alternate marking methods. In some cases it 197 may be preferable to support more than one marking method; in this 198 case the particular marking method may be signaled through the 199 control plane. 201 2. Terminology 203 2.1. Requirements Language 205 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 206 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 207 document are to be interpreted as described in RFC 2119 [RFC2119]. 209 2.2. Abbreviations 211 The following abbreviations are used in this document: 213 DSCP Differentiated Services Code Point 215 DM Delay Measurement 217 LM Loss Measurement 219 LSP Label Switched Path 221 MP Measurement Point 223 MPLS Multiprotocol Label Switching 225 SFL Synonymous Flow Label [I-D.ietf-mpls-sfl-framework] 227 3. Marking Abstractions 229 The marking methods that were discussed in Section 1, as well as the 230 methods introduced in this document, use two basic abstractions, 231 pulse detection, and step detection. 233 The common thread along the various marking methods is that one or 234 two marking bits are used by the MPs to signal a measurement event. 235 The value of the marking bit indicates when the event takes place, in 236 one of two ways: 238 Pulse An event is detected when the value of the marking bit 239 is toggled in a single packet. 241 Step An event is detected when the value of the marking bit 242 is toggled, and remains at the new value. 244 The double marking method (Section 1) uses pulse-based detection for 245 DM, and step-based detection for LM. 247 Pulse-based detection affects the processing of a single packet; the 248 packet that indicates the pulse is processed differently than the 249 packets around it. For example, in the double marking method, the 250 marked packet is timestamped for DM, without affecting the packets 251 before or after it. Note that if the marked packet is lost, no pulse 252 is detected, yielding a missing measurement (see Figure 2). 254 P: indicates a packet 256 Packets PPPPPPPPPP PPPPPPPPPP PPPPPPPPPP PPPPPPPPPP PPPPPPPPPP 257 Time ----------------------------------------------------------> 258 Marking bit 0000010000 0000010000 0000010000 0000010000 00000 0000 259 ^ ^ ^ ^ ^ 260 Pulse-based | | | | | 261 detection | | | | | 262 Dropped packet: 263 no detection 265 Figure 2: Pulse-based Detection. 267 In step-based detection the event is detected by observing a value 268 change in stream of packets. Specifically, when the step approach is 269 used for LM (as in the double marking method), two counters are used 270 per flow; each MP decides which counter to use based on the value of 271 the marking bit. Thus, the step-based approach allows accurate 272 counting even when packets arrive out-of-order (see Figure 3). When 273 the step approach is used for DM (e.g., single marking using the 274 first packet), out-of-order causes the delay measurement to be false, 275 without any indication to the management system. 277 P: indicates a packet 279 Packets PPPPPPPPPP PPPPPPPPPP PPPPPPPPPP PPPPPPPPPP PPPPPPPPPP 280 Time ----------------------------------------------------------> 281 Marking bit 0000000000 1111111111 000000000 10111111111 0000000000 282 ^ ^ ^ ^ 283 Step-based | | | | 284 detection | | | | 285 out-of-order 287 Figure 3: Step-based Detection. 289 4. Double Marking 291 The two-bit marking method of [RFC8321] uses two marking bits: a 292 color indicator, and a delay measurement indicator. The color bit is 293 used for step-based LM, while the delay bit is used as a pulse-based 294 DM trigger. This double marking approach is the most straightforward 295 of the approaches discussed in this memo, as it allows accurate 296 measurement, it is resilient to out-of-order delivery, and is 297 relatively simple to implement. The main drawback is that it 298 requires two bits, which are not always available. 300 Figure 4 illustrates the double marking method: each block of packets 301 includes a packet that is marked for timestamping, and therefore has 302 its delay bit set. 304 A: packet with color 0 305 B: packet with color 1 307 Packets AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA 308 Time ----------------------------------------------------------> 309 | | | | | 310 | Block 1 | Block 2 | Block 3 | Block 4 | Block 5 ... 311 | | | | | 312 Color bit 0000000000 1111111111 0000000000 1111111111 0000000000 313 Delay bit 0000100000 0000100000 0000100000 0000100000 0001000000 314 ^ ^ ^ ^ ^ 315 Packets | | | | | 316 marked for | | | | | 317 timestamping | | | | | 319 Figure 4: The double marking method. 