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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFCXXXX' is mentioned on line 581, but not defined == Missing Reference: 'LE-PHB' is mentioned on line 510, but not defined == Missing Reference: 'RFC7657' is mentioned on line 587, but not defined ** Downref: Normative reference to an Informational RFC: RFC 2475 -- Obsolete informational reference (is this intentional?): RFC 3662 (Obsoleted by RFC 8622) Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force R. Bless 3 Internet-Draft Karlsruhe Institute of Technology (KIT) 4 Obsoletes: 3662 (if approved) October 11, 2018 5 Updates: 4594,8325 (if approved) 6 Intended status: Standards Track 7 Expires: April 14, 2019 9 A Lower Effort Per-Hop Behavior (LE PHB) 10 draft-ietf-tsvwg-le-phb-06 12 Abstract 14 This document specifies properties and characteristics of a Lower 15 Effort (LE) per-hop behavior (PHB). The primary objective of this LE 16 PHB is to protect best-effort (BE) traffic (packets forwarded with 17 the default PHB) from LE traffic in congestion situations, i.e., when 18 resources become scarce, best-effort traffic has precedence over LE 19 traffic and may preempt it. Alternatively, packets forwarded by the 20 LE PHB can be associated with a scavenger service class, i.e., they 21 scavenge otherwise unused resources only. There are numerous uses 22 for this PHB, e.g., for background traffic of low precedence, such as 23 bulk data transfers with low priority in time, non time-critical 24 backups, larger software updates, web search engines while gathering 25 information from web servers and so on. This document recommends a 26 standard DSCP value for the LE PHB. This specification obsoletes RFC 27 3662 and updates the DSCP recommended in RFC 4594 and RFC 8325 to use 28 the DSCP assigned in this specification. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on April 14, 2019. 47 Copyright Notice 49 Copyright (c) 2018 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 This document may contain material from IETF Documents or IETF 63 Contributions published or made publicly available before November 64 10, 2008. The person(s) controlling the copyright in some of this 65 material may not have granted the IETF Trust the right to allow 66 modifications of such material outside the IETF Standards Process. 67 Without obtaining an adequate license from the person(s) controlling 68 the copyright in such materials, this document may not be modified 69 outside the IETF Standards Process, and derivative works of it may 70 not be created outside the IETF Standards Process, except to format 71 it for publication as an RFC or to translate it into languages other 72 than English. 74 Table of Contents 76 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 77 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 78 3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 3 79 4. PHB Description . . . . . . . . . . . . . . . . . . . . . . . 5 80 5. Traffic Conditioning Actions . . . . . . . . . . . . . . . . 6 81 6. Recommended DS Codepoint . . . . . . . . . . . . . . . . . . 6 82 7. Deployment Considerations . . . . . . . . . . . . . . . . . . 7 83 8. Remarking to other DSCPs/PHBs . . . . . . . . . . . . . . . . 8 84 9. Multicast Considerations . . . . . . . . . . . . . . . . . . 9 85 10. The Update to RFC 4594 . . . . . . . . . . . . . . . . . . . 10 86 11. The Update to RFC 8325 . . . . . . . . . . . . . . . . . . . 11 87 12. The Update to draft-ietf-tsvwg-rtcweb-qos . . . . . . . . . . 12 88 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 89 14. Security Considerations . . . . . . . . . . . . . . . . . . . 14 90 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 91 15.1. Normative References . . . . . . . . . . . . . . . . . . 14 92 15.2. Informative References . . . . . . . . . . . . . . . . . 14 93 Appendix A. History of the LE PHB . . . . . . . . . . . . . . . 17 94 Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . 17 95 Appendix C. Change History . . . . . . . . . . . . . . . . . . . 17 96 Appendix D. Note to RFC Editor . . . . . . . . . . . . . . . . . 19 97 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 19 99 1. Introduction 101 This document defines a Differentiated Services per-hop behavior 102 [RFC2474] called "Lower Effort" (LE), which is intended for traffic 103 of sufficiently low urgency that all other traffic takes precedence 104 over the LE traffic in consumption of network link bandwidth. Low 105 urgency traffic has a low priority for timely forwarding, which does 106 not necessarily imply that it is generally of minor importance. From 107 this viewpoint, it can be considered as a network equivalent to a 108 background priority for processes in an operating system. There may 109 or may not be memory (buffer) resources allocated for this type of 110 traffic. 