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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 603, but not defined == Missing Reference: 'LE-PHB' is mentioned on line 532, but not defined == Missing Reference: 'RFC7657' is mentioned on line 609, 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) February 15, 2019 5 Updates: 4594,8325 (if approved) 6 Intended status: Standards Track 7 Expires: August 19, 2019 9 A Lower Effort Per-Hop Behavior (LE PHB) 10 draft-ietf-tsvwg-le-phb-09 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 August 19, 2019. 47 Copyright Notice 49 Copyright (c) 2019 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 . . . . . . . . . . . . . . . . . . . . . . . 6 80 5. Traffic Conditioning Actions . . . . . . . . . . . . . . . . 6 81 6. Recommended DS Codepoint . . . . . . . . . . . . . . . . . . 7 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 . . . . . . . . . . . . . . . . . . . . . 14 89 14. Security Considerations . . . . . . . . . . . . . . . . . . . 14 90 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 91 15.1. Normative References . . . . . . . . . . . . . . . . . . 15 92 15.2. Informative References . . . . . . . . . . . . . . . . . 15 93 Appendix A. History of the LE PHB . . . . . . . . . . . . . . . 17 94 Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . 18 95 Appendix C. Change History . . . . . . . . . . . . . . . . . . . 18 96 Appendix D. Note to RFC Editor . . . . . . . . . . . . . . . . . 20 97 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 21 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 packets that ought to consume network resources 113 only when no other traffic is demanding them. In this point of view, 114 packets forwarded by the LE PHB scavenge otherwise unused resources 115 only, which led to the name "scavenger service" in early Internet2 116 deployments (see Appendix A). Other commonly used names for LE PHB 117 type services are "Lower-than-best-effort" or "Less-than-best- 118 effort". Alternatively, the effect of this type of traffic on all 119 other network traffic is strictly limited ("no harm" property). This 120 is distinct from "best-effort" (BE) traffic since the network makes 121 no commitment to deliver LE packets. In contrast, BE traffic 122 receives an implied "good faith" commitment of at least some 123 available network resources. This document proposes a Lower Effort 124 Differentiated Services per-hop behavior (LE PHB) for handling this 125 "optional" traffic in a differentiated services node. 127 2. Requirements Language 129 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 130 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 131 "OPTIONAL" in this document are to be interpreted as described in BCP 132 14 [RFC2119][RFC8174] when, and only when, they appear in all 133 capitals, as shown here. 135 3. Applicability 137 A Lower Effort PHB is applicable for many applications that otherwise 138 use best-effort delivery. More specifically, it is suitable for 139 traffic and services that can tolerate strongly varying throughput 140 for their data flows, especially periods of very low throughput or 141 even starvation (i.e., long interruptions due to significant or even 142 complete packet loss). Therefore, an application sending an LE 143 marked flow needs to be able to tolerate short or (even very) long 144 interruptions due to the presence of severe congestion conditions 145 during the transmission of the flow. Thus, there ought to be an 146 expectation that packets of the LE PHB could be excessively delayed 147 or dropped when any other traffic is present. It is application- 148 dependent when a lack of progress is considered being a failure 149 (e.g., if a transport connection fails due to timing out, the 150 application may try several times to re-establish the transport 151 connection in order to resume the application session before finally 152 giving up). The LE PHB is suitable for sending traffic of low 153 urgency across a Differentiated Services (DS) domain or DS region. 155 Just like best-effort traffic, LE traffic SHOULD be congestion 156 controlled (i.e., use a congestion controlled transport or implement 157 an appropriate congestion control method [RFC2914] [RFC8085]). Since 158 LE traffic could be starved completely for a longer period of time, 159 transport protocols or applications (and their related congestion 160 control mechanisms) SHOULD be able to detect and react to such a 161 starvation situation. An appropriate reaction would be to resume the 162 transfer instead of aborting it, i.e., an LE optimized transport 163 ought to use appropriate retry strategies (e.g., exponential backoff 164 with an upper bound) as well as corresponding retry and timeout 165 limits in order to avoid the loss of the connection due to the 166 mentioned starvation periods. While it is desirable to achieve a 167 quick resumption of the transfer as soon as resources become 168 available again, it may be difficult to achieve this in practice. In 169 lack of a transport protocol and congestion control that are adapted 170 to LE, applications can also use existing common transport protocols 171 and implement session resumption by trying to re-establish failed 172 connections. Congestion control is not only useful to let the flows 173 within the LE behavior aggregate adapt to the available bandwidth 174 that may be highly fluctuating, but is also essential if LE traffic 175 is mapped to the default PHB in DS domains that do not support LE. 176 In this case, use of background transport protocols, e.g., similar to 177 LEDBAT [RFC6817], is expedient. 