idnits 2.17.1 draft-ietf-tsvwg-le-phb-07.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- -- The draft header indicates that this document updates RFC8325, but the abstract doesn't seem to directly say this. It does mention RFC8325 though, so this could be OK. -- The draft header indicates that this document updates RFC4594, but the abstract doesn't seem to directly say this. It does mention RFC4594 though, so this could be OK. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year (Using the creation date from RFC4594, updated by this document, for RFC5378 checks: 2005-02-14) -- The document seems to contain a disclaimer for pre-RFC5378 work, and may have content which was first submitted before 10 November 2008. The disclaimer is necessary when there are original authors that you have been unable to contact, or if some do not wish to grant the BCP78 rights to the IETF Trust. If you are able to get all authors (current and original) to grant those rights, you can and should remove the disclaimer; otherwise, the disclaimer is needed and you can ignore this comment. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (January 20, 2019) is 1916 days in the past. Is this intentional? 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 590, but not defined == Missing Reference: 'LE-PHB' is mentioned on line 520, but not defined == Missing Reference: 'RFC7657' is mentioned on line 596, 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) January 20, 2019 5 Updates: 4594,8325 (if approved) 6 Intended status: Standards Track 7 Expires: July 24, 2019 9 A Lower Effort Per-Hop Behavior (LE PHB) 10 draft-ietf-tsvwg-le-phb-07 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 July 24, 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 . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . . . . . 20 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 otherwise. In this 114 point of view, packets forwarded by the LE PHB scavenge otherwise 115 unused resources only, which led to the name "scavenger service" in 116 early Internet2 deployments (see Appendix A). Other commonly used 117 names for LE PHB type services are "Lower-than-best-effort" or "Less- 118 than-best-effort". Alternatively, the effect of this type of traffic 119 on all other network traffic is strictly limited ("no harm" 120 property). This is distinct from "best-effort" (BE) traffic since 121 the network makes no commitment to deliver LE packets. In contrast, 122 BE traffic receives an implied "good faith" commitment of at least 123 some available network resources. This document proposes a Lower 124 Effort Differentiated Services per-hop behavior (LE PHB) for handling 125 this "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. The LE PHB is suitable 148 for sending traffic of low urgency across a Differentiated Services 149 (DS) domain or DS region. 151 Just like best-effort traffic, LE traffic SHOULD be congestion 152 controlled (i.e., use a congestion controlled transport or implement 153 an appropriate congestion control method [RFC2914] [RFC8085]). Since 154 LE traffic could be starved completely for a longer period of time, 155 transport protocols or applications (and their related congestion 156 control mechanisms) SHOULD be able to detect and react to such a 157 starvation situation. An appropriate reaction would be to resume the 158 transfer instead of aborting it, i.e., an LE optimized transport 159 ought to use appropriate retry and timeout limits in order to avoid 160 the loss of the connection due to the mentioned starvation periods. 161 While it is desirable to achieve a quick resumption of the transfer 162 as soon as resources become available again, it may be difficult to 163 achieve this in practice. Congestion control is not only useful to 164 let the flows within the LE behavior aggregate adapt to the available 165 bandwidth that may be highly fluctuating, but is also essential if LE 166 traffic is mapped to the default PHB in DS domains that do not 167 support LE. In this case, use of background transport protocols, 168 e.g., similar to LEDBAT [RFC6817], is expedient. 170 Use of the LE PHB might assist a network operator in moving certain 171 kinds of traffic or users to off-peak times. Alternatively, or in 172 addition, packets can be designated for the LE PHB when the goal is 173 to protect all other packet traffic from competition with the LE 174 aggregate while not completely banning LE traffic from the network. 