321 5. Single-bit Marking 323 5.1. Single Marking Using the First Packet 325 This method uses a single marking bit that indicates the color, as 326 described in [RFC8321]. Both LM and DM are implemented using a step- 327 based approach; LM is implemented using two color-based counters per 328 flow. The first packet of every period is used by the two MPs as the 329 reference for measuring the delay. As denoted above, the delay 330 computed in this method may be erroneous when packets are delivered 331 out-of-order. 333 A: packet with color 0 334 B: packet with color 1 336 Packets AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA 337 Time ----------------------------------------------------------> 338 | | | | | 339 | Block 1 | Block 2 | Block 3 | Block 4 | Block 5 ... 340 | | | | | 341 Color bit 0000000000 1111111111 0000000000 1111111111 0000000000 342 ^ ^ ^ ^ ^ 343 Packets | | | | | 344 used for DM | | | | | 346 Figure 5: Single marking using the first packet of the block. 348 5.2. Single Marking using the Mean Delay 350 As in the first-packet approach, in the mean delay approach 351 ([RFC8321]) a single marking bit is used to indicate the color, 352 enabling step-based loss measurement. Delay is measured in each 353 period by averaging the measured delay over all the packets in the 354 period. As discussed above, this approach is not sensitive to out- 355 of-order delivery, but may be heavy from a computational perspective. 357 5.3. Single Marking using a Multiplexed Marking Bit 359 5.3.1. Overview 361 This section introduces a method that uses a single marking bit that 362 serves two purposes: a color indicator, and a timestamp indicator. 363 The double marking method that was discussed in the previous section 364 uses two 1-bit values: a color indicator C, and a timestamp indicator 365 T. The multiplexed marking bit, denoted by M, is an exclusive or 366 between these two values: M = C XOR T. 368 An example of the use of the multiplexed marking bit is depicted in 369 Figure 6. The example considers two routers, R1 and R2, that use the 370 multiplexed bit method to measure traffic from R1 to R2. In each 371 block R1 designates one of the packets for delay measurement. In 372 each of these designated packets the value of the multiplexed bit is 373 reversed compared to the other packets in the same block, allowing R2 374 to distinguish the designated packets from the other packets. 376 A: packet with color 0 377 B: packet with color 1 379 Packets AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA 380 Time ----------------------------------------------------------> 381 | | | | | 382 | Block 1 | Block 2 | Block 3 | Block 4 | Block 5 ... 383 | | | | | 384 Color 0000000000 1111111111 0000000000 1111111111 0000000000 385 ^ ^ ^ ^ ^ 386 Packets | | | | | 387 marked for | | | | | 388 timestamping | | | | | 389 v v v v v 390 Muxed bit 0000100000 1111011111 0000100000 1111101111 0001000000 392 Figure 6: Alternate marking with multiplexed bit. 394 5.3.2. Timing and Synchronization Aspects 396 It is assumed that all MPs are synchronized to a common reference 397 time with an accuracy of +/- A/2. Thus, the difference between the 398 clock values of any two MPs is bounded by A. Clocks can be 399 synchronized for example using NTP [RFC5905], PTP [IEEE1588], or by 400 other means. The common reference time is used for dividing the time 401 domain into equal-sized measurement periods, such that all packets 402 forwarded during a measurement period have the same color, and 403 consecutive periods have alternating colors. 405 The single marking bit incorporates two multiplexed values. From the 406 monitoring MP's perspective, the two values are Time-Division 407 Multiplexed (TDM), as depicted in Figure 7. It is assumed that the 408 start time of every measurement period is known to both the 409 initiating MP and the monitoring MP. If the measurement period is L, 410 then during the first and the last L/4 time units of each block the 411 marking bit is interpreted by the monitoring MP as a color indicator. 412 During the middle part of the block, the marking bit is interpreted 413 as a timestamp indicator; if the value of this bit is different than 414 the color value, the corresponding packet is used as a reference for 415 delay measurement. 417 +--- Beginning of measurement period 418 | 419 v 421 ...BBBBBBBBB | AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | BBBBBBBBB... 