179 Use of the LE PHB might assist a network operator in moving certain 180 kinds of traffic or users to off-peak times. Alternatively, or in 181 addition, packets can be designated for the LE PHB when the goal is 182 to protect all other packet traffic from competition with the LE 183 aggregate while not completely banning LE traffic from the network. 184 An LE PHB SHOULD NOT be used for a customer's "normal Internet" 185 traffic nor should packets be "downgraded" to the LE PHB instead of 186 being dropped, particularly when the packets are unauthorized 187 traffic. The LE PHB is expected to have applicability in networks 188 that have at least some unused capacity at certain periods. 190 The LE PHB allows networks to protect themselves from selected types 191 of traffic as a complement to giving preferential treatment to other 192 selected traffic aggregates. LE ought not to be used for the general 193 case of downgraded traffic, but could be used by design, e.g., to 194 protect an internal network from untrusted external traffic sources. 195 In this case there is no way for attackers to preempt internal (non 196 LE) traffic by flooding. Another use case in this regard is 197 forwarding of multicast traffic from untrusted sources. Multicast 198 forwarding is currently enabled within domains only for specific 199 sources within a domain, but not for sources from anywhere in the 200 Internet. A main problem is that multicast routing creates traffic 201 sources at (mostly) unpredictable branching points within a domain, 202 potentially leading to congestion and packet loss. In the case of 203 multicast traffic packets from untrusted sources are forwarded as LE 204 traffic, they will not harm traffic from non-LE behavior aggregates. 205 A further related use case is mentioned in [RFC3754]: preliminary 206 forwarding of non-admitted multicast traffic. 208 There is no intrinsic reason to limit the applicability of the LE PHB 209 to any particular application or type of traffic. It is intended as 210 an additional traffic engineering tool for network administrators. 211 For instance, it can be used to fill protection capacity of 212 transmission links that is otherwise unused. Some network providers 213 keep link utilization below 50% to ensure that all traffic is 214 forwarded without loss after rerouting caused by a link failure (cf. 215 Section 6 of [RFC3439]). LE marked traffic can utilize the normally 216 unused capacity and will be preempted automatically in case of link 217 failure when 100% of the link capacity is required for all other 218 traffic. Ideally, applications mark their packets as LE traffic, 219 since they know the urgency of flows. 221 Example uses for the LE PHB: 223 o For traffic caused by world-wide web search engines while they 224 gather information from web servers. 226 o For software updates or dissemination of new releases of operating 227 systems. 229 o For reporting errors or telemetry data from operating systems or 230 applications. 232 o For backup traffic or non-time critical synchronization or 233 mirroring traffic. 235 o For content distribution transfers between caches. 237 o For preloading or prefetching objects from web sites. 239 o For network news and other "bulk mail" of the Internet. 241 o For "downgraded" traffic from some other PHB when this does not 242 violate the operational objectives of the other PHB. 244 o For multicast traffic from untrusted (e.g., non-local) sources. 246 4. PHB Description 248 The LE PHB is defined in relation to the default PHB (best-effort). 249 A packet forwarded with the LE PHB SHOULD have lower precedence than 250 packets forwarded with the default PHB, i.e., in the case of 251 congestion, LE marked traffic SHOULD be dropped prior to dropping any 252 default PHB traffic. Ideally, LE packets would be forwarded only 253 when no packet with any other PHB is awaiting transmission. This 254 means that in case of link resource contention LE traffic can be 255 starved completely, which may not be always desired by the network 256 operator's policy. The used scheduler to implement the LE PHB may 257 reflect this policy accordingly. 