175 An LE PHB SHOULD NOT be used for a customer's "normal Internet" 176 traffic nor should packets be "downgraded" to the LE PHB instead of 177 being dropped, particularly when the packets are unauthorized 178 traffic. The LE PHB is expected to have applicability in networks 179 that have at least some unused capacity at certain periods. 181 The LE PHB allows networks to protect themselves from selected types 182 of traffic as a complement to giving preferential treatment to other 183 selected traffic aggregates. LE ought not to be used for the general 184 case of downgraded traffic, but could be used by design, e.g., to 185 protect an internal network from untrusted external traffic sources. 186 In this case there is no way for attackers to preempt internal (non 187 LE) traffic by flooding. Another use case in this regard is 188 forwarding of multicast traffic from untrusted sources. Multicast 189 forwarding is currently enabled within domains only for specific 190 sources within a domain, but not for sources from anywhere in the 191 Internet. A main problem is that multicast routing creates traffic 192 sources at (mostly) unpredictable branching points within a domain, 193 potentially leading to congestion and packet loss. In the case of 194 multicast traffic packets from untrusted sources are forwarded as LE 195 traffic, they will not harm traffic from non-LE behavior aggregates. 196 A further related use case is mentioned in [RFC3754]: preliminary 197 forwarding of non-admitted multicast traffic. 199 There is no intrinsic reason to limit the applicability of the LE PHB 200 to any particular application or type of traffic. It is intended as 201 an additional traffic engineering tool for network administrators. 202 For instance, it can be used to fill protection capacity of 203 transmission links that is otherwise unused. Some network providers 204 keep link utilization below 50% to ensure that all traffic is 205 forwarded without loss after rerouting caused by a link failure (cf. 206 Section 6 of [RFC3439]). LE marked traffic can utilize the normally 207 unused capacity and will be preempted automatically in case of link 208 failure when 100% of the link capacity is required for all other 209 traffic. Ideally, applications mark their packets as LE traffic, 210 since they know the urgency of flows. 212 Example uses for the LE PHB: 214 o For traffic caused by world-wide web search engines while they 215 gather information from web servers. 217 o For software updates or dissemination of new releases of operating 218 systems. 220 o For reporting errors or telemetry data from operating systems or 221 applications. 223 o For backup traffic or non-time critical synchronization or 224 mirroring traffic. 226 o For content distribution transfers between caches. 228 o For preloading or prefetching objects from web sites. 230 o For network news and other "bulk mail" of the Internet. 232 o For "downgraded" traffic from some other PHB when this does not 233 violate the operational objectives of the other PHB. 235 o For multicast traffic from untrusted (e.g., non-local) sources. 237 4. PHB Description 239 The LE PHB is defined in relation to the default PHB (best-effort). 240 A packet forwarded with the LE PHB SHOULD have lower precedence than 241 packets forwarded with the default PHB, i.e., in the case of 242 congestion, LE marked traffic SHOULD be dropped prior to dropping any 243 default PHB traffic. Ideally, LE packets SHOULD be forwarded only if 244 no packet with any other PHB is awaiting transmission. This means 245 that in case of link resource contention LE traffic can be starved 246 completely, which may not be always desired by the network operator's 247 policy. The used scheduler to implement the LE PHB may reflect this 248 policy accordingly. 250 A straightforward implementation could be a simple priority scheduler 251 serving the default PHB queue with higher priority than the lower- 252 effort PHB queue. Alternative implementations may use scheduling 253 algorithms that assign a very small weight to the LE class. This, 254 however, could sometimes cause better service for LE packets compared 255 to BE packets in cases when the BE share is fully utilized and the LE 256 share not. 258 If a dedicated LE queue is not available, an active queue management 259 mechanism within a common BE/LE queue could also be used. This could 260 drop all arriving LE packets as soon as certain queue length or 261 sojourn time thresholds are exceeded. 