112 Some networks carry traffic for which delivery is considered 113 optional; that is, packets of this type of traffic ought to consume 114 network resources only when no other traffic is present. In this 115 point of view, packets forwarded by the LE PHB scavenge otherwise 116 unused resources only, which led to the name "scavenger service" in 117 early Internet2 deployments (see Appendix A). Other commonly used 118 names for LE PHB type services are "Lower-than-best-effort" or "Less- 119 than-best-effort". Alternatively, the effect of this type of traffic 120 on all other network traffic is strictly limited ("no harm" 121 property). This is distinct from "best-effort" (BE) traffic since 122 the network makes no commitment to deliver LE packets. In contrast, 123 BE traffic receives an implied "good faith" commitment of at least 124 some available network resources. This document proposes a Lower 125 Effort Differentiated Services per-hop behavior (LE PHB) for handling 126 this "optional" traffic in a differentiated services node. 128 2. Requirements Language 130 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 131 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 132 "OPTIONAL" in this document are to be interpreted as described in BCP 133 14 [RFC2119] [RFC8174] when, and only when, they appear in all 134 capitals, as shown here. 136 3. Applicability 138 A Lower Effort PHB is applicable for many applications that otherwise 139 use best-effort delivery. More specifically, it is suitable for 140 traffic and services that can tolerate strongly varying throughput 141 for their data flows, especially periods of very low throughput or 142 even starvation (i.e., long interruptions due to significant or even 143 complete packet loss). Therefore, an application sending an LE 144 marked flow needs to be able to tolerate short or (even very) long 145 interruptions due to the presence of severe congestion conditions 146 during the transmission of the flow. Thus, there ought to be an 147 expectation that packets of the LE PHB could be excessively delayed 148 or dropped when any other traffic is present. The LE PHB is suitable 149 for sending traffic of low urgency across a Differentiated Services 150 (DS) domain or DS region. 152 Just like best-effort traffic, LE traffic SHOULD be congestion 153 controlled (i.e., use a congestion controlled transport or implement 154 an appropriate congestion control method [RFC8085]). Since LE 155 traffic could be starved completely for a longer period of time, 156 transport protocols or applications (and their related congestion 157 control mechanisms) SHOULD be able to detect and react to such a 158 situation and ought to resume the transfer as soon as possible. 159 Congestion control is not only useful to let the flows within the LE 160 behavior aggregate adapt to the available bandwidth that may be 161 highly fluctuating, but is also essential if LE traffic is mapped to 162 the default PHB in DS domains that do not support LE. 164 Use of the LE PHB might assist a network operator in moving certain 165 kinds of traffic or users to off-peak times. Alternatively, or in 166 addition, packets can be designated for the LE PHB when the goal is 167 to protect all other packet traffic from competition with the LE 168 aggregate while not completely banning LE traffic from the network. 169 An LE PHB SHOULD NOT be used for a customer's "normal Internet" 170 traffic nor should packets be "downgraded" to the LE PHB instead of 171 being dropped, particularly when the packets are unauthorized 172 traffic. The LE PHB is expected to have applicability in networks 173 that have at least some unused capacity at certain periods. 175 The LE PHB allows networks to protect themselves from selected types 176 of traffic as a complement to giving preferential treatment to other 177 selected traffic aggregates. LE ought not to be used for the general 178 case of downgraded traffic, but could be used by design, e.g., to 179 protect an internal network from untrusted external traffic sources. 180 In this case there is no way for attackers to preempt internal (non 181 LE) traffic by flooding. Another use case in this regard is 182 forwarding of multicast traffic from untrusted sources. Multicast 183 forwarding is currently enabled within domains only for specific 184 sources within a domain, but not for sources from anywhere in the 185 Internet. A main problem is that multicast routing creates traffic 186 sources at (mostly) unpredictable branching points within a domain, 187 potentially leading to congestion and packet loss. In the case of 188 multicast traffic packets from untrusted sources are forwarded as LE 189 traffic, they will not harm traffic from non-LE behavior aggregates. 191 A further related use case is mentioned in [RFC3754]: preliminary 192 forwarding of non-admitted multicast traffic. 194 There is no intrinsic reason to limit the applicability of the LE PHB 195 to any particular application or type of traffic. It is intended as 196 an additional traffic engineering tool for network administrators. 