259 A straightforward implementation could be a simple priority scheduler 260 serving the default PHB queue with higher priority than the lower- 261 effort PHB queue. Alternative implementations may use scheduling 262 algorithms that assign a very small weight to the LE class. This, 263 however, could sometimes cause better service for LE packets compared 264 to BE packets in cases when the BE share is fully utilized and the LE 265 share not. 267 If a dedicated LE queue is not available, an active queue management 268 mechanism within a common BE/LE queue could also be used. This could 269 drop all arriving LE packets as soon as certain queue length or 270 sojourn time thresholds are exceeded. 272 Since congestion control is also useful within the LE traffic class, 273 Explicit Congestion Notification (ECN) [RFC3168] SHOULD be used for 274 LE packets, too. More specifically, an LE implementation SHOULD also 275 apply CE marking for ECT marked packets and transport protocols used 276 for LE SHOULD support and employ ECN. 278 5. Traffic Conditioning Actions 280 If possible, packets SHOULD be pre-marked in DS-aware end systems by 281 applications due to their specific knowledge about the particular 282 precedence of packets. There is no incentive for DS domains to 283 distrust this initial marking, because letting LE traffic enter a DS 284 domain causes no harm. Thus, any policing such as limiting the rate 285 of LE traffic is not necessary at the DS boundary. 287 As for most other PHBs an initial classification and marking can be 288 also performed at the first DS boundary node according to the DS 289 domain's own policies (e.g., as protection measure against untrusted 290 sources). However, non-LE traffic (e.g., BE traffic) SHOULD NOT be 291 remarked to LE on a regular basis without consent or knowledge of the 292 user. See also remarks with respect to downgrading in Section 3 and 293 Section 8. 295 6. Recommended DS Codepoint 297 The RECOMMENDED codepoint for the LE PHB is '000001'. 299 Earlier specifications [RFC4594] recommended to use CS1 as codepoint 300 (as mentioned in [RFC3662]). This is problematic since it may cause 301 a priority inversion in Diffserv domains that treat CS1 as originally 302 proposed in [RFC2474], resulting in forwarding LE packets with higher 303 precedence than BE packets. Existing implementations SHOULD 304 transition to use the unambiguous LE codepoint '000001' whenever 305 possible. 307 This particular codepoint was chosen due to measurements on the 308 currently observable DSCP remarking behavior in the Internet 309 [ietf99-secchi]. Since some network domains set the former IP 310 precedence bits to zero, it is possible that some other standardized 311 DSCPs get mapped to the LE PHB DSCP if it were taken from the DSCP 312 standards action pool 1 (xxxxx0). 314 7. Deployment Considerations 316 In order to enable LE support, DS nodes typically only need 318 o A BA classifier (Behavior Aggregate classifier, see [RFC2475]) 319 that classifies packets according to the LE DSCP 321 o A dedicated LE queue 323 o A suitable scheduling discipline, e.g., simple priority queueing 325 Alternatively, implementations could use active queue management 326 mechanisms instead of a dedicated LE queue, e.g., dropping all 327 arriving LE packets when certain queue length or sojourn time 328 thresholds are exceeded. 330 Internet-wide deployment of the LE PHB is eased by the following 331 properties: 333 o No harm to other traffic: since the LE PHB has the lowest 334 forwarding priority it does not consume resources from other PHBs. 336 Deployment across different provider domains with LE support 337 causes no trust issues or attack vectors to existing (non LE) 338 traffic. Thus, providers can trust LE markings from end-systems, 339 i.e., there is no need to police or remark incoming LE traffic. 341 o No PHB parameters or configuration of traffic profiles: the LE PHB 342 itself possesses no parameters that need to be set or configured. 343 Similarly, since LE traffic requires no admission or policing, it 344 is not necessary to configure traffic profiles. 346 o No traffic conditioning mechanisms: the LE PHB requires no traffic 347 meters, droppers, or shapers. See also Section 5 for further 348 discussion. 350 Operators of DS domains that cannot or do not want to implement the 351 LE PHB (e.g., because there is no separate LE queue available in the 352 corresponding nodes) SHOULD NOT drop packets marked with the LE DSCP. 353 They SHOULD map packets with this DSCP to the default PHB and SHOULD 354 preserve the LE DSCP marking. DS domains operators that do not 355 implement the LE PHB should be aware that they violate the "no harm" 356 property of LE. See also Section 8 for further discussion of 357 forwarding LE traffic with the default PHB instead. 