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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 TRILL Working Group Donald Eastlake 2 INTERNET-DRAFT Huawei 3 Intended status: Proposed Standard Bob Briscoe 4 Simula Research Lab 5 Expires: November 27, 2017 May 28, 2017 7 TRILL: ECN (Explicit Congestion Notification) Support 8 10 Abstract 12 Explicit congestion notification (ECN) allows a forwarding element to 13 notify downstream devices, including the destination, of the onset of 14 congestion without having to drop packets. This can improve network 15 efficiency through better flow control without packet drops. This 16 document extends ECN to TRILL switches, including integration with IP 17 ECN, and provides for ECN marking in the TRILL Header Extension Flags 18 Word (see RFC 7179). 20 Status of This Memo 22 This Internet-Draft is submitted to IETF in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Distribution of this document is unlimited. Comments should be sent 26 to the TRILL working group mailing list . 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF), its areas, and its working groups. Note that 30 other groups may also distribute working documents as Internet- 31 Drafts. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 The list of current Internet-Drafts can be accessed at 39 http://www.ietf.org/1id-abstracts.html. The list of Internet-Draft 40 Shadow Directories can be accessed at 41 http://www.ietf.org/shadow.html. 43 Table of Contents 45 1. Introduction............................................3 46 1.1 Conventions used in this document......................4 48 2. The ECN Specific Extended Header Flags..................6 50 3. ECN Support.............................................7 51 3.1 Ingress ECN Support....................................7 52 3.2 Transit ECN Support....................................7 53 3.3 Egress ECN Support.....................................8 55 4. TRILL Support for ECN Variants.........................10 56 4.1 Pre-Congestion Notification (PCN).....................10 57 4.2 Low Latency, Low Loss, Scalable Throughput (L4S)......11 59 5. IANA Considerations....................................12 60 6. Security Considerations................................13 61 7. Acknowledgements.......................................13 63 Normative References......................................14 64 Informative References....................................15 66 Appendix A. TRILL Transit RBridge Behavior to Support L4S.16 68 Authors' Addresses........................................18 70 1. Introduction 72 Explicit congestion notification (ECN [RFC3168]) allows a forwarding 73 element, such as a router, to notify downstream devices, including 74 the destination, of the onset of congestion without having to drop 75 packets. This can improve network efficiency through better flow 76 control without packet drops. The forwarding element can explicitly 77 mark a proportion of packets in an ECN field instead of dropping the 78 packet. For example, a two-bit field is available for ECN marking in 79 IP headers. 81 ............................. 82 . . 83 +---------+ . 84 +------+ | Ingress | . 85 |Source| +->| RBridge | . +----------+ 86 +---+--+ | | RB1 | . |Forwarding| 87 | | +------+--+ +----------+ . | Element | 88 v | . | | Transit | . | Y | 89 +-------+--+ . +---->| RBridges | . +--------+-+ 90 |Forwarding| . | RBn | . ^ | 91 | Element | . +-------+--+ +---------+ | v 92 | X | . | | Egress | | +-----------+ 93 +----------+ . +---->| RBridge +-+ |Destination| 94 . | RB9 | +-----------+ 95 . TRILL +---------+ 96 . campus . 97 ............................. 99 Figure 1. Example Path Forwarding Nodes 101 In [RFC3168] it was recognized that tunnels and lower layer protocols 102 would need to support ECN, and ECN markings would need to be 103 propagated, as headers were encapsulated and decapsulated. 