263 Since congestion control is also useful within the LE traffic class, 264 Explicit Congestion Notification [RFC3168] SHOULD be used for LE 265 packets, too. 267 5. Traffic Conditioning Actions 269 If possible, packets SHOULD be pre-marked in DS-aware end systems by 270 applications due to their specific knowledge about the particular 271 precedence of packets. There is no incentive for DS domains to 272 distrust this initial marking, because letting LE traffic enter a DS 273 domain causes no harm. Thus, any policing such as limiting the rate 274 of LE traffic is not necessary at the DS boundary. 276 As for most other PHBs an initial classification and marking can be 277 also performed at the first DS boundary node according to the DS 278 domain's own policies (e.g., as protection measure against untrusted 279 sources). However, non-LE traffic (e.g., BE traffic) SHOULD NOT be 280 remarked to LE on a regular basis without consent or knowledge of the 281 user. See also remarks with respect to downgrading in Section 3 and 282 Section 8. 284 6. Recommended DS Codepoint 286 The RECOMMENDED codepoint for the LE PHB is '000001'. 288 Earlier specifications [RFC4594] recommended to use CS1 as codepoint 289 (as mentioned in [RFC3662]). This is problematic since it may cause 290 a priority inversion in Diffserv domains that treat CS1 as originally 291 proposed in [RFC2474], resulting in forwarding LE packets with higher 292 precedence than BE packets. Existing implementations SHOULD 293 transition to use the unambiguous LE codepoint '000001' whenever 294 possible. 296 This particular codepoint was chosen due to measurements on the 297 currently observable DSCP remarking behavior in the Internet 298 [ietf99-secchi]. Since some network domains set the former IP 299 precedence bits to zero, it is possible that some other standardized 300 DSCPs get mapped to the LE PHB DSCP if it were taken from the DSCP 301 standards action pool 1 (xxxxx0). 303 7. Deployment Considerations 305 In order to enable LE support, DS nodes typically only need 307 o A BA classifier (Behavior Aggregate classifier, see [RFC2475]) 308 that classifies packets according to the LE DSCP 310 o A dedicated LE queue 312 o A suitable scheduling discipline, e.g., simple priority queueing 314 Alternatively, implementations could use active queue management 315 mechanisms instead of a dedicated LE queue, e.g., dropping all 316 arriving LE packets when certain queue length or sojourn time 317 thresholds are exceeded. 319 Internet-wide deployment of the LE PHB is eased by the following 320 properties: 322 o No harm to other traffic: since the LE PHB has the lowest 323 forwarding priority it does not consume resources from other PHBs. 324 Deployment across different provider domains with LE support 325 causes no trust issues or attack vectors to existing (non LE) 326 traffic. Thus, providers can trust LE markings from end-systems, 327 i.e., there is no need to police or remark incoming LE traffic. 329 o No PHB parameters or configuration of traffic profiles: the LE PHB 330 itself possesses no parameters that need to be set or configured. 332 Similarly, since LE traffic requires no admission or policing, it 333 is not necessary to configure traffic profiles. 335 o No traffic conditioning mechanisms: the LE PHB requires no traffic 336 meters, droppers, or shapers. See also Section 5 for further 337 discussion. 339 Operators of DS domains that cannot or do not want to implement the 340 LE PHB (e.g., because there is no separate LE queue available in the 341 corresponding nodes) SHOULD NOT drop packets marked with the LE DSCP. 342 They SHOULD map packets with this DSCP to the default PHB and SHOULD 343 preserve the LE DSCP marking. DS domains operators that do not 344 implement the LE PHB should be aware that they violate the "no harm" 345 property of LE. See also Section 8 for further discussion of 346 forwarding LE traffic with the default PHB instead. 348 8. Remarking to other DSCPs/PHBs 350 "DSCP bleaching", i.e., setting the DSCP to '000000' (default PHB) is 351 NOT RECOMMENDED for this PHB. This may cause effects that are in 352 contrast to the original intent in protecting BE traffic from LE 353 traffic (no harm property). In the case that a DS domain does not 354 support the LE PHB, its nodes SHOULD treat LE marked packets with the 355 default PHB instead (by mapping the LE DSCP to the default PHB), but 356 they SHOULD do so without remarking to DSCP '000000'. The reason for 357 this is that later traversed DS domains may then have still the 358 possibility to treat such packets according to the LE PHB. 360 Operators of DS domains that forward LE traffic within