359 8. Remarking to other DSCPs/PHBs 361 "DSCP bleaching", i.e., setting the DSCP to '000000' (default PHB) is 362 NOT RECOMMENDED for this PHB. This may cause effects that are in 363 contrast to the original intent in protecting BE traffic from LE 364 traffic (no harm property). In the case that a DS domain does not 365 support the LE PHB, its nodes SHOULD treat LE marked packets with the 366 default PHB instead (by mapping the LE DSCP to the default PHB), but 367 they SHOULD do so without remarking to DSCP '000000'. The reason for 368 this is that later traversed DS domains may then have still the 369 possibility to treat such packets according to the LE PHB. 371 Operators of DS domains that forward LE traffic within the BE 372 aggregate need to be aware of the implications, i.e., induced 373 congestion situations and quality-of-service degradation of the 374 original BE traffic. In this case, the LE property of not harming 375 other traffic is no longer fulfilled. To limit the impact in such 376 cases, traffic policing of the LE aggregate MAY be used. 378 In case LE marked packets are effectively carried within the default 379 PHB (i.e., forwarded as best-effort traffic) they get a better 380 forwarding treatment than expected. For some applications and 381 services, it is favorable if the transmission is finished earlier 382 than expected. However, in some cases it may be against the original 383 intention of the LE PHB user to strictly send the traffic only if 384 otherwise unused resources are available. In case LE traffic is 385 mapped to the default PHB, LE traffic may compete with BE traffic for 386 the same resources and thus adversely affect the original BE 387 aggregate. Applications that want to ensure the lower precedence 388 compared to BE traffic even in such cases SHOULD use additionally a 389 corresponding Lower-than-Best-Effort transport protocol [RFC6297], 390 e.g., LEDBAT [RFC6817]. 392 A DS domain that still uses DSCP CS1 for marking LE traffic 393 (including Low Priority-Data as defined in [RFC4594] or the old 394 definition in [RFC3662]) SHOULD remark traffic to the LE DSCP 395 '000001' at the egress to the next DS domain. This increases the 396 probability that the DSCP is preserved end-to-end, whereas a CS1 397 marked packet may be remarked by the default DSCP if the next domain 398 is applying Diffserv-intercon [RFC8100]. 400 9. Multicast Considerations 402 Basically the multicast considerations in [RFC3754] apply. However, 403 using the Lower Effort PHB for multicast requires to pay special 404 attention to the way how packets get replicated inside routers. Due 405 to multicast packet replication, resource contention may actually 406 occur even before a packet is forwarded to its output port and in the 407 worst case, these forwarding resources are missing for higher 408 prioritized multicast or even unicast packets. 410 Several forwarding error correction coding schemes such as fountain 411 codes (e.g., [RFC5053]) allow reliable data delivery even in 412 environments with a potential high amount of packet loss in 413 transmission. When used for example over satellite links or other 414 broadcast media, this means that receivers that lose 80% of packets 415 in transmission simply need 5 times as long to receive the complete 416 data than those receivers experiencing no loss (without any receiver 417 feedback required). 419 Superficially viewed, it may sound very attractive to use IP 420 multicast with the LE PHB to build this type of opportunistic 421 reliable distribution in IP networks, but it can only be usefully 422 deployed with routers that do not experience forwarding/replication 423 resource starvation when a large amount of packets (virtually) need 424 to be replicated to links where the LE queue is full. 426 Thus, packet replication of LE marked packets should consider the 427 situation at the respective output links: it is a waste of internal 428 forwarding resources if a packet is replicated to output links that 429 have no resources left for LE forwarding. In those cases a packet 430 would have been replicated just to be dropped immediately after 431 finding a filled LE queue at the respective output port. Such 432 behavior could be avoided for example by using a conditional internal 433 packet replication: a packet would then only be replicated in case 434 the output link is not fully used. This conditional replication, 435 however, is probably not widely implemented. 437 While the resource contention problem caused by multicast packet 438 replication is also true for other Diffserv PHBs, LE forwarding is 439 special, because often it is assumed that LE packets get only 440 forwarded in case of available resources at the output ports. The 441 previously mentioned redundancy data traffic could nicely use the 442 varying available residual bandwidth being utilized the by LE PHB, 443 but only if the previously specific requirements in the internal 444 implementation of the network devices are considered. 