104 [ECNencapGuide] gives guidelines on the addition of ECN to protocols 105 like TRILL that often encapsulate IP packets, including propagation 106 of ECN from and to IP. 108 In the figure above, assuming IP traffic, RB1 is an encapsulator and 109 RB9 a decapsulator. Traffic from Source to RB1 might or might not get 110 marked as having experienced congestion in forwarding elements, such 111 as X, before being encapsulated at ingress RB1. Any such ECN marking 112 is encapsulated with a TRILL Header [RFC6325]. 114 This specification provides for any ECN marking in the traffic at the 115 ingress to be copied into the TRILL Extension Header Flags Word. It 116 also enables congestion marking by a congested RBridge such as RBn or 117 RB1 above in the TRILL Header Extension Flags Word [RFC7179]. 119 At RB9, the TRILL egress, it specifies how any ECN markings in the 120 TRILL Header Flags Word and in the encapsulated traffic are combined 121 so that subsequent forwarding elements, such as Y and the 122 Destination, can see if congestion was experienced at any previous 123 point in the path from Source. 125 A large part of the guidelines for adding ECN to lower layer 126 protocols [ECNencapGuide] concerns safe propagation of congestion 127 notifications in scenarios where some of the nodes do not support or 128 understand ECN. Such ECN ignorance is not a major problem with 129 RBridges using this specification because the method specified 130 assures that, if an egress RBridge is ECN ignorant (so it cannot 131 further propagate ECN) and congestion has been encountered, the 132 egress RBridge will at least drop the packet and this drop will 133 itself indicate congestion to end stations. 135 1.1 Conventions used in this document 137 The terminology and acronyms defined in [RFC6325] are used herein 138 with the same meaning. 140 In this documents, "IP" refers to both IPv4 and IPv6. 142 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 143 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 144 document are to be interpreted as described in [RFC2119] [RFC8174] 145 when, and only when, they appear in all capitals, as shown here. 147 Acronyms: 149 AQM - Active Queue Management 151 CCE - Critical Congestion Experienced 153 CE - Congestion Experienced 155 CItE - Critical Ingress-to-Egress 157 ECN - Explicit Congestion Notification 159 ECT - ECN Capable Transport 161 L4S - Low Latency, Low Loss, Scalable throughput 163 NCHbH - Non-Critical Hop-by-Hop 165 NCCE - Non-Critical Congestion Experienced 166 Not-ECT - Not ECN-Capable Transport 168 PCN - Pre-Congestion Notification 170 2. The ECN Specific Extended Header Flags 172 The extension header fields for explicit congestion notification 173 (ECN) in TRILL are defined as a two-bit TRILL-ECN field and a one-bit 174 Critical Congestion Experienced (CCE) field in the 32-bit TRILL 175 Header Extension Flags Word [RFC7780]. 177 These fields are show in Figure 2 as "ECN" and "CCE". The TRILL-ECN 178 field consists of bits 12 and 13, which are in the range reserved for 179 non-critical hop-by-hop (NCHbH) bits. The CCE field consists of bit 180 26, which is in the range reserved for Critical Ingress-to-Egress 181 (CItE) bits. The CRItE bit is the critical Ingress-to-Egress summary 182 bit and will be one if and only if any of the bits in the CItE range 183 (21-26) is one or there is a critical feature invoked in some further 184 extension of the TRILL Header after the Extesnion Flags Word. The 185 other bits and fields shown in Figure 2 are not relevant to ECN. See 186 [RFC7780], [RFC7179], and [IANAthFlags] for the meaning of these 187 other bits and fields. 189 0 1 2 3 190 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 1 191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 192 |Crit.| CHbH | NCHbH |CRSV | NCRSV | CItE | NCItE | 193 |.....|.........|...........|.....|.......|...........|.........| 194 |C|C|C| |C|N| | | | | | | | | 195 |R|R|R| |R|C| |ECN| Ext | | |C|Ext| | 196 |H|I|R| |C|C| | | Hop | | |C|Clr| | 197 |b|t|s| |A|A| | | Cnt | | |E| | | 198 |H|E|v| |F|F| | | | | | | | | 199 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 201 Figure 2 The ECN and CCE TRILL Header Extension Flags Word Fields 203 Table 1 shows the meaning of the codepoints in the TRILL-ECN field. 