the BE 361 aggregate need to be aware of the implications, i.e., induced 362 congestion situations and quality-of-service degradation of the 363 original BE traffic. In this case, the LE property of not harming 364 other traffic is no longer fulfilled. To limit the impact in such 365 cases, traffic policing of the LE aggregate MAY be used. 367 In case LE marked packets are effectively carried within the default 368 PHB (i.e., forwarded as best-effort traffic) they get a better 369 forwarding treatment than expected. For some applications and 370 services, it is favorable if the transmission is finished earlier 371 than expected. However, in some cases it may be against the original 372 intention of the LE PHB user to strictly send the traffic only if 373 otherwise unused resources are available. In case LE traffic is 374 mapped to the default PHB, LE traffic may compete with BE traffic for 375 the same resources and thus adversely affect the original BE 376 aggregate. Applications that want to ensure the lower precedence 377 compared to BE traffic even in such cases SHOULD use additionally a 378 corresponding Lower-than-Best-Effort transport protocol [RFC6297], 379 e.g., LEDBAT [RFC6817]. 381 A DS domain that still uses DSCP CS1 for marking LE traffic 382 (including Low Priority-Data as defined in [RFC4594] or the old 383 definition in [RFC3662]) SHOULD remark traffic to the LE DSCP 384 '000001' at the egress to the next DS domain. This increases the 385 probability that the DSCP is preserved end-to-end, whereas a CS1 386 marked packet may be remarked by the default DSCP if the next domain 387 is applying Diffserv-intercon [RFC8100]. 389 9. Multicast Considerations 391 Basically the multicast considerations in [RFC3754] apply. However, 392 using the Lower Effort PHB for multicast requires to pay special 393 attention to the way how packets get replicated inside routers. Due 394 to multicast packet replication, resource contention may actually 395 occur even before a packet is forwarded to its output port and in the 396 worst case, these forwarding resources are missing for higher 397 prioritized multicast or even unicast packets. 399 Several forwarding error correction coding schemes such as fountain 400 codes (e.g., [RFC5053]) allow reliable data delivery even in 401 environments with a potential high amount of packet loss in 402 transmission. When used for example over satellite links or other 403 broadcast media, this means that receivers that lose 80% of packets 404 in transmission simply need 5 times as long to receive the complete 405 data than those receivers experiencing no loss (without any receiver 406 feedback required). 408 Superficially viewed, it may sound very attractive to use IP 409 multicast with the LE PHB to build this type of opportunistic 410 reliable distribution in IP networks, but it can only be usefully 411 deployed with routers that do not experience forwarding/replication 412 resource starvation when a large amount of packets (virtually) need 413 to be replicated to links where the LE queue is full. 415 Thus, packet replication of LE marked packets should consider the 416 situation at the respective output links: it is a waste of internal 417 forwarding resources if a packet is replicated to output links that 418 have no resources left for LE forwarding. In those cases a packet 419 would have been replicated just to be dropped immediately after 420 finding a filled LE queue at the respective output port. Such 421 behavior could be avoided for example by using a conditional internal 422 packet replication: a packet would then only be replicated in case 423 the output link is not fully used. This conditional replication, 424 however, is probably not widely implemented. 426 While the resource contention problem caused by multicast packet 427 replication is also true for other Diffserv PHBs, LE forwarding is 428 special, because often it is assumed that LE packets get only 429 forwarded in case of available resources at the output ports. The 430 previously mentioned redundancy data traffic could nicely use the 431 varying available residual bandwidth being utilized the by LE PHB, 432 but only if the previously specific requirements in the internal 433 implementation of the network devices are considered. 