446 10. The Update to RFC 4594 448 [RFC4594] recommended to use CS1 as codepoint in section 4.10, 449 whereas CS1 was defined in [RFC2474] to have a higher precedence than 450 CS0, i.e., the default PHB. Consequently, Diffserv domains 451 implementing CS1 according to [RFC2474] will cause a priority 452 inversion for LE packets that contradicts with the original purpose 453 of LE. Therefore, every occurrence of the CS1 DSCP is replaced by 454 the LE DSCP. 456 Changes: 458 o This update to RFC 4594 removes the following entry from figure 3: 460 |---------------+---------+-------------+--------------------------| 461 | Low-Priority | CS1 | 001000 | Any flow that has no BW | 462 | Data | | | assurance | 463 ------------------------------------------------------------------ 465 and replaces this by the following entry: 467 |---------------+---------+-------------+--------------------------| 468 | Low-Priority | LE | 000001 | Any flow that has no BW | 469 | Data | | | assurance | 470 ------------------------------------------------------------------ 472 o This update to RFC 4594 extends the Notes text below figure 3 that 473 currently states "Notes for Figure 3: Default Forwarding (DF) and 474 Class Selector 0 (CS0) provide equivalent behavior and use the 475 same DS codepoint, '000000'." to state "Notes for Figure 3: 476 Default Forwarding (DF) and Class Selector 0 (CS0) provide 477 equivalent behavior and use the same DS codepoint, '000000'. The 478 prior recommendation to use the CS1 DSCP for Low-Priority Data has 479 been replaced by the current recommendation to use the LE DSCP, 480 '000001'." 482 o This update to RFC 4594 removes the following entry from figure 4: 484 |---------------+------+-------------------+---------+--------+----| 485 | Low-Priority | CS1 | Not applicable | RFC3662 | Rate | Yes| 486 | Data | | | | | | 487 ------------------------------------------------------------------ 489 and replaces this by the following entry: 491 |---------------+------+-------------------+---------+--------+----| 492 | Low-Priority | LE | Not applicable | RFCXXXX | Rate | Yes| 493 | Data | | | | | | 494 ------------------------------------------------------------------ 496 o Section 2.3 of [RFC4594] specifies: "In network segments that use 497 IP precedence marking, only one of the two service classes can be 498 supported, High-Throughput Data or Low-Priority Data. We 499 RECOMMEND that the DSCP value(s) of the unsupported service class 500 be changed to 000xx1 on ingress and changed back to original 501 value(s) on egress of the network segment that uses precedence 502 marking. For example, if Low-Priority Data is mapped to Standard 503 service class, then 000001 DSCP marking MAY be used to distinguish 504 it from Standard marked packets on egress." This document removes 505 this recommendation, because by using the herein defined LE DSCP 506 such remarking is not necessary. So even if Low-Priority Data is 507 unsupported (i.e., mapped to the default PHB) the LE DSCP should 508 be kept across the domain as RECOMMENDED in Section 8. That 509 removed text is replaced by: "In network segments that use IP 510 Precedence marking, the Low-Priority Data service class receives 511 the same Diffserv QoS as the Standard service class when the LE 512 DSCP is used for Low-Priority Data traffic. This is acceptable 513 behavior for the Low-Priority Data service class, although it is 514 not the preferred behavior." 516 o This document removes the following line of RFC 4594, 517 Section 4.10: "The RECOMMENDED DSCP marking is CS1 (Class Selector 518 1)." and replaces this with the following text: "The RECOMMENDED 519 DSCP marking is LE (Lower Effort), which replaces the prior 520 recommendation for CS1 (Class Selector 1) marking." 522 11. The Update to RFC 8325 524 Section 4.2.10 of RFC 8325 [RFC8325] specifies "[RFC3662] and 525 [RFC4594] both recommend Low-Priority Data be marked CS1 DSCP." 526 which is updated to "[RFC3662] recommends that Low-Priority Data be 527 marked CS1 DSCP. [RFC4594] as updated by [RFCXXXX] recommends Low- 528 Priority Data be marked LE DSCP." 530 This document removes the following paragraph of RFC 8325, 531 Section 4.2.10 because this document makes the anticipated change: 532 "Note: This marking recommendation may change in the future, as [LE- 533 PHB] defines a Lower Effort (LE) PHB for Low-Priority Data traffic 534 and recommends an additional DSCP for this traffic." 