422 |<======================================>| 423 | L | 424 <========>|<========><==================><========>|<========> 425 L/4 L/4 L/2 L/4 L/4 427 <===================><==================><===================> 428 Detect color Detect timestamping Detect color 429 change indication change 431 Figure 7: Multiplexed marking field interpretation at the receiving 432 measurement point. 434 In order to prevent ambiguity in the receiver's interpretation of the 435 marking field, the initiating MP is permitted to set the timestamp 436 indication only during a specific interval, as depicted in Figure 8. 437 Since the receiver is willing to receive the timestamp indication 438 during the middle L/2 time units of the block, the sender refrains 439 from sending the timestamp indication during a guardband interval of 440 d time units at the beginning and end of the L/2-period. 442 +--- Beginning of measurement period 443 | 444 v 446 ...BBBBBBBBB | AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | BBBBBBBBB... 447 |<======================================>| 448 | L | 449 <========>|<========>|<================>|<========>| 450 L/4 L/4 | L/2 | L/4 451 <=>|<=> <=>|<=> 452 d d d d 453 <==========> 454 permissible 455 timestamping 456 indication 457 interval 459 Figure 8: A time domain view. 461 The guardband d is given by d = A + D_max - D_min, where A is the 462 clock accuracy, D_max is an upper bound on the network delay between 463 the MPs, and D_min is a lower bound on the delay. It is 464 straightforward from Figure 8 that d < L/4 must be satisfied. The 465 latter implies a minimal requirement on the synchronization accuracy. 467 All MPs must be synchronized to the same reference time with an 468 accuracy of +/- L/8. Depending on the system topology, in some 469 systems the accuracy requirement will be even more stringent, subject 470 to d < L/4. Note that the accuracy requirement of the conventional 471 alternate marking method [RFC8321] is +/- L/2, while the multiplexed 472 marking method requires an accuracy of +/- L/8. 474 Note that we assume that the middle L/2-period is designated as the 475 timestamp indication period, allowing a sufficiently long guardband 476 between the transitions. However, a system may be configured to use 477 a longer timestamp indication period or a shorter one, if it is 478 guaranteed that the synchronization accuracy meets the guardband 479 requirements (i.e., the constraints on d). 481 5.4. Pulse Marking 483 Pulse marking uses a single marking bit that is used as a trigger for 484 both LM and DM. In this method the two MPs maintain a single per- 485 flow counter for LM, in contrast to the color-based methods which 486 require two counters per flow. In each block one of the packets is 487 marked. The marked packet triggers two actions in each of MPs: 489 o The timestamp is captured for DM. 491 o The value of the counter is captured for LM. 493 In each period, each of the MPs exports the timestamp and counter- 494 stamp to the management system, which can then compute the loss and 495 delay in that period. It should be noted that as in [RFC8321], if 496 the length of the measurement period is L time units, then all 497 network devices must be synchronized to the same clock reference with 498 an accuracy of +/- L/2 time units. 500 The pulse marking approach is illustrated in Figure 9. Since both LM 501 and DM use a pulse-based trigger, if the marked packet is lost then 502 no measurement is available in this period. Moreover, the LM 503 accuracy may be affected by out-of-order delivery. 505 P: packet - all packets have the same color 507 Packets PPPPPPPPPP PPPPPPPPP PPPPPPPPPP PPPPPPPPPP PPPPPPPPPP 508 Time ----------------------------------------------------------> 509 | | | | | 510 | Block 1 | Block 2 | Block 3 | Block 4 | Block 5 ... 511 | | | | | 512 ^ ^ ^ ^ ^ 513 Packets | | | | | 514 marked for | | | | | 515 DM and LM | | | | | 516 v v v v v 517 Marking bit 0000100000 0000100000 0000100000 0000010000 0001000000 519 Figure 9: Pulse marking method. 521 6. Zero Marking Hashed 523 6.1. Hash-based Sampling 525 Hash based selection [RFC5475] is a well-known method for sampling a 526 subset of packets. As defined in [RFC5475]: 528 A Hash Function h maps the Packet Content c, or some portion of 529 it, onto a Hash Range R. The packet is selected if h(c) is an 530 element of S, which is a subset of R called the Hash Selection 531 Range. 533 Hash-based selection can be leveraged as a marking method, allowing a 534 zero-bit marking approach. Specifically, the pulse and step 535 abstractions can be implemented using hashed selection: 537 o Hashed pulse-based trigger: in this approach, a packet is selected 538 if h(c) is an element of S, which is a strict subset of the hash 539 range R. When |S|<<|R|, the average sampling period is long, 540 reducing the probability of ambiguity between consecutive 541 packets. |S| and |R| denote the number of elements in S and R, 542 respectively. 