197 For instance, it can be used to fill protection capacity of 198 transmission links that is otherwise unused. Some network providers 199 keep link utilization below 50% to ensure that all traffic is 200 forwarded without loss after rerouting caused by a link failure (cf. 201 Section 6 of [RFC3439]). LE marked traffic can utilize the normally 202 unused capacity and will be preempted automatically in case of link 203 failure when 100% of the link capacity is required for all other 204 traffic. Ideally, applications mark their packets as LE traffic, 205 since they know the urgency of flows. 207 Example uses for the LE PHB: 209 o For traffic caused by world-wide web search engines while they 210 gather information from web servers. 212 o For software updates or dissemination of new releases of operating 213 systems. 215 o For reporting errors or telemetry data from operating systems or 216 applications. 218 o For backup traffic or non-time critical synchronization or 219 mirroring traffic. 221 o For content distribution transfers between caches. 223 o For preloading or prefetching objects from web sites. 225 o For network news and other "bulk mail" of the Internet. 227 o For "downgraded" traffic from some other PHB when this does not 228 violate the operational objectives of the other PHB. 230 o For multicast traffic from untrusted (e.g., non-local) sources. 232 4. PHB Description 234 The LE PHB is defined in relation to the default PHB (best-effort). 235 A packet forwarded with the LE PHB SHOULD have lower precedence than 236 packets forwarded with the default PHB, i.e., in the case of 237 congestion, LE marked traffic SHOULD be dropped prior to dropping any 238 default PHB traffic. Ideally, LE packets SHOULD be forwarded only if 239 no packet with any other PHB is awaiting transmission. 241 A straightforward implementation could be a simple priority scheduler 242 serving the default PHB queue with higher priority than the lower- 243 effort PHB queue. Alternative implementations may use scheduling 244 algorithms that assign a very small weight to the LE class. This, 245 however, could sometimes cause better service for LE packets compared 246 to BE packets in cases when the BE share is fully utilized and the LE 247 share not. 249 If a dedicated LE queue is not available, an active queue management 250 mechanism within a common BE/LE queue could also be used. This could 251 drop all arriving LE packets as soon as certain queue length or 252 sojourn time thresholds are exceeded. 254 Since congestion control is also useful within the LE traffic class, 255 Explicit Congestion Notification [RFC3168] SHOULD be used for LE 256 packets, too. 258 5. Traffic Conditioning Actions 260 If possible, packets SHOULD be pre-marked in DS-aware end systems by 261 applications due to their specific knowledge about the particular 262 precedence of packets. There is no incentive for DS domains to 263 distrust this initial marking, because letting LE traffic enter a DS 264 domain causes no harm. Thus, any policing such as limiting the rate 265 of LE traffic is not necessary at the DS boundary. 267 As for most other PHBs an initial classification and marking can be 268 also performed at the first DS boundary node according to the DS 269 domain's own policies (e.g., as protection measure against untrusted 270 sources). However, non-LE traffic (e.g., BE traffic) SHOULD NOT be 271 remarked to LE on a regular basis without consent or knowledge of the 272 user. See also remarks with respect to downgrading in Section 3 and 273 Section 8. 275 6. Recommended DS Codepoint 277 The RECOMMENDED codepoint for the LE PHB is '000001'. 279 Earlier specifications [RFC4594] recommended to use CS1 as codepoint 280 (as mentioned in [RFC3662]). This is problematic since it may cause 281 a priority inversion in DiffServ domains that treat CS1 as originally 282 proposed in [RFC2474], resulting in forwarding LE packets with higher 283 precedence than BE packets. Existing implementations SHOULD 284 transition to use the unambiguous LE codepoint '000001' whenever 285 possible. 287 This particular codepoint was chosen due to measurements on the 288 currently observable DSCP remarking behavior in the Internet 289 [ietf99-secchi]. Since some network domains set the former IP 290 precedence bits to zero, it is possible that some other standardized 291 DSCPs get mapped to the LE PHB DSCP if it were taken from the DSCP 292 standards action pool 1 (xxxxx0). 294 7. Deployment Considerations 296 In order to enable LE support, DS nodes typically only need 298 o A BA classifier (Behavior Aggregate classifier, see [RFC2475]) 299 that classifies packets according to the LE DSCP 301 o A dedicated LE queue 303 o A suitable scheduling discipline, e.g., simple priority queueing 305 Alternatively, implementations could use active queue management 306 mechanisms instead of a dedicated LE queue, e.g., dropping all 307 arriving LE packets when certain queue length or sojourn time 308 thresholds are exceeded. 