536 Section 4.2.10 of RFC 8325 [RFC8325] specifies "therefore, it is 537 RECOMMENDED to map Low-Priority Data traffic marked CS1 DSCP to UP 1" 538 which is updated to "therefore, it is RECOMMENDED to map Low-Priority 539 Data traffic marked with LE DSCP or legacy CS1 DSCP to UP 1" 541 This update to RFC 8325 replaces the following entry from figure 1: 543 +---------------+------+----------+-------------+--------------------+ 544 | Low-Priority | CS1 | RFC 3662 | 1 | AC_BK (Background) | 545 | Data | | | | | 546 +--------------------------------------------------------------------+ 548 by the following entries: 550 +---------------+------+----------+-------------+--------------------+ 551 | Low-Priority | LE | RFCXXXX | 1 | AC_BK (Background) | 552 | Data | | | | | 553 +--------------------------------------------------------------------+ 554 | Low-Priority | CS1 | RFC 3662 | 1 | AC_BK (Background) | 555 | Data (legacy) | | | | | 556 +--------------------------------------------------------------------+ 558 12. The Update to draft-ietf-tsvwg-rtcweb-qos 560 Section 5 of [I-D.ietf-tsvwg-rtcweb-qos] describes the Recommended 561 DSCP Values for WebRTC Applications 563 This update to [I-D.ietf-tsvwg-rtcweb-qos] replaces all occurrences 564 of CS1 with LE in Table 1: 566 +------------------------+-------+------+-------------+-------------+ 567 | Flow Type | Very | Low | Medium | High | 568 | | Low | | | | 569 +------------------------+-------+------+-------------+-------------+ 570 | Audio | LE | DF | EF (46) | EF (46) | 571 | | (1) | (0) | | | 572 | | | | | | 573 | Interactive Video with | LE | DF | AF42, AF43 | AF41, AF42 | 574 | or without Audio | (1) | (0) | (36, 38) | (34, 36) | 575 | | | | | | 576 | Non-Interactive Video | LE | DF | AF32, AF33 | AF31, AF32 | 577 | with or without Audio | (1) | (0) | (28, 30) | (26, 28) | 578 | | | | | | 579 | Data | LE | DF | AF11 | AF21 | 580 | | (1) | (0) | | | 581 +------------------------+-------+------+-------------+-------------+ 583 and updates the following paragraph: 585 "The above table assumes that packets marked with CS1 are treated as 586 "less than best effort", such as the LE behavior described in 587 [RFC3662]. However, the treatment of CS1 is implementation 588 dependent. If an implementation treats CS1 as other than "less than 589 best effort", then the actual priority (or, more precisely, the per- 590 hop-behavior) of the packets may be changed from what is intended. 591 It is common for CS1 to be treated the same as DF, so applications 592 and browsers using CS1 cannot assume that CS1 will be treated 593 differently than DF [RFC7657]. However, it is also possible per 594 [RFC2474] for CS1 traffic to be given better treatment than DF, thus 595 caution should be exercised when electing to use CS1. This is one of 596 the cases where marking packets using these recommendations can make 597 things worse." 599 as follows: 601 "The above table assumes that packets marked with LE are treated as 602 lower effort (i.e., "less than best effort"), such as the LE behavior 603 described in [RFCXXXX]. However, the treatment of LE is 604 implementation dependent. If an implementation treats LE as other 605 than "less than best effort", then the actual priority (or, more 606 precisely, the per- hop-behavior) of the packets may be changed from 607 what is intended. It is common for LE to be treated the same as DF, 608 so applications and browsers using LE cannot assume that LE will be 609 treated differently than DF [RFC7657]. During development of this 610 document, the CS1 DSCP was recommended for "very low" application 611 priority traffic; implementations that followed that recommendation 612 SHOULD be updated to use the LE DSCP instead of the CS1 DSCP." 614 13. IANA Considerations 616 This document assigns the Differentiated Services Field Codepoint 617 (DSCP) '000001' from the Differentiated Services Field Codepoints 618 (DSCP) registry (https://www.iana.org/assignments/dscp-registry/dscp- 619 registry.xhtml) (Pool 3, Codepoint Space xxxx01, Standards Action) to 620 the LE PHB. This document suggests to use a DSCP from Pool 3 in 621 order to avoid problems for other PHB marked flows to become 622 accidentally remarked as LE PHB, e.g., due to partial DSCP bleaching. 623 See [RFC8436] for re-classifying Pool 3 for Standards Action. 625 IANA is requested to update the registry as follows: 627 o Name: LE 629 o Value (Binary): 000001 631 o Value (Decimal): 1 633 o Reference: [RFC number of this memo] 635 14. Security Considerations 637 There are no specific security exposures for this PHB. Since it 638 defines a new class of low forwarding priority, remarking other 639 traffic as LE traffic may lead to quality-of-service degradation of 640 such traffic. Thus, any attacker that is able to modify the DSCP of 641 a packet to LE may carry out a downgrade attack. See the general 642 security considerations in [RFC2474] and [RFC2475]. 644 With respect to privacy, an attacker could use the information from 645 the DSCP to infer that the transferred (probably even encrypted) 646 content is considered of low priority or low urgency by a user, in 647 case the DSCP was set on the user's request. On the one hand, this 648 disclosed information is useful only if correlation with metadata 649 (such as the user's IP address) and/or other flows reveal user 650 identity. On the other hand, it might help an observer (e.g., a 651 state level actor) who is interested in learning about the user's 652 behavior from observed traffic: LE marked background traffic (such as 653 software downloads, operating system updates, or telemetry data) may 654 be less interesting for surveillance than general web traffic. 655 Therefore, the LE marking may help the observer to focus on 656 potentially more interesting traffic (however, the user may exploit 657 this particular assumption and deliberately hide interesting traffic 658 in the LE aggregate). Apart from such considerations, the impact of 659 disclosed information by the LE DSCP is likely negligible in most 660 cases given the numerous traffic analysis possibilities and general 661 privacy threats (e.g., see [RFC6973]). 663 15. References 665 15.1. Normative References 667 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 668 Requirement Levels", BCP 14, RFC 2119, 669 DOI 10.17487/RFC2119, March 1997, 670 . 672 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 673 "Definition of the Differentiated Services Field (DS 674 Field) in the IPv4 and IPv6 Headers", RFC 2474, 675 DOI 10.17487/RFC2474, December 1998, 676 . 678 [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., 679 and W. Weiss, "An Architecture for Differentiated 680 Services", RFC 2475, DOI 10.17487/RFC2475, December 1998, 681 . 683 15.2. Informative References 685 [carlberg-lbe-2001] 686 Carlberg, K., Gevros, P., and J. Crowcroft, "Lower than 687 best effort: a design and implementation", SIGCOMM 688 Computer Communications Review Volume 31, Issue 2 689 supplement, April 2001, 690 . 692 [chown-lbe-2003] 693 Chown, T., Ferrari, T., Leinen, S., Sabatino, R., Simar, 694 N., and S. Venaas, "Less than Best Effort: Application 695 Scenarios and Experimental Results", In Proceedings of the 696 Second International Workshop on Quality of Service in 697 Multiservice IP Networks (QoS-IP 2003), Lecture Notes in 698 Computer Science, vol 2601. Springer, Berlin, 699 Heidelberg Pages 131-144, February 2003, 700 . 702 [draft-bless-diffserv-lbe-phb-00] 703 Bless, R. and K. Wehrle, "A Lower Than Best-Effort Per-Hop 704 Behavior", draft-bless-diffserv-lbe-phb-00 (work in 705 progress), September 1999, . 708 [I-D.ietf-tsvwg-rtcweb-qos] 709 Jones, P., Dhesikan, S., Jennings, C., and D. Druta, "DSCP 710 Packet Markings for WebRTC QoS", draft-ietf-tsvwg-rtcweb- 711 qos-18 (work in progress), August 2016. 713 [ietf99-secchi] 714 Secchi, R., Venne, A., and A. Custura, "Measurements 715 concerning the DSCP for a LE PHB", Presentation held at 716 99th IETF Meeting, TSVWG, Prague , July 2017, 717 . 721 [RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, 722 RFC 2914, DOI 10.17487/RFC2914, September 2000, 723 . 725 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 726 of Explicit Congestion Notification (ECN) to IP", 727 RFC 3168, DOI 10.17487/RFC3168, September 2001, 728 . 730 [RFC3439] Bush, R. and D. Meyer, "Some Internet Architectural 731 Guidelines and Philosophy", RFC 3439, 732 DOI 10.17487/RFC3439, December 2002, 733 . 735 [RFC3662] Bless, R., Nichols, K., and K. Wehrle, "A Lower Effort 736 Per-Domain Behavior (PDB) for Differentiated Services", 737 RFC 3662, DOI 10.17487/RFC3662, December 2003, 738 . 740 [RFC3754] Bless, R. and K. Wehrle, "IP Multicast in Differentiated 741 Services (DS) Networks", RFC 3754, DOI 10.17487/RFC3754, 742 April 2004, . 744 [RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration 745 Guidelines for DiffServ Service Classes", RFC 4594, 746 DOI 10.17487/RFC4594, August 2006, 747 . 749 [RFC5053] Luby, M., Shokrollahi, A., Watson, M., and T. Stockhammer, 750 "Raptor Forward Error Correction Scheme for Object 751 Delivery", RFC 5053, DOI 10.17487/RFC5053, October 2007, 752 . 754 [RFC6297] Welzl, M. and D. Ros, "A Survey of Lower-than-Best-Effort 755 Transport Protocols", RFC 6297, DOI 10.17487/RFC6297, June 756 2011, . 758 [RFC6817] Shalunov, S., Hazel, G., Iyengar, J., and M. Kuehlewind, 759 "Low Extra Delay Background Transport (LEDBAT)", RFC 6817, 760 DOI 10.17487/RFC6817, December 2012, 761 . 763 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 764 Morris, J., Hansen, M., and R. Smith, "Privacy 765 Considerations for Internet Protocols", RFC 6973, 766 DOI 10.17487/RFC6973, July 2013, 767 . 769 [RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage 770 Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, 771 March 2017, . 773 [RFC8100] Geib, R., Ed. and D. Black, "Diffserv-Interconnection 774 Classes and Practice", RFC 8100, DOI 10.17487/RFC8100, 775 March 2017, . 777 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 778 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 779 May 2017, . 781 [RFC8325] Szigeti, T., Henry, J., and F. Baker, "Mapping Diffserv to 782 IEEE 802.11", RFC 8325, DOI 10.17487/RFC8325, February 783 2018, . 785 [RFC8436] Fairhurst, G., "Update to IANA Registration Procedures for 786 Pool 3 Values in the Differentiated Services Field 787 Codepoints (DSCP) Registry", RFC 8436, 788 DOI 10.17487/RFC8436, August 2018, 789 . 791 Appendix A. History of the LE PHB 793 A first version of this PHB was suggested by Roland Bless and Klaus 794 Wehrle in September 1999 [draft-bless-diffserv-lbe-phb-00], named "A 795 Lower Than Best-Effort Per-Hop Behavior". After some discussion in 796 the Diffserv Working Group Brian Carpenter and Kathie Nichols 797 proposed a "bulk handling" per-domain behavior and believed a PHB was 798 not necessary. Eventually, "Lower Effort" was specified as per- 799 domain behavior and finally became [RFC3662]. More detailed 800 information about its history can be found in Section 10 of 801 [RFC3662]. 803 There are several other names in use for this type of PHB or 804 associated service classes. Well-known is the QBone Scavenger 805 Service (QBSS) that was proposed in March 2001 within the Internet2 806 QoS Working Group. Alternative names are "Lower-than-best-effort" 807 [carlberg-lbe-2001] or "Less-than-best-effort" [chown-lbe-2003]. 809 Appendix B. Acknowledgments 811 Since text is partially borrowed from earlier Internet-Drafts and 812 RFCs the co-authors of previous specifications are acknowledged here: 813 Kathie Nichols and Klaus Wehrle. David Black, Olivier Bonaventure, 814 Spencer Dawkins, Toerless Eckert, Gorry Fairhurst, Ruediger Geib, and 815 Kyle Rose provided helpful comments and (partially also text) 816 suggestions. 818 Appendix C. Change History 820 This section briefly lists changes between Internet-Draft versions 821 for convenience. 823 Changes in Version 09: 825 o Incorporated comments from IETF Last Call: 827 * from Olivier Bonaventure: added a bit of text for session 828 resumption and congestion control aspects as well as ECN usage. 830 * from Kyle Rose: Revised privacy considerations text in Security 831 Considerations Section 833 Changes in Version 08: 835 o revised two sentences as suggested by Spencer Dawkins 837 Changes in Version 07: 839 o revised some text for clarification according to comments from 840 Spencer Dawkins 842 Changes in Version 06: 844 o added Multicast Considerations section with input from Toerless 845 Eckert 847 o incorporated suggestions by David Black with respect to better 848 reflect legacy CS1 handling 850 Changes in Version 05: 852 o added scavenger service class into abstract 854 o added some more history 856 o added reference for "Myth of Over-Provisioning" in RFC3439 and 857 references to presentations w.r.t. codepoint choices 859 o added text to update draft-ietf-tsvwg-rtcweb-qos 861 o revised text on congestion control in case of remarking to BE 863 o added reference to DSCP measurement talk @IETF99 865 o small typo fixes 867 Changes in Version 04: 869 o Several editorial changes according to review from Gorry Fairhurst 871 o Changed the section structure a bit (moved subsections 1.1 and 1.2 872 into own sections 3 and 7 respectively) 874 o updated section 2 on requirements language 876 o added updates to RFC 8325 878 o tried to be more explicit what changes are required to RFCs 4594 879 and 8325 881 Changes in Version 03: 883 o Changed recommended codepoint to 000001 885 o Added text to explain the reasons for the DSCP choice 887 o Removed LE-min,LE-strict discussion 889 o Added one more potential use case: reporting errors or telemetry 890 data from OSs 892 o Added privacy considerations to the security section (not worth an 893 own section I think) 895 o Changed IANA considerations section 897 Changes in Version 02: 899 o Applied many editorial suggestions from David Black 900 o Added Multicast traffic use case 902 o Clarified what is required for deployment in section 1.2 903 (Deployment Considerations) 905 o Added text about implementations using AQMs and ECN usage 907 o Updated IANA section according to David Black's suggestions 909 o Revised text in the security section 911 o Changed copyright Notice to pre5378Trust200902 913 Changes in Version 01: 915 o Now obsoletes RFC 3662. 917 o Tried to be more precise in section 1.1 (Applicability) according 918 to R. Geib's suggestions, so rephrased several paragraphs. Added 919 text about congestion control 921 o Change section 2 (PHB Description) according to R. Geib's 922 suggestions. 924 o Added RFC 2119 language to several sentences. 926 o Detailed the description of remarking implications and 927 recommendations in Section 8. 929 o Added Section 10 to explicitly list changes with respect to RFC 930 4594, because this document will update it. 932 Appendix D. Note to RFC Editor 934 This section lists actions for the RFC editor during final 935 formatting. 937 o Please replace the occurrences of RFCXXXX in Section 10 and 938 Section 11 with the assigned RFC number for this document. 940 o Delete Appendix C. 942 o Delete this section. 944 Author's Address 946 Roland Bless 947 Karlsruhe Institute of Technology (KIT) 948 Kaiserstr. 12 949 Karlsruhe 76131 950 Germany 952 Phone: +49 721 608 46413 953 Email: roland.bless@kit.edu