204 The first three have the same meaning as the corresponding ECN field 205 codepoints in the IPv4 or IPv6 header as defined in [RFC3168]. 206 However codepoint 0b11 is called Non-Critical Congestion Experienced 207 (NCCE) to distinguish it from Congestion Experienced in IP. 209 Binary Name Meaning 210 ------ ------- ----------------------------------- 211 00 Not-ECT Not ECN-Capable Transport 212 01 ECT(1) ECN-Capable Transport (1) 213 10 ECT(0) ECN-Capable Transport (0) 214 11 NCCE Non-Critical Congestion Experienced 216 Table 1. TRILL-ECN Field Codepoints 218 3. ECN Support 220 The subsections below describe the required behavior to support ECN 221 at TRILL ingress, transit, and egress. The ingress behavior occurs as 222 a native frame is encapsulated with a TRILL Header to produce a TRILL 223 Data packet. The transit behavior occurs in all RBridges where TRILL 224 Data packets are queued, usually at the output port. The egress 225 behavior occurs where a TRILL Data packet is decapsulated and output 226 as a native frame through an RBridge port. 228 An RBridge that supports ECN MUST behave as described in the relevant 229 subsections below, which correspond to the recommended provisions of 230 [ECNencapGuide]. Nonetheless, the scheme is designed to safely 231 propagate some form of congestion notification even if some RBridges 232 in the path followed by a TRILL Data packet support ECN and others do 233 not. 235 3.1 Ingress ECN Support 237 The behavior at an ingress RBridge is as follows: 239 o When encapsulating an IP frame, the ingress RBridge MUST: 241 + set the F flag in the main TRILL header [RFC7780]; 242 + create a Flags Word as part of the TRILL Header; 243 + copy the two ECN bits from the IP header into the TRILL-ECN 244 field (Flags Word bits 12 and 13) 245 + ensure the CCE flag is set to zero (Flags Word bit 26). 247 o When encapsulating a frame for a non-IP protocol, where that 248 protocol has a means of indicating ECN that is understood by the 249 ingress RBridge, it MUST follow the guidelines in [ECNencapGuide] 250 to add a Flags Word to the TRILL Header. For a non-IP protocol 251 with a similar ECN field to IP, this would be achieved by copying 252 into the TRILL-ECN field from the encapsulated native frame. 254 3.2 Transit ECN Support 256 The transit behavior, shown below, is required at all RBridges where 257 TRILL Data packets are queued, usually at the output port. 259 o An RBridge that supports ECN MUST implement some form of active 260 queue management (AQM) according to the guidelines of [RFC7567]. 261 The RBridge detects congestion either by monitoring its own queue 262 depth or by participating in a link-specific protocol. 264 o If the TRILL Header Flags Word is present, whenever the AQM 265 algorithm decides to indicate congestion on a TRILL Data packet it 266 MUST set the CCE flag (Flags Word bit 26). 268 o If the TRILL header Flags Word is not present, to indicate 269 congestion the RBridge will either drop the packet or it MAY do 270 all of the following instead: 272 + set the F flag in the main TRILL header; 273 + add a Flags Word to the TRILL Header; 274 + set the TRILL-ECN field to Not-ECT (00); 275 + and set the CCE flag and the Ingress-to-Egress critical summary 276 bit (CRIbE). 278 Note that a transit RBridge that supports ECN does not refer to the 279 TRILL-ECN field before signalling CCE in a packet. It signals CCE 280 irrespective of whether the packet indicates that the transport is 281 ECN-capable. The egress/decapsulation behavior (described next) 282 ensures that a CCE indication is converted to a drop if the transport 283 is not ECN-capable. 285 3.3 Egress ECN Support 287 If the egress RBridge does not support ECN, that RBridge will ignore 288 bits 12 and 13 of any Flags Word that is present, because it does not 289 contain any special ECN logic. Nonetheless, if a transit RBridge has 290 set the CCE flag, the egress will drop the packet. This is because 291 drop is the default behavior for an RBridge decapsulating a Critical 292 Ingress-to-Egress flag when it has no specific logic to understand 293 it. Drop is the intended behavior for such a packet, as required by 294 [ECNencapGuide]. 