435 10. The Update to RFC 4594 437 [RFC4594] recommended to use CS1 as codepoint in section 4.10, 438 whereas CS1 was defined in [RFC2474] to have a higher precedence than 439 CS0, i.e., the default PHB. Consequently, Diffserv domains 440 implementing CS1 according to [RFC2474] will cause a priority 441 inversion for LE packets that contradicts with the original purpose 442 of LE. Therefore, every occurrence of the CS1 DSCP is replaced by 443 the LE DSCP. 445 Changes: 447 o This update to RFC 4594 removes the following entry from figure 3: 449 |---------------+---------+-------------+--------------------------| 450 | Low-Priority | CS1 | 001000 | Any flow that has no BW | 451 | Data | | | assurance | 452 ------------------------------------------------------------------ 454 and replaces this by the following entry: 456 |---------------+---------+-------------+--------------------------| 457 | Low-Priority | LE | 000001 | Any flow that has no BW | 458 | Data | | | assurance | 459 ------------------------------------------------------------------ 461 o This update to RFC 4594 extends the Notes text below figure 3 that 462 currently states "Notes for Figure 3: Default Forwarding (DF) and 463 Class Selector 0 (CS0) provide equivalent behavior and use the 464 same DS codepoint, '000000'." to state "Notes for Figure 3: 465 Default Forwarding (DF) and Class Selector 0 (CS0) provide 466 equivalent behavior and use the same DS codepoint, '000000'. The 467 prior recommendation to use the CS1 DSCP for Low-Priority Data has 468 been replaced by the current recommendation to use the LE DSCP, 469 '000001'." 471 o This update to RFC 4594 removes the following entry from figure 4: 473 |---------------+------+-------------------+---------+--------+----| 474 | Low-Priority | CS1 | Not applicable | RFC3662 | Rate | Yes| 475 | Data | | | | | | 476 ------------------------------------------------------------------ 477 and replaces this by the following entry: 479 |---------------+------+-------------------+---------+--------+----| 480 | Low-Priority | LE | Not applicable | RFCXXXX | Rate | Yes| 481 | Data | | | | | | 482 ------------------------------------------------------------------ 484 o Section 2.3 of [RFC4594] specifies: "In network segments that use 485 IP precedence marking, only one of the two service classes can be 486 supported, High-Throughput Data or Low-Priority Data. We 487 RECOMMEND that the DSCP value(s) of the unsupported service class 488 be changed to 000xx1 on ingress and changed back to original 489 value(s) on egress of the network segment that uses precedence 490 marking. For example, if Low-Priority Data is mapped to Standard 491 service class, then 000001 DSCP marking MAY be used to distinguish 492 it from Standard marked packets on egress." This document removes 493 this recommendation, because by using the herein defined LE DSCP 494 such remarking is not necessary. So even if Low-Priority Data is 495 unsupported (i.e., mapped to the default PHB) the LE DSCP should 496 be kept across the domain as RECOMMENDED in Section 8. That 497 removed text is replaced by: "In network segments that use IP 498 Precedence marking, the Low-Priority Data service class receives 499 the same Diffserv QoS as the Standard service class when the LE 500 DSCP is used for Low-Priority Data traffic. This is acceptable 501 behavior for the Low-Priority Data service class, although it is 502 not the preferred behavior." 504 o This document removes the following line of RFC 4594, 505 Section 4.10: "The RECOMMENDED DSCP marking is CS1 (Class Selector 506 1)." and replaces this with the following text: "The RECOMMENDED 507 DSCP marking is LE (Lower Effort), which replaces the prior 508 recommendation for CS1 (Class Selector 1) marking." 510 11. The Update to RFC 8325 512 Section 4.2.10 of RFC 8325 [RFC8325] specifies "[RFC3662] and 513 [RFC4594] both recommend Low-Priority Data be marked CS1 DSCP." 514 which is updated to "[RFC3662] recommends that Low-Priority Data be 515 marked CS1 DSCP. [RFC4594] as updated by [RFCXXXX] recommends Low- 516 Priority Data be marked LE DSCP." 518 This document removes the following paragraph of RFC 8325, 519 Section 4.2.10 because this document makes the anticipated change: 520 "Note: This marking recommendation may change in the future, as [LE- 521 PHB] defines a Lower Effort (LE) PHB for Low-Priority Data traffic 522 and recommends an additional DSCP for this traffic." 