544 o Hashed step-based trigger: the hash values of a given traffic flow 545 are said to be monotonically increasing if for two packets p1 and 546 p2, if p1 is sent before p2 then h(p1)<=h(p2). If it is 547 guaranteed that the hash values of a flow are monotonically 548 increasing, then a step-based approach can be used on the range R. 549 For example, in an IPv4 flow the Identification field can be used 550 as the hash value of each packet. Since the Identification field 551 is monotonically increasing, the step-based trigger can be 552 implemented using consecutive ranges of the Identification value. 553 For example, the fourth bit of the Identification field is toggled 554 every 8 packets. Thus, a possible hash function simply takes the 555 fourth bit of the Identification field as the hash value. This 556 hash value is toggled every 8 packets, simulating the alternate 557 marking behavior of Section 4. 559 Note that as opposed to the double marking and single marking 560 methods, hashed sampling is not based on fixed time intervals, as the 561 duration between sampled packets depends only on the hash value. 563 It is also important to note that all methods that use hash-based 564 marking require the hash function and the set S to be configured 565 consistently across the MPs. 567 6.1.1. Hashed Pulse Marking 569 In this approach a hash is computed over the packet content, and both 570 LM and DM are triggered based on the pulse-based trigger 571 (Section 6.1). A pulse is detected when the hash value h(c) is equal 572 to one of the values in S. The hash function h and the set S 573 determine the probability (or frequency) of the pulse event. 575 6.1.2. Hashed Step Marking 577 As in the previous approach, hashed step marking also uses a hash 578 that is computed over the packet content. In this approach DM is 579 performed using a pulse-based trigger, whereas the LM trigger is 580 step-based (Section 6.1). The main drawback of this method is that 581 the step-based trigger is possible only under the assumption that the 582 hash function is monotonically increasing, which is not necessarily 583 possible in all cases. Specifically, a measured flow is not 584 necessarily an IPv4 5-tuple. For example, a measured flow may 585 include multiple IPv4 5-tuple flows, and in this case the 586 Identification field is not monotonically increasing. 588 7. Single Marking Hashed 590 Mixed hashed marking combines the single marking approach with hash- 591 based sampling. A single marking bit is used in the packet header as 592 a color indicator, while a hash-based pulse is used to trigger DM. 593 Although this method requires a single bit, it is described in this 594 section as it is closely related to the other hash-based methods that 595 require zero marking bits. 597 The hash-based selection for DM can be applied in one of two possible 598 approaches: the basic approach, and the dynamic approach. In the 599 basic approach, packets forwarded between two MPs, MP1 and MP2, are 600 selected using a hash function, as described above. One of the 601 challenges is that the frequency of the sampled packets may vary 602 considerably, making it difficult for the management system to 603 correlate samples from the two MPs. Thus, the dynamic approach can 604 be used. 606 In the dynamic hash-based sampling, alternate marking is used to 607 create divide time into periods, so that hash-based samples are 608 divided into batches, allowing to anchor the selected samples to 609 their period. Moreover, by dynamically adapting the length of the 610 hash value, the number of samples is bounded in each marking period. 611 This can be realized by choosing first the maximum number of samples 612 (NMAX) to be used with the initial hash length. The algorithm starts 613 with only few hash bits, that permit to select a greater percentage 614 of packets (e.g. with 1 bit of hash half of the packets are sampled). 615 When the number of selected packets reaches NMAX, a hashing bit is 616 added. As a consequence, the sampling proceeds at half of the 617 original rate and the packets already selected that do not match the 618 new hash are discarded. This step can be repeated iteratively. It 619 is assumed that each sample includes the timestamp (used for DM) and 620 the hash value, allowing the management system to match the samples 621 received from the two MPs. 623 The dynamic process statistically converges at the end of a marking 624 period and the number of selected samples beyond the initial NMAX 625 samples mentioned above is between NMAX/2 and NMAX. Therefore, the 626 dynamic approach paces the sampling rate, allowing to bound the 627 number of sampled packets per sampling period. 629 8. Summary of Marking Methods 631 This section summarizes the marking methods described in this memo. 632 Each row in the table of Figure 10 represents a marking method. For 633 each method the table specifies the number of bits required in the 634 header, the number of counters per flow for LM, the methods used for 635 LM and DM (pulse or step), and also the resilience to disturbances. 637 +--------------+----+----+------+------+-------------+-------------+ 638 | Method |# of|# of|LM |DM |Resilience to|Resilience to| 639 | |bits|coun|Method|Method|Reordering |Packet drops | 640 | | |ters| | +------+------+------+------+ 641 | | | | | | LM | DM | LM | DM | 642 +--------------+----+----+------+------+------+------+------+------+ 643 |Single marking| 1 | 2 |Step |Step | + | -- | + | -- | 644 |- 1st packet | | | | | | | | | 645 +--------------+----+----+------+------+------+------+------+------+ 646 |Single marking| 1 | 2 |Step |Mean | + | + | + | - | 647 |- mean delay | | | | | | | | | 648 +--------------+----+----+------+------+------+------+------+------+ 649 |Double marking| 2 | 2 |Step |Pulse | + | + | + | = | 650 +--------------+----+----+------+------+------+------+------+------+ 651 |Single marking| 1 | 2 |Step |Pulse | + | + | + | = | 652 |multiplexed | | | | | | | | | 653 +--------------+----+----+------+------+------+------+------+------+ 654 |Pulse marking | 1 | 1 |Pulse |Pulse | -- | + | - | = | 655 +--------------+----+----+------+------+------+------+------+------+ 656 |Zero marking | 0 | 1 |Hashed|Hashed| -- | + | - | + | 657 |hashed | |(2) |pulse |pulse | (-) | | | | 658 | | | |(step)| | | | | | 659 +--------------+----+----+------+------+------+------+------+------+ 660 |Single marking| 1 | 2 |Step |Hashed| + | + | + | + | 661 |hashed | | | |pulse | | | | | 662 +--------------+----+----+------+------+------+------+------+------+ 664 + Accurate measurement. 665 = Invalidate only if a measured packet is lost (detectable) 666 - No measurement in case of disturbance (detectable). 667 -- False measurement in case of disturbance (not detectable). 669 Figure 10: Detailed Summary of Marking Methods 671 In the context of this comparison two possible disturbances are 672 considered: out-of-order delivery, and packet drops. Generally 673 speaking, pulse based methods are sensitive to packet drops, since if 674 the marked packet is dropped no measurement is recorded in the 675 current period. Notably, a missing measurement is detectable by the 676 management system, and is not as severe as a false measurement. 677 Step-based triggers are generally resilient to out-of-order delivery 678 for LM, but are not resilient to out-of-order delivery for DM. 679 Notably, a step-based trigger may yield a false delay measurement 680 when packets are delivered out-of-order, and this inaccuracy is not 681 detectable. 683 As mentioned above, the double marking method is the most 684 straightforward approach, and is resilient to most of the 685 disturbances that were analyzed. Its obvious drawback is that it 686 requires two marking bits. 688 Several single marking methods are discussed in this memo. In this 689 case there is no clear verdict which method is the optimal one. The 690 first packet method may be simple to implement, but may present 691 erroneous delay measurements in case of dropped or reordered packets. 692 Arguably, the mean delay approach and the multiplexed approach may be 693 more difficult to implement (depending on the underlying platform), 694 but are more resilient to the disturbances that were considered here. 695 Note that the computational complexity of the mean delay approach can 696 be reduced by combining it with a hashed approach, i.e., by computing 697 the mean delay over a hash-based subset of the packets. The pulse 698 marking method requires only a single counter per flow, while the 699 other methods require two counters per flow. 701 The hash-based sampling approaches reduce the overhead to zero bits, 702 which is a significant advantage. However, the sampling period in 703 these approaches is not associated with a fixed time interval. 704 Therefore, in some cases adjacent packets may be selected for the 705 sampling, potentially causing measurement errors. Furthermore, when 706 the traffic rate is low, measurements may become signifcantly 707 infrequent. 709 It should be noted that most of the marking methods that were 710 presented in this memo are intended for point-to-point measurements, 711 e.g., from MP1 to MP2 in Figure 11. In point-to-multipoint 712 measurements, the mean delay method can be used to measure the loss 713 and delay of the entire point-to-multipoint flow (which includes all 714 the traffic from MP3 to either MP4 or MP5), while other methods such 715 as double marking can be used to measure the point-to-point 716 performance, for example from MP3 to MP5. Alternate marking in 717 multipoint scenarios is discussed in detail in 718 [I-D.ietf-ippm-multipoint-alt-mark]. 720 MP1 MP2 MP3 MP4 721 +--+ +--+ +--+ +--+ +--+ 722 | |---------->| | | |----->| |----->| | 723 +--+ +--+ +--+ +--+ +--+ 724 | 725 | MP5 726 | +--+ 727 +------>| | 728 +--+ 730 Point-to-point measurement Point-to-multipoint measurement 732 Figure 11: Point-to-point and point-to-multipoint measurements. 734 It is clear from the previous table that packet loss measurement can 735 be considered resilient to both reordering and packet drops if at 736 least one bit is used with a step-based approach. Thus, since the 737 packet loss can be considered obvious, the previous table can be 738 simplified into Figure 12, where only the characteristics of delay 739 measurements are highlighted, along with multipoint-to-multipoint 740 delay measurement compatibility (refer to 741 [I-D.ietf-ippm-multipoint-alt-mark] for more details). 743 +--------------+----+--------+------------+------------+-----------+ 744 | Marking |# of|LM |DM |DM |DM | 745 | Method |bits|on |Resilience |Resilience |Multipoint | 746 | | |All |to |to |compatible | 747 | | |Packets |Reordering |Packet drops| | 748 +--------------+----+--------+------------+------------+-----------+ 749 |Single marking| 1 | Yes | -- | - | No | 750 |- 1st packet | | | | | | 751 +--------------+----+--------+------------+------------+-----------+ 752 |Single marking| 1 | Yes | + | - | Yes | 753 |- mean delay | | | | | | 754 +--------------+----+--------+------------+------------+-----------+ 755 |Double marking| 2 | Yes | + | = | No | 756 +--------------+----+--------+------------+------------+-----------+ 757 |Single marking| 1 | Yes | + | = | No | 758 |multiplexed | | | | | | 759 +--------------+----+--------+------------+------------+-----------+ 760 |Pulse marking | 1 | No | + | = | No | 761 +--------------+----+--------+------------+------------+-----------+ 762 |Zero marking | 0 | No | + | + | Yes | 763 |hashed | | | | | | 764 | | | | | | | 765 +--------------+----+--------+------------+------------+-----------+ 766 |Single marking| 1 | Yes | + | + | Yes | 767 |hashed | | | | | | 768 +--------------+----+--------+------------+------------+-----------+ 770 + Accurate measurement. 771 = Invalidate only if a measured packet is lost (detectable) 772 - No measurement in case of disturbance (detectable). 773 -- False measurement in case of disturbance (not detectable). 775 Figure 12: Summary of Marking Methods: focus on Delay Measurement 777 In the context of delay measurement, both zero marking hashed and 778 single marking hashed are resilient to packet drops. Using double 779 marking it could also be possible to perform an accurate measurement 780 in case of packet drops, as long as the packet that is marked for DM 781 is not dropped. 783 The single marking hashed method seems the most complete approach, 784 especially because it is also compatible with multipoint-to- 785 multipoint measurements. 787 9. Alternate Marking using Reserved Values 789 As mentioned in Section 1, a marking bit is not necessarily a single 790 bit, but may be implemented by using two well-known values in one of 791 the header fields. Similarly, two-bit marking can be implemented 792 using four reserved values. 794 A notable example is MPLS Synonymous Flow Labels (SFL), as defined in 795 [I-D.ietf-mpls-rfc6374-sfl]. Two MPLS Label values can be used to 796 indicate the two colors of a given LSP: the original Label value, and 797 an SFL value. A similar approach can be applied to IPv6 using the 798 Flow Label field. 