296 If an RBridge supports ECN, the egress behavior is as follows: 298 o When decapsulating an inner IP packet, the RBridge sets the ECN 299 field of the outgoing native IP packet using Table 2. It MUST set 300 the ECN field of the outgoing IP packet to the codepoint at the 301 intersection of the row for the arriving encapsulated IP packet 302 and the column for 3-bit ECN codepoint in the arriving outer TRILL 303 Data packet TRILL Header. If no TRILL Header Extension Flags Word 304 is present, the 3-bit ECN codepoint is assumed to be all zero 305 bits. 306 The name of the TRILL 3-bit ECN codepoint is defined using the 307 combination of the TRILL-ECN and CCE fields in Table 3. 308 Specifically, the TRILL 3-bit ECN codepoint is called CE if either 309 NCCE or CCE is set in the TRILL Header Extension Flags Word. 310 Otherwise it has the same name as the 2-bit TRILL-ECN codepoint. 311 In the case where the TRILL 3-bit ECN codepoint indicates 313 congestion experienced (CE) but the encapsulated native IP frame 314 indicates a not ECN-capable transport (Not-ECT), the RBridge MUST 315 drop the packet. Such packet dropping is necessary because a 316 transport above the IP layer that is not ECN-capable will have no 317 ECN logic, so it will only understand dropped packets as an 318 indication of congestion. 320 o When decapsulating a non-IP protocol frame with a means of 321 indicating ECN that is understood by the RBridge, it MUST follow 322 the guideines in [ECNencapGuide] when setting the ECN information 323 in the decapsulated native frame. For a non-IP protocol with a 324 similar ECN field to IP, this would be achieved by combining the 325 information in the TRILL Header Flags Word with the encapsulated 326 non-IP native frame, as specified in Table 2. 328 +---------+----------------------------------------------+ 329 | Inner | Arriving TRILL 3-bit ECN Codepoint Name | 330 | Native +---------+------------+------------+----------+ 331 | Header | Not-ECT | ECT(0) | ECT(1) | CE | 332 +---------+---------+------------+------------+----------+ 333 | Not-ECT | Not-ECT | Not-ECT(*) | Not-ECT(*) | | 334 | ECT(0) | ECT(0) | ECT(0) | ECT(1) | CE | 335 | ECT(1) | ECT(1) | ECT(1)(*) | ECT(1) | CE | 336 | CE | CE | CE | CE(*) | CE | 337 +---------+---------+------------+------------+----------+ 339 Table 2: Egress ECN Behavior 341 An asterisk in the above table indicates a currently unused 342 combination that SHOULD be logged. In contrast to [RFC6040], in TRILL 343 the drop condition is the result of a valid combination of events and 344 need not be logged. 346 +------------+-----+---------------------+ 347 | TRILL-ECN | CCE | Arriving TRILL 3-bit| 348 | | | ECN codepoint name | 349 +------------+-----+---------------------+ 350 | Not-ECT 00 | 0 | Not-ECT | 351 | ECT(1) 01 | 0 | ECT(1) | 352 | ECT(0) 10 | 0 | ECT(0) | 353 | NCCE 11 | 0 | CE | 354 | Not-ECT 00 | 1 | CE | 355 | ECT(1) 01 | 1 | CE | 356 | ECT(0) 10 | 1 | CE | 357 | NCCE 11 | 1 | CE | 358 +------------+-----+---------------------+ 360 Table 3: Mapping of TRILL-ECN and CCE Fields to TRILL 3-bit ECN 361 Codepoint Name 363 4. TRILL Support for ECN Variants 365 This section is informative, not normative. 367 Section 3 specifies interworking between TRILL and the original 368 standardized form of ECN in IP [RFC3168]. 370 The ECN wire protocol for TRILL (Section 2) has been designed to 371 support the other known variants of ECN, as detailed below. New 372 variants of ECN will have to comply with the guidelines for defining 373 alternative ECN semantics [RFC4774]. It is expected that the TRILL 374 ECN wire protocol is generic enough to support such potential future 375 variants. 377 4.1 Pre-Congestion Notification (PCN) 379 The PCN wire protocol [RFC6660] is recognised by the use of a PCN- 380 compatible Diffserv codepoint in the IP header and a non-zero IP-ECN 381 field. For TRILL or any lower layer protocol, equivalent traffic 382 classification codepoints would have to be defined, but that is 383 outside the scope of the current document. 385 The PCN wire protocol is similar to ECN, except it indicates 386 congestion with two levels of severity. It uses: 388 o 11 (CE) as the most severe, termed the Excess-traffic-marked (ETM) 389 codepoint 391 o 01 ECT(1) as a lesser severity level, termed the Threshold-Marked 392 (ThM) codepoint. (This difference between ECT(1) and ECT(0) only 393 applies to PCN, not to the classic ECN support specified for TRILL 394 in this document before Section 4.) 396 To implement PCN on a transit RBridge would require a detailed 397 specification. But in brief: 399 o the TRILL Critical Congestion Experienced (CCE) flag would be used 400 for the Excess-Traffic-Marked (ETM) codepoint; 402 o ECT(1) in the TRILL-ECN field would be used for the Threshold- 403 Marked codepoint. 405 Then the ingress and egress behaviors defined in Section 3 would not 406 need to be altered to ensure support for PCN as well as ECN. 408 4.2 Low Latency, Low Loss, Scalable Throughput (L4S) 410 L4S is currently on the IETF's experimental track. An outline of how 411 a transit TRILL RBridge would support L4S [ECNL4S] is given in 412 Appendix A. 414 5. IANA Considerations 416 IANA is requested to update the TRILL Extended Header Flags registry 417 by replacing the lines for bits 9-13 and for bits 21-26 with the 418 following: 420 Bits Purpose Reference 421 ----- ------- --------- 422 9-11 available non-critical hop-by-hop flags 423 12-13 TRILL-ECN (Explicit Congestion Notification) [this doc] 425 21-25 available critical ingress-to-egress flags 426 26 Critical Congestion Experienced (CCE) [this doc] 428 6. Security Considerations 430 TRILL support of ECN is a straight forward combination of previously 431 specified ECN and TRILL with no significnat new security 432 considerations. 434 For ECN tunneling security considerations, see [RFC6040]. 436 For general TRILL protocol security considerations, see [RFC6325]. 438 7. Acknowledgements 440 The helpful comments of Loa Andersson are hereby acknowledged. 442 This document was prepared with basic NROFF. All macros used were 443 defined in the source file. 445 Normative References 447 [RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate 448 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, 449 March 1997, . 451 [RFC3168] - Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 452 of Explicit Congestion Notification (ECN) to IP", RFC 3168, DOI 453 10.17487/RFC3168, September 2001, . 456 [RFC4774] - Floyd, S., "Specifying Alternate Semantics for the 457 Explicit Congestion Notification (ECN) Field", BCP 124, RFC 458 4774, DOI 10.17487/RFC4774, November 2006, . 461 [RFC6325] - Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A. 462 Ghanwani, "Routing Bridges (RBridges): Base Protocol 463 Specification", RFC 6325, DOI 10.17487/RFC6325, July 2011, 464 . 466 [RFC7179] - Eastlake 3rd, D., Ghanwani, A., Manral, V., Li, Y., and 467 C. Bestler, "Transparent Interconnection of Lots of Links 468 (TRILL): Header Extension", RFC 7179, DOI 10.17487/RFC7179, May 469 2014, . 471 [RFC7567] - Baker, F., Ed., and G. Fairhurst, Ed., "IETF 472 Recommendations Regarding Active Queue Management", BCP 197, 473 RFC 7567, DOI 10.17487/RFC7567, July 2015, . 476 [RFC7780] - Eastlake 3rd, D., Zhang, M., Perlman, R., Banerjee, A., 477 Ghanwani, A., and S. Gupta, "Transparent Interconnection of 478 Lots of Links (TRILL): Clarifications, Corrections, and 479 Updates", RFC 7780, DOI 10.17487/RFC7780, February 2016, 480 . 482 [RFC8174] - Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 483 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 484 2017, 486 [ECNencapGuide] - B. Briscoe, J. Kaippallimalil, P. Thaler, 487 "Guidelines for Adding Congestion Notification to Protocols 488 that Encapsulate IP", draft-ietf-tsvwg-ecn-encap-guidelines, 489 work in progress. 491 Informative References 493 [ECNL4S] - K. De Schepper, B. Briscoe, "Identifying Modified Explicit 494 Congestion Notification (ECN) Semantics for Ultra-Low Queueing 495 Delay", draft-ietf-tsvwg-ecn-l4s-id, work in progress. 497 [IANAthFlags] - IANA TRILL Extended Header word flags: 498 http://www.iana.org/assignments/trill-parameters/trill- 499 parameters.xhtml#extended-header-flags 501 [RFC6040] - Briscoe, B., "Tunnelling of Explicit Congestion 502 Notification", RFC 6040, DOI 10.17487/RFC6040, November 2010, 503 . 505 [RFC6660] - Briscoe, B., Moncaster, T., and M. Menth, "Encoding Three 506 Pre-Congestion Notification (PCN) States in the IP Header Using 507 a Single Diffserv Codepoint (DSCP)", RFC 6660, DOI 508 10.17487/RFC6660, July 2012, . 511 Appendix A. TRILL Transit RBridge Behavior to Support L4S 513 The specification of the Low Latency, Low Loss, Scalable throughput 514 (L4S) wire protocol for IP is given in [ECNL4S]. It is similar to the 515 original ECN wire protoocl for IP [RFC3168], except: 517 o An AQM that supports L4S classifies packets with ECT(1) or CE in 518 the IP header into an L4S queue and a "Classic" queue otherwise. 520 o the meaning of CE markings applied by an L4S queue is not the same 521 as the meaning of a drop by a "Classic" queue (contrary to the 522 original requirement for ECN [RFC3168]). Instead the likelihood 523 that the Classic queue drops packets is defined as the square of 524 the likelihood that the L4S queue marks packets (e.g. when there 525 is a drop probability of 0.0009 (0.09%) the L4S marking 526 probability will be 0.03 (3%)). 528 This seems to present a problem for the way that a transit TRILL 529 RBridge defers the choice between marking and dropping to the egress. 530 Nonetheless, the following pseudocode outlines how a transit TRILL 531 RBridge can implement L4S marking in such a way that the egress 532 behavior already described in Section 3.3 for Classic ECN [RFC3168] 533 will produce the desired outcome. 535 /* p is an internal variable calculated by any L4S AQM 536 * dependent on the delay being experienced in the Classic queue. 537 * bit13 is the least significant bit of the TRILL-ECN field 538 */ 540 % On TRILL transit 541 if (bit13 == 0 ) { 542 % Classic Queue 543 if (p > max(random(), random()) ) 544 mark(CCE) % likelihood: p^2 546 } else { 547 % L4S Queue 548 if (p > random() ) { 549 if (p > random() ) 550 mark(CCE) % likelihood: p^2 551 else 552 mark(NCCE) % likelihood: p - p^2 553 } 554 } 556 With the above transit behavior, an egress that supports ECN (Section 557 3.3) will drop packets or propagate their ECN markings depending on 558 whether the arriving inner header is from a non-ECN-capable or ECN- 559 capable transport. 561 Even if an egress has no L4S-specific logic of its own, it will drop 562 packets with the square of the probability that an egress would if it 563 did support ECN, for the following reasons: 565 o Egress with ECN support: 567 + L4S: propagates both the Critical and Non-Critical CE marks 568 (CCE & NCCE) as a CE mark. 570 Likelihood: p^2 + p - p^2 = p 572 + Classic: Propagates CCE marks as CE or drop, depending on 573 inner. 575 Likelihood: p^2 577 o Egress without ECN support: 579 + L4S: does not propagate NCCE as a CE mark, but drops CCE marks. 581 Likelihood: p^2 583 + Classic: drops CCE marks. 585 Likelihood: p^2 587 Authors' Addresses 589 Donald E. Eastlake, 3rd 590 Huawei Technologies 591 155 Beaver Street 592 Milford, MA 01757 USA 594 Tel: +1-508-333-2270 595 Email: d3e3e3@gmail.com 597 Bob Briscoe 598 Simula Research Lab 600 Email: ietf@bobbriscoe.net 601 URI: http://bobbriscoe.net/ 603 Copyright and IPR Provisions 605 Copyright (c) 2017 IETF Trust and the persons identified as the 606 document authors. All rights reserved. 608 This document is subject to BCP 78 and the IETF Trust's Legal 609 Provisions Relating to IETF Documents 610 (http://trustee.ietf.org/license-info) in effect on the date of 611 publication of this document. Please review these documents 612 carefully, as they describe your rights and restrictions with respect 613 to this document. Code Components extracted from this document must 614 include Simplified BSD License text as described in Section 4.e of 615 the Trust Legal Provisions and are provided without warranty as 616 described in the Simplified BSD License. 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