310 Internet-wide deployment of the LE PHB is eased by the following 311 properties: 313 o No harm to other traffic: since the LE PHB has the lowest 314 forwarding priority it does not consume resources from other PHBs. 315 Deployment across different provider domains with LE support 316 causes no trust issues or attack vectors to existing (non LE) 317 traffic. Thus, providers can trust LE markings from end-systems, 318 i.e., there is no need to police or remark incoming LE traffic. 320 o No PHB parameters or configuration of traffic profiles: the LE PHB 321 itself possesses no parameters that need to be set or configured. 322 Similarly, since LE traffic requires no admission or policing, it 323 is not necessary to configure traffic profiles. 325 o No traffic conditioning mechanisms: the LE PHB requires no traffic 326 meters, droppers, or shapers. See also Section 5 for further 327 discussion. 329 Operators of DS domains that cannot or do not want to support the LE 330 PHB should be aware that they violate the "no harm" property of LE. 331 DS domains that do not offer support for the LE PHB support SHOULD 332 NOT drop packets marked with the LE DSCP. They SHOULD map packets 333 with this DSCP to the default PHB and SHOULD preserve the LE DSCP 334 marking. See also Section 8 for further discussion of forwarding LE 335 traffic with the default PHB instead. 337 8. Remarking to other DSCPs/PHBs 339 "DSCP bleaching", i.e., setting the DSCP to '000000' (default PHB) is 340 NOT RECOMMENDED for this PHB. This may cause effects that are in 341 contrast to the original intent in protecting BE traffic from LE 342 traffic (no harm property). In the case that a DS domain does not 343 support the LE PHB, its nodes SHOULD treat LE marked packets with the 344 default PHB instead (by mapping the LE DSCP to the default PHB), but 345 they SHOULD do so without remarking to DSCP '000000'. The reason for 346 this is that later traversed DS domains may then have still the 347 possibility to treat such packets according to the LE PHB. 349 Operators of DS domains that forward LE traffic within the BE 350 aggregate need to be aware of the implications, i.e., induced 351 congestion situations and quality-of-service degradation of the 352 original BE traffic. In this case, the LE property of not harming 353 other traffic is no longer fulfilled. To limit the impact in such 354 cases, traffic policing of the LE aggregate MAY be used. 356 In case LE marked packets are effectively carried within the default 357 PHB (i.e., forwarded as best-effort traffic) they get a better 358 forwarding treatment than expected. For some applications and 359 services, it is favorable if the transmission is finished earlier 360 than expected. However, in some cases it may be against the original 361 intention of the LE PHB user to strictly send the traffic only if 362 otherwise unused resources are available. In case LE traffic is 363 mapped to the default PHB, LE traffic may compete with BE traffic for 364 the same resources and thus adversely affect the original BE 365 aggregate. Applications that want to ensure the lower precedence 366 compared to BE traffic even in such cases SHOULD use additionally a 367 corresponding Lower-than-Best-Effort transport protocol [RFC6297], 368 e.g., LEDBAT [RFC6817]. 370 A DS domain that still uses DSCP CS1 for marking LE traffic 371 (including Low Priority-Data as defined in [RFC4594] or the old 372 definition in [RFC3662]) SHOULD remark traffic to the LE DSCP 373 '000001' at the egress to the next DS domain. This increases the 374 probability that the DSCP is preserved end-to-end, whereas a CS1 375 marked packet may be remarked by the default DSCP if the next domain 376 is applying DiffServ-intercon [RFC8100]. 378 9. Multicast Considerations 380 Basically the multicast considerations in [RFC3754] apply. However, 381 using the Lower Effort PHB for multicast requires to pay special 382 attention to the way how packets get replicated inside routers. Due 383 to multicast packet replication, resource contention may actually 384 occur even before a packet is forwarded to its output port and in the 385 worst case, these forwarding resources are missing for higher 386 prioritized multicast or even unicast packets. 388 Several forwarding error correction coding schemes such as fountain 389 codes (e.g., [RFC5053]) allow reliable data delivery even in 390 environments with a potential high amount of packet loss in 391 transmission. When used for example over satellite links or other 392 broadcast media, this means that receivers that loose 80% of packets 393 in transmission simply need 5 times as long to receive the complete 394 data than those receivers experiencing no loss (without any receiver 395 feedback required). 