523 Section 4.2.10 of RFC 8325 [RFC8325] specifies "therefore, it is 524 RECOMMENDED to map Low-Priority Data traffic marked CS1 DSCP to UP 1" 525 which is updated to "therefore, it is RECOMMENDED to map Low-Priority 526 Data traffic marked with LE DSCP or legacy CS1 DSCP to UP 1" 528 This update to RFC 8325 replaces the following entry from figure 1: 530 +---------------+------+----------+-------------+--------------------+ 531 | Low-Priority | CS1 | RFC 3662 | 1 | AC_BK (Background) | 532 | Data | | | | | 533 +--------------------------------------------------------------------+ 535 by the following entries: 537 +---------------+------+----------+-------------+--------------------+ 538 | Low-Priority | LE | RFCXXXX | 1 | AC_BK (Background) | 539 | Data | | | | | 540 +--------------------------------------------------------------------+ 541 | Low-Priority | CS1 | RFC 3662 | 1 | AC_BK (Background) | 542 | Data (legacy) | | | | | 543 +--------------------------------------------------------------------+ 545 12. The Update to draft-ietf-tsvwg-rtcweb-qos 547 Section 5 of [I-D.ietf-tsvwg-rtcweb-qos] describes the Recommended 548 DSCP Values for WebRTC Applications 550 This update to [I-D.ietf-tsvwg-rtcweb-qos] replaces all occurrences 551 of CS1 with LE in Table 1: 553 +------------------------+-------+------+-------------+-------------+ 554 | Flow Type | Very | Low | Medium | High | 555 | | Low | | | | 556 +------------------------+-------+------+-------------+-------------+ 557 | Audio | LE | DF | EF (46) | EF (46) | 558 | | (1) | (0) | | | 559 | | | | | | 560 | Interactive Video with | LE | DF | AF42, AF43 | AF41, AF42 | 561 | or without Audio | (1) | (0) | (36, 38) | (34, 36) | 562 | | | | | | 563 | Non-Interactive Video | LE | DF | AF32, AF33 | AF31, AF32 | 564 | with or without Audio | (1) | (0) | (28, 30) | (26, 28) | 565 | | | | | | 566 | Data | LE | DF | AF11 | AF21 | 567 | | (1) | (0) | | | 568 +------------------------+-------+------+-------------+-------------+ 570 and updates the following paragraph: 572 "The above table assumes that packets marked with CS1 are treated as 573 "less than best effort", such as the LE behavior described in 574 [RFC3662]. However, the treatment of CS1 is implementation 575 dependent. If an implementation treats CS1 as other than "less than 576 best effort", then the actual priority (or, more precisely, the per- 577 hop-behavior) of the packets may be changed from what is intended. 578 It is common for CS1 to be treated the same as DF, so applications 579 and browsers using CS1 cannot assume that CS1 will be treated 580 differently than DF [RFC7657]. However, it is also possible per 581 [RFC2474] for CS1 traffic to be given better treatment than DF, thus 582 caution should be exercised when electing to use CS1. This is one of 583 the cases where marking packets using these recommendations can make 584 things worse." 586 as follows: 588 "The above table assumes that packets marked with LE are treated as 589 lower effort (i.e., "less than best effort"), such as the LE behavior 590 described in [RFCXXXX]. However, the treatment of LE is 591 implementation dependent. If an implementation treats LE as other 592 than "less than best effort", then the actual priority (or, more 593 precisely, the per- hop-behavior) of the packets may be changed from 594 what is intended. It is common for LE to be treated the same as DF, 595 so applications and browsers using LE cannot assume that LE will be 596 treated differently than DF [RFC7657]. During development of this 597 document, the CS1 DSCP was recommended for "very low" application 598 priority traffic; implementations that followed that recommendation 599 SHOULD be updated to use the LE DSCP instead of the CS1 DSCP." 601 13. IANA Considerations 603 This document assigns the Differentiated Services Field Codepoint 604 (DSCP) '000001' from the Differentiated Services Field Codepoints 605 (DSCP) registry (https://www.iana.org/assignments/dscp-registry/dscp- 606 registry.xhtml) (Pool 3, Codepoint Space xxxx01, Standards Action) to 607 the LE PHB. This document suggests to use a DSCP from Pool 3 in 608 order to avoid problems for other PHB marked flows to become 609 accidentally remarked as LE PHB, e.g., due to partial DSCP bleaching. 610 See [RFC8436] for re-classifying Pool 3 for Standards Action. 612 IANA is requested to update the registry as follows: 614 o Name: LE 616 o Value (Binary): 000001 618 o Value (Decimal): 1 619 o Reference: [RFC number of this memo] 621 14. Security Considerations 623 There are no specific security exposures for this PHB. Since it 624 defines a new class of low forwarding priority, remarking other 625 traffic as LE traffic may lead to quality-of-service degradation of 626 such traffic. Thus, any attacker that is able to modify the DSCP of 627 a packet to LE may carry out a downgrade attack. See the general 628 security considerations in [RFC2474] and [RFC2475]. 