800 The following example illustrates how alternate marking can be 801 implemented using reserved values. The bit multiplexing approach of 802 Section 5.3 is applicable not only to single-bit color indicators, 803 but also to two-value indicators; instead of using a single bit that 804 is toggled between '0' and '1', two values of the indicator field, U 805 and W, can be used in the same manner, allowing both loss and delay 806 measurement to be performed using only two reserved values. Thus, 807 the multiplexing approach of Figure 6 can be illustrated more 808 generally with two values, U and W, as depicted in Figure 13. 810 A: packet with color 0 811 B: packet with color 1 813 Packets AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA 814 Time ----------------------------------------------------------> 815 | | | | | 816 | Block 1 | Block 2 | Block 3 | Block 4 | Block 5 ... 817 | | | | | 818 Color 0000000000 1111111111 0000000000 1111111111 0000000000 819 ^ ^ ^ ^ ^ 820 Packets | | | | | 821 marked for | | | | | 822 timestamping | | | | | 823 v v v v v 824 Muxed UUUUWUUUUU WWWWUWWWWW UUUUWUUUUU WWWWWUWWWW UUUWUUUUUU 825 marking 826 values 828 Figure 13: Alternate marking with two multiplexed marking values, U 829 and W. 831 10. IANA Considerations 833 This memo includes no requests from IANA. 835 11. Security Considerations 837 The security considerations of the alternate marking method are 838 discussed in [RFC8321]. The analysis of Section 8 emphasizes the 839 sensitivity of some of the alternate marking methods to packet drops 840 and to packet reordering. Thus, a malicious attacker may attempt to 841 tamper with the measurements by either selectively dropping packets, 842 or by selectively reordering specific packets. The multiplexed 843 marking method Section 5.3 that is defined in this document requires 844 slightly more stringent synchronization than the conventional marking 845 method, potentially making the method more vulnerable to attacks on 846 the time synchronization protocol. A detailed discussion about the 847 threats against time protocols and how to mitigate them is presented 848 in [RFC7384]. 850 12. References 852 12.1. Normative References 854 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 855 Requirement Levels", BCP 14, RFC 2119, 856 DOI 10.17487/RFC2119, March 1997, 857 . 859 [RFC8321] Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli, 860 L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi, 861 "Alternate-Marking Method for Passive and Hybrid 862 Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321, 863 January 2018, . 865 12.2. Informative References 867 [I-D.ietf-ippm-multipoint-alt-mark] 868 Fioccola, G., Cociglio, M., Sapio, A., and R. Sisto, 869 "Multipoint Alternate Marking method for passive and 870 hybrid performance monitoring", draft-ietf-ippm- 871 multipoint-alt-mark-01 (work in progress), March 2019. 873 [I-D.ietf-mpls-rfc6374-sfl] 874 Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S., 875 Mirsky, G., and G. Fioccola, "RFC6374 Synonymous Flow 876 Labels", draft-ietf-mpls-rfc6374-sfl-03 (work in 877 progress), December 2018. 879 [I-D.ietf-mpls-sfl-framework] 880 Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S., 881 and G. Mirsky, "Synonymous Flow Label Framework", draft- 882 ietf-mpls-sfl-framework-04 (work in progress), December 883 2018. 885 [IEEE1588] 886 IEEE, "IEEE 1588 Standard for a Precision Clock 887 Synchronization Protocol for Networked Measurement and 888 Control Systems Version 2", 2008. 890 [RFC5474] Duffield, N., Ed., Chiou, D., Claise, B., Greenberg, A., 891 Grossglauser, M., and J. Rexford, "A Framework for Packet 892 Selection and Reporting", RFC 5474, DOI 10.17487/RFC5474, 893 March 2009, . 895 [RFC5475] Zseby, T., Molina, M., Duffield, N., Niccolini, S., and F. 896 Raspall, "Sampling and Filtering Techniques for IP Packet 897 Selection", RFC 5475, DOI 10.17487/RFC5475, March 2009, 898 . 900 [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, 901 "Network Time Protocol Version 4: Protocol and Algorithms 902 Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, 903 . 905 [RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in 906 Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384, 907 October 2014, . 909 Authors' Addresses 911 Tal Mizrahi 912 Huawei Network.IO Innovation Lab 913 Israel 915 Email: tal.mizrahi.phd@gmail.com 917 Carmi Arad 919 Email: carmi.arad@gmail.com 921 Giuseppe Fioccola 922 Huawei Technologies 924 Email: giuseppe.fioccola@huawei.com 925 Mauro Cociglio 926 Telecom Italia 927 Via Reiss Romoli, 274 928 Torino 10148 929 Italy 931 Email: mauro.cociglio@telecomitalia.it 933 Mach(Guoyi) Chen 934 Huawei Technologies 936 Email: mach.chen@huawei.com 938 Lianshu Zheng 939 Huawei Technologies 941 Email: vero.zheng@huawei.com 943 Greg Mirsky 944 ZTE Corp. 946 Email: gregimirsky@gmail.com