397 Superficially viewed, it may sound very attractive to use IP 398 multicast with the LE PHB to build this type of opportunistic 399 reliable distribution in IP networks, but it can only be usefully 400 deployed with routers that do not experience forwarding/replication 401 resource starvation when a large amount of packets (virtually) need 402 to be replicated to links where the LE queue is full. 404 Thus, packet replication of LE marked packets should consider the 405 situation at the respective output links: it is a waste of internal 406 forwarding resources if a packet is replicated to output links that 407 have no resources left for LE forwarding. In those cases a packet 408 would have been replicated just to be dropped immediately after 409 finding a filled LE queue at the respective output port. Such 410 behavior could be avoided for example by using a conditional internal 411 packet replication: a packet would then only be replicated in case 412 the output link is not fully used. This conditional replication, 413 however, is probably not widely implemented. 415 While the resource contention problem caused by multicast packet 416 replication is also true for other DiffServ PHBs, LE forwarding is 417 special, because often it is assumed that LE packets get only 418 forwarded in case of available resources at the output ports. The 419 previously mentioned redundancy data traffic could nicely use the 420 varying available residual bandwidth being utilized the by LE PHB, 421 but only if the previously specific requirements in the internal 422 implementation of the network devices are considered. 424 10. The Update to RFC 4594 426 [RFC4594] recommended to use CS1 as codepoint in section 4.10, 427 whereas CS1 was defined in [RFC2474] to have a higher precedence than 428 CS0, i.e., the default PHB. Consequently, DiffServ domains 429 implementing CS1 according to [RFC2474] will cause a priority 430 inversion for LE packets that contradicts with the original purpose 431 of LE. Therefore, every occurrence of the CS1 DSCP is replaced by 432 the LE DSCP. 434 Changes: 436 o This update to RFC 4594 removes the following entry from figure 3: 438 |---------------+---------+-------------+--------------------------| 439 | Low-Priority | CS1 | 001000 | Any flow that has no BW | 440 | Data | | | assurance | 441 ------------------------------------------------------------------ 443 and replaces this by the following entry: 445 |---------------+---------+-------------+--------------------------| 446 | Low-Priority | LE | 000001 | Any flow that has no BW | 447 | Data | | | assurance | 448 ------------------------------------------------------------------ 450 o This update to RFC 4594 extends the Notes text below figure 3 that 451 currently states "Notes for Figure 3: Default Forwarding (DF) and 452 Class Selector 0 (CS0) provide equivalent behavior and use the 453 same DS codepoint, '000000'." to state "Notes for Figure 3: 454 Default Forwarding (DF) and Class Selector 0 (CS0) provide 455 equivalent behavior and use the same DS codepoint, '000000'. The 456 prior recommendation to use the CS1 DSCP for Low-Priority Data has 457 been replaced by the current recommendation to use the LE DSCP, 458 '000001'." 460 o This update to RFC 4594 removes the following entry from figure 4: 462 |---------------+------+-------------------+---------+--------+----| 463 | Low-Priority | CS1 | Not applicable | RFC3662 | Rate | Yes| 464 | Data | | | | | | 465 ------------------------------------------------------------------ 467 and replaces this by the following entry: 469 |---------------+------+-------------------+---------+--------+----| 470 | Low-Priority | LE | Not applicable | RFCXXXX | Rate | Yes| 471 | Data | | | | | | 472 ------------------------------------------------------------------ 474 o Section 2.3 of [RFC4594] specifies: "In network segments that use 475 IP precedence marking, only one of the two service classes can be 476 supported, High-Throughput Data or Low-Priority Data. We 477 RECOMMEND that the DSCP value(s) of the unsupported service class 478 be changed to 000xx1 on ingress and changed back to original 479 value(s) on egress of the network segment that uses precedence 480 marking. For example, if Low-Priority Data is mapped to Standard 481 service class, then 000001 DSCP marking MAY be used to distinguish 482 it from Standard marked packets on egress." This document removes 483 this recommendation, because by using the herein defined LE DSCP 484 such remarking is not necessary. So even if Low-Priority Data is 485 unsupported (i.e., mapped to the default PHB) the LE DSCP should 486 be kept across the domain as RECOMMENDED in Section 8. That 487 removed text is replaced by: "In network segments that use IP 488 Precedence marking, the Low-Priority Data service class receives 489 the same Diffserv QoS as the Standard service class when the LE 490 DSCP is used for Low-Priority Data traffic. This is acceptable 491 behavior for the Low-Priority Data service class, although it is 492 not the preferred behavior." 494 o This document removes the following line of RFC 4594, 495 Section 4.10: "The RECOMMENDED DSCP marking is CS1 (Class Selector 496 1)." and replaces this with the following text: "The RECOMMENDED 497 DSCP marking is LE (Lower Effort), which replaces the prior 498 recommendation for CS1 (Class Selector 1) marking." 500 11. The Update to RFC 8325 502 Section 4.2.10 of RFC 8325 [RFC8325] specifies "[RFC3662] and 503 [RFC4594] both recommend Low-Priority Data be marked CS1 DSCP." 504 which is updated to "[RFC3662] recommends that Low-Priority Data be 505 marked CS1 DSCP. [RFC4594] as updated by [RFCXXXX] recommends Low- 506 Priority Data be marked LE DSCP." 508 This document removes the following paragraph of RFC 8325, 509 Section 4.2.10 because this document makes the anticipated change: 510 "Note: This marking recommendation may change in the future, as [LE- 511 PHB] defines a Lower Effort (LE) PHB for Low-Priority Data traffic 512 and recommends an additional DSCP for this traffic." 514 Section 4.2.10 of RFC 8325 [RFC8325] specifies "therefore, it is 515 RECOMMENDED to map Low-Priority Data traffic marked CS1 DSCP to UP 1" 516 which is updated to "therefore, it is RECOMMENDED to map Low-Priority 517 Data traffic marked with LE DSCP or legacy CS1 DSCP to UP 1" 519 This update to RFC 8325 replaces the following entry from figure 1: 521 +---------------+------+----------+-------------+--------------------+ 522 | Low-Priority | CS1 | RFC 3662 | 1 | AC_BK (Background) | 523 | Data | | | | | 524 +--------------------------------------------------------------------+ 526 by the following entries: 528 +---------------+------+----------+-------------+--------------------+ 529 | Low-Priority | LE | RFCXXXX | 1 | AC_BK (Background) | 530 | Data | | | | | 531 +--------------------------------------------------------------------+ 532 | Low-Priority | CS1 | RFC 3662 | 1 | AC_BK (Background) | 533 | Data (legacy) | | | | | 534 +--------------------------------------------------------------------+ 536 12. The Update to draft-ietf-tsvwg-rtcweb-qos 538 Section 5 of [I-D.ietf-tsvwg-rtcweb-qos] describes the Recommended 539 DSCP Values for WebRTC Applications 541 This update to [I-D.ietf-tsvwg-rtcweb-qos] replaces all occurences of 542 CS1 with LE in Table 1: 544 +------------------------+-------+------+-------------+-------------+ 545 | Flow Type | Very | Low | Medium | High | 546 | | Low | | | | 547 +------------------------+-------+------+-------------+-------------+ 548 | Audio | LE | DF | EF (46) | EF (46) | 549 | | (1) | (0) | | | 550 | | | | | | 551 | Interactive Video with | LE | DF | AF42, AF43 | AF41, AF42 | 552 | or without Audio | (1) | (0) | (36, 38) | (34, 36) | 553 | | | | | | 554 | Non-Interactive Video | LE | DF | AF32, AF33 | AF31, AF32 | 555 | with or without Audio | (1) | (0) | (28, 30) | (26, 28) | 556 | | | | | | 557 | Data | LE | DF | AF11 | AF21 | 558 | | (1) | (0) | | | 559 +------------------------+-------+------+-------------+-------------+ 561 and updates the following paragraph: 563 "The above table assumes that packets marked with CS1 are treated as 564 "less than best effort", such as the LE behavior described in 565 [RFC3662]. However, the treatment of CS1 is implementation 566 dependent. If an implementation treats CS1 as other than "less than 567 best effort", then the actual priority (or, more precisely, the per- 568 hop-behavior) of the packets may be changed from what is intended. 569 It is common for CS1 to be treated the same as DF, so applications 570 and browsers using CS1 cannot assume that CS1 will be treated 571 differently than DF [RFC7657]. However, it is also possible per 572 [RFC2474] for CS1 traffic to be given better treatment than DF, thus 573 caution should be exercised when electing to use CS1. This is one of 574 the cases where marking packets using these recommendations can make 575 things worse." 577 as follows: 579 "The above table assumes that packets marked with LE are treated as 580 lower effort (i.e., "less than best effort"), such as the LE behavior 581 described in [RFCXXXX]. However, the treatment of LE is 582 implementation dependent. If an implementation treats LE as other 583 than "less than best effort", then the actual priority (or, more 584 precisely, the per- hop-behavior) of the packets may be changed from 585 what is intended. It is common for LE to be treated the same as DF, 586 so applications and browsers using LE cannot assume that LE will be 587 treated differently than DF [RFC7657]. During development of this 588 document, the CS1 DSCP was recommended for "very low" application 589 priority traffic; implementations that followed that recommendation 590 SHOULD be updated to use the LE DSCP instead of the CS1 DSCP." 592 13. IANA Considerations 594 This document assigns the Differentiated Services Field Codepoint 595 (DSCP) '000001' from the Differentiated Services Field Codepoints 596 (DSCP) registry (https://www.iana.org/assignments/dscp-registry/dscp- 597 registry.xhtml) (Pool 3, Codepoint Space xxxx01, Standards Action) to 598 the LE PHB. This document suggests to use a DSCP from Pool 3 in 599 order to avoid problems for other PHB marked flows to become 600 accidentally remarked as LE PHB, e.g., due to partial DSCP bleaching. 601 See [I-D.ietf-tsvwg-iana-dscp-registry] for the request to re- 602 classify Pool 3 for Standards Action. 604 IANA is requested to update the registry as follows: 606 o Name: LE 608 o Value (Binary): 000001 610 o Value (Decimal): 1 611 o Reference: [RFC number of this memo] 613 14. Security Considerations 615 There are no specific security exposures for this PHB. Since it 616 defines a new class of low forwarding priority, remarking other 617 traffic as LE traffic may lead to quality-of-service degradation of 618 such traffic. Thus, any attacker that is able to modify the DSCP of 619 a packet to LE may carry out a downgrade attack. See the general 620 security considerations in [RFC2474] and [RFC2475]. 622 With respect to privacy, an attacker could use the information from 623 the DSCP to infer that the transferred (probably even encrypted) 624 content is considered of low priority or low urgency by a user, in 625 case the DSCP was set on the user's request. However, this disclosed 626 information is only useful if some form of identification happened at 627 the same time, see [RFC6973] for further details on general privacy 628 threats. 630 15. References 632 15.1. Normative References 634 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 635 Requirement Levels", BCP 14, RFC 2119, 636 DOI 10.17487/RFC2119, March 1997, 637 . 639 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 640 "Definition of the Differentiated Services Field (DS 641 Field) in the IPv4 and IPv6 Headers", RFC 2474, 642 DOI 10.17487/RFC2474, December 1998, 643 . 645 [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., 646 and W. Weiss, "An Architecture for Differentiated 647 Services", RFC 2475, DOI 10.17487/RFC2475, December 1998, 648 . 650 15.2. Informative References 652 [carlberg-lbe-2001] 653 Carlberg, K., Gevros, P., and J. Crowcroft, "Lower than 654 best effort: a design and implementation", SIGCOMM 655 Computer Communications Review Volume 31, Issue 2 656 supplement, April 2001, 657 . 659 [chown-lbe-2003] 660 Chown, T., Ferrari, T., Leinen, S., Sabatino, R., Simar, 661 N., and S. Venaas, "Less than Best Effort: Application 662 Scenarios and Experimental Results", In Proceedings of the 663 Second International Workshop on Quality of Service in 664 Multiservice IP Networks (QoS-IP 2003), Lecture Notes in 665 Computer Science, vol 2601. Springer, Berlin, 666 Heidelberg Pages 131-144, February 2003, 667 . 669 [draft-bless-diffserv-lbe-phb-00] 670 Bless, R. and K. Wehrle, "A Lower Than Best-Effort Per-Hop 671 Behavior", draft-bless-diffserv-lbe-phb-00 (work in 672 progress), September 1999, . 675 [I-D.ietf-tsvwg-iana-dscp-registry] 676 Fairhurst, G., "IANA Assignment of DSCP Pool 3 (xxxx01) 677 Values to require Publication of a Standards Track or Best 678 Current Practice RFC", draft-ietf-tsvwg-iana-dscp- 679 registry-08 (work in progress), June 2018. 681 [I-D.ietf-tsvwg-rtcweb-qos] 682 Jones, P., Dhesikan, S., Jennings, C., and D. Druta, "DSCP 683 Packet Markings for WebRTC QoS", draft-ietf-tsvwg-rtcweb- 684 qos-18 (work in progress), August 2016. 686 [ietf99-secchi] 687 Secchi, R., Venne, A., and A. Custura, "Measurements 688 concerning the DSCP for a LE PHB", Presentation held at 689 99th IETF Meeting, TSVWG, Prague , July 2017, 690 . 694 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 695 of Explicit Congestion Notification (ECN) to IP", 696 RFC 3168, DOI 10.17487/RFC3168, September 2001, 697 . 699 [RFC3439] Bush, R. and D. Meyer, "Some Internet Architectural 700 Guidelines and Philosophy", RFC 3439, 701 DOI 10.17487/RFC3439, December 2002, 702 . 704 [RFC3662] Bless, R., Nichols, K., and K. Wehrle, "A Lower Effort 705 Per-Domain Behavior (PDB) for Differentiated Services", 706 RFC 3662, DOI 10.17487/RFC3662, December 2003, 707 . 709 [RFC3754] Bless, R. and K. Wehrle, "IP Multicast in Differentiated 710 Services (DS) Networks", RFC 3754, DOI 10.17487/RFC3754, 711 April 2004, . 713 [RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration 714 Guidelines for DiffServ Service Classes", RFC 4594, 715 DOI 10.17487/RFC4594, August 2006, 716 . 718 [RFC5053] Luby, M., Shokrollahi, A., Watson, M., and T. Stockhammer, 719 "Raptor Forward Error Correction Scheme for Object 720 Delivery", RFC 5053, DOI 10.17487/RFC5053, October 2007, 721 . 723 [RFC6297] Welzl, M. and D. Ros, "A Survey of Lower-than-Best-Effort 724 Transport Protocols", RFC 6297, DOI 10.17487/RFC6297, June 725 2011, . 727 [RFC6817] Shalunov, S., Hazel, G., Iyengar, J., and M. Kuehlewind, 728 "Low Extra Delay Background Transport (LEDBAT)", RFC 6817, 729 DOI 10.17487/RFC6817, December 2012, 730 . 732 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 733 Morris, J., Hansen, M., and R. Smith, "Privacy 734 Considerations for Internet Protocols", RFC 6973, 735 DOI 10.17487/RFC6973, July 2013, 736 . 738 [RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage 739 Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, 740 March 2017, . 742 [RFC8100] Geib, R., Ed. and D. Black, "Diffserv-Interconnection 743 Classes and Practice", RFC 8100, DOI 10.17487/RFC8100, 744 March 2017, . 746 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 747 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 748 May 2017, . 750 [RFC8325] Szigeti, T., Henry, J., and F. Baker, "Mapping Diffserv to 751 IEEE 802.11", RFC 8325, DOI 10.17487/RFC8325, February 752 2018, . 754 Appendix A. History of the LE PHB 756 A first version of this PHB was suggested by Roland Bless and Klaus 757 Wehrle in September 1999 [draft-bless-diffserv-lbe-phb-00], named "A 758 Lower Than Best-Effort Per-Hop Behavior". After some discussion in 759 the DiffServ Working Group Brian Carpenter and Kathie Nichols 760 proposed a "bulk handling" per-domain behavior and believed a PHB was 761 not necessary. Eventually, "Lower Effort" was specified as per- 762 domain behavior and finally became [RFC3662]. More detailed 763 information about its history can be found in Section 10 of 764 [RFC3662]. 766 There are several other names in use for this type of PHB or 767 associated service classes. Well-known is the QBone Scavenger 768 Service (QBSS) that was proposed in March 2001 within the Internet2 769 QoS Working Group. Alternative names are "Lower-than-best-effort" 770 [carlberg-lbe-2001] or "Less-than-best-effort" [chown-lbe-2003]. 772 Appendix B. Acknowledgments 774 Since text is borrowed from earlier Internet-Drafts and RFCs the co- 775 authors of previous specifications are acknowledged here: Kathie 776 Nichols and Klaus Wehrle. David Black, Toerless Eckert, Gorry 777 Fairhurst, and Ruediger Geib provided helpful comments and (also 778 text) suggestions. 780 Appendix C. Change History 782 This section briefly lists changes between Internet-Draft versions 783 for convenience. 785 Changes in Version 06: 787 o added Multicast Considerations section with input from Toerless 788 Eckert 790 o incorporated suggestions by David Black with respect to better 791 reflect legacy CS1 handling 793 Changes in Version 05: 795 o added scavenger service class into abstract 797 o added some more history 798 o added reference for "Myth of Over-Provisioning" in RFC3439 and 799 references to presentations w.r.t. codepoint choices 801 o added text to update draft-ietf-tsvwg-rtcweb-qos 803 o revised text on congestion control in case of remarking to BE 805 o added reference to DSCP measurement talk @IETF99 807 o small typo fixes 809 Changes in Version 04: 811 o Several editorial changes according to review from Gorry Fairhurst 813 o Changed the section structure a bit (moved subsections 1.1 and 1.2 814 into own sections 3 and 7 respectively) 816 o updated section 2 on requirements language 818 o added updates to RFC 8325 820 o tried to be more explicit what changes are required to RFCs 4594 821 and 8325 823 Changes in Version 03: 825 o Changed recommended codepoint to 000001 827 o Added text to explain the reasons for the DSCP choice 829 o Removed LE-min,LE-strict discussion 831 o Added one more potential use case: reporting errors or telemetry 832 data from OSs 834 o Added privacy considerations to the security section (not worth an 835 own section I think) 837 o Changed IANA considerations section 839 Changes in Version 02: 841 o Applied many editorial suggestions from David Black 843 o Added Multicast traffic use case 844 o Clarified what is required for deployment in section 1.2 845 (Deployment Considerations) 847 o Added text about implementations using AQMs and ECN usage 849 o Updated IANA section according to David Black's suggestions 851 o Revised text in the security section 853 o Changed copyright Notice to pre5378Trust200902 855 Changes in Version 01: 857 o Now obsoletes RFC 3662. 859 o Tried to be more precise in section 1.1 (Applicability) according 860 to R. Geib's suggestions, so rephrased several paragraphs. Added 861 text about congestion control 863 o Change section 2 (PHB Description) according to R. Geib's 864 suggestions. 866 o Added RFC 2119 language to several sentences. 868 o Detailed the description of remarking implications and 869 recommendations in Section 8. 871 o Added Section 10 to explicitly list changes with respect to RFC 872 4594, because this document will update it. 874 Appendix D. Note to RFC Editor 876 This section lists actions for the RFC editor during final 877 formatting. 879 o Please replace the occurrences of RFCXXXX in Section 10 and 880 Section 11 with the assigned RFC number for this document. 882 o Delete Appendix C. 884 o Delete this section. 886 Author's Address 887 Roland Bless 888 Karlsruhe Institute of Technology (KIT) 889 Kaiserstr. 12 890 Karlsruhe 76131 891 Germany 893 Phone: +49 721 608 46413 894 Email: roland.bless@kit.edu