630 With respect to privacy, an attacker could use the information from 631 the DSCP to infer that the transferred (probably even encrypted) 632 content is considered of low priority or low urgency by a user, in 633 case the DSCP was set on the user's request. However, this disclosed 634 information is only useful if some form of identification happened at 635 the same time, see [RFC6973] for further details on general privacy 636 threats. 638 15. References 640 15.1. Normative References 642 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 643 Requirement Levels", BCP 14, RFC 2119, 644 DOI 10.17487/RFC2119, March 1997, 645 . 647 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 648 "Definition of the Differentiated Services Field (DS 649 Field) in the IPv4 and IPv6 Headers", RFC 2474, 650 DOI 10.17487/RFC2474, December 1998, 651 . 653 [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., 654 and W. Weiss, "An Architecture for Differentiated 655 Services", RFC 2475, DOI 10.17487/RFC2475, December 1998, 656 . 658 15.2. Informative References 660 [carlberg-lbe-2001] 661 Carlberg, K., Gevros, P., and J. Crowcroft, "Lower than 662 best effort: a design and implementation", SIGCOMM 663 Computer Communications Review Volume 31, Issue 2 664 supplement, April 2001, 665 . 667 [chown-lbe-2003] 668 Chown, T., Ferrari, T., Leinen, S., Sabatino, R., Simar, 669 N., and S. Venaas, "Less than Best Effort: Application 670 Scenarios and Experimental Results", In Proceedings of the 671 Second International Workshop on Quality of Service in 672 Multiservice IP Networks (QoS-IP 2003), Lecture Notes in 673 Computer Science, vol 2601. Springer, Berlin, 674 Heidelberg Pages 131-144, February 2003, 675 . 677 [draft-bless-diffserv-lbe-phb-00] 678 Bless, R. and K. Wehrle, "A Lower Than Best-Effort Per-Hop 679 Behavior", draft-bless-diffserv-lbe-phb-00 (work in 680 progress), September 1999, . 683 [I-D.ietf-tsvwg-rtcweb-qos] 684 Jones, P., Dhesikan, S., Jennings, C., and D. Druta, "DSCP 685 Packet Markings for WebRTC QoS", draft-ietf-tsvwg-rtcweb- 686 qos-18 (work in progress), August 2016. 688 [ietf99-secchi] 689 Secchi, R., Venne, A., and A. Custura, "Measurements 690 concerning the DSCP for a LE PHB", Presentation held at 691 99th IETF Meeting, TSVWG, Prague , July 2017, 692 . 696 [RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, 697 RFC 2914, DOI 10.17487/RFC2914, September 2000, 698 . 700 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 701 of Explicit Congestion Notification (ECN) to IP", 702 RFC 3168, DOI 10.17487/RFC3168, September 2001, 703 . 705 [RFC3439] Bush, R. and D. Meyer, "Some Internet Architectural 706 Guidelines and Philosophy", RFC 3439, 707 DOI 10.17487/RFC3439, December 2002, 708 . 710 [RFC3662] Bless, R., Nichols, K., and K. Wehrle, "A Lower Effort 711 Per-Domain Behavior (PDB) for Differentiated Services", 712 RFC 3662, DOI 10.17487/RFC3662, December 2003, 713 . 715 [RFC3754] Bless, R. and K. Wehrle, "IP Multicast in Differentiated 716 Services (DS) Networks", RFC 3754, DOI 10.17487/RFC3754, 717 April 2004, . 719 [RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration 720 Guidelines for DiffServ Service Classes", RFC 4594, 721 DOI 10.17487/RFC4594, August 2006, 722 . 724 [RFC5053] Luby, M., Shokrollahi, A., Watson, M., and T. Stockhammer, 725 "Raptor Forward Error Correction Scheme for Object 726 Delivery", RFC 5053, DOI 10.17487/RFC5053, October 2007, 727 . 729 [RFC6297] Welzl, M. and D. Ros, "A Survey of Lower-than-Best-Effort 730 Transport Protocols", RFC 6297, DOI 10.17487/RFC6297, June 731 2011, . 733 [RFC6817] Shalunov, S., Hazel, G., Iyengar, J., and M. Kuehlewind, 734 "Low Extra Delay Background Transport (LEDBAT)", RFC 6817, 735 DOI 10.17487/RFC6817, December 2012, 736 . 738 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 739 Morris, J., Hansen, M., and R. Smith, "Privacy 740 Considerations for Internet Protocols", RFC 6973, 741 DOI 10.17487/RFC6973, July 2013, 742 . 744 [RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage 745 Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, 746 March 2017, . 748 [RFC8100] Geib, R., Ed. and D. Black, "Diffserv-Interconnection 749 Classes and Practice", RFC 8100, DOI 10.17487/RFC8100, 750 March 2017, . 752 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 753 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 754 May 2017, . 756 [RFC8325] Szigeti, T., Henry, J., and F. Baker, "Mapping Diffserv to 757 IEEE 802.11", RFC 8325, DOI 10.17487/RFC8325, February 758 2018, . 760 [RFC8436] Fairhurst, G., "Update to IANA Registration Procedures for 761 Pool 3 Values in the Differentiated Services Field 762 Codepoints (DSCP) Registry", RFC 8436, 763 DOI 10.17487/RFC8436, August 2018, 764 . 766 Appendix A. History of the LE PHB 768 A first version of this PHB was suggested by Roland Bless and Klaus 769 Wehrle in September 1999 [draft-bless-diffserv-lbe-phb-00], named "A 770 Lower Than Best-Effort Per-Hop Behavior". After some discussion in 771 the Diffserv Working Group Brian Carpenter and Kathie Nichols 772 proposed a "bulk handling" per-domain behavior and believed a PHB was 773 not necessary. Eventually, "Lower Effort" was specified as per- 774 domain behavior and finally became [RFC3662]. More detailed 775 information about its history can be found in Section 10 of 776 [RFC3662]. 778 There are several other names in use for this type of PHB or 779 associated service classes. Well-known is the QBone Scavenger 780 Service (QBSS) that was proposed in March 2001 within the Internet2 781 QoS Working Group. Alternative names are "Lower-than-best-effort" 782 [carlberg-lbe-2001] or "Less-than-best-effort" [chown-lbe-2003]. 784 Appendix B. Acknowledgments 786 Since text is borrowed from earlier Internet-Drafts and RFCs the co- 787 authors of previous specifications are acknowledged here: Kathie 788 Nichols and Klaus Wehrle. David Black, Toerless Eckert, Gorry 789 Fairhurst, Ruediger Geib, and Spencer Dawkins provided helpful 790 comments and (also text) suggestions. 792 Appendix C. Change History 794 This section briefly lists changes between Internet-Draft versions 795 for convenience. 797 Changes in Version 07: 799 o revised some text for clarification according to comments from 800 Spencer Dawkins 802 Changes in Version 06: 804 o added Multicast Considerations section with input from Toerless 805 Eckert 807 o incorporated suggestions by David Black with respect to better 808 reflect legacy CS1 handling 810 Changes in Version 05: 812 o added scavenger service class into abstract 814 o added some more history 816 o added reference for "Myth of Over-Provisioning" in RFC3439 and 817 references to presentations w.r.t. codepoint choices 819 o added text to update draft-ietf-tsvwg-rtcweb-qos 821 o revised text on congestion control in case of remarking to BE 823 o added reference to DSCP measurement talk @IETF99 825 o small typo fixes 827 Changes in Version 04: 829 o Several editorial changes according to review from Gorry Fairhurst 831 o Changed the section structure a bit (moved subsections 1.1 and 1.2 832 into own sections 3 and 7 respectively) 834 o updated section 2 on requirements language 836 o added updates to RFC 8325 838 o tried to be more explicit what changes are required to RFCs 4594 839 and 8325 841 Changes in Version 03: 843 o Changed recommended codepoint to 000001 845 o Added text to explain the reasons for the DSCP choice 847 o Removed LE-min,LE-strict discussion 849 o Added one more potential use case: reporting errors or telemetry 850 data from OSs 852 o Added privacy considerations to the security section (not worth an 853 own section I think) 855 o Changed IANA considerations section 857 Changes in Version 02: 859 o Applied many editorial suggestions from David Black 861 o Added Multicast traffic use case 863 o Clarified what is required for deployment in section 1.2 864 (Deployment Considerations) 866 o Added text about implementations using AQMs and ECN usage 868 o Updated IANA section according to David Black's suggestions 870 o Revised text in the security section 872 o Changed copyright Notice to pre5378Trust200902 874 Changes in Version 01: 876 o Now obsoletes RFC 3662. 878 o Tried to be more precise in section 1.1 (Applicability) according 879 to R. Geib's suggestions, so rephrased several paragraphs. Added 880 text about congestion control 882 o Change section 2 (PHB Description) according to R. Geib's 883 suggestions. 885 o Added RFC 2119 language to several sentences. 887 o Detailed the description of remarking implications and 888 recommendations in Section 8. 890 o Added Section 10 to explicitly list changes with respect to RFC 891 4594, because this document will update it. 893 Appendix D. Note to RFC Editor 895 This section lists actions for the RFC editor during final 896 formatting. 898 o Please replace the occurrences of RFCXXXX in Section 10 and 899 Section 11 with the assigned RFC number for this document. 901 o Delete Appendix C. 903 o Delete this section. 905 Author's Address 907 Roland Bless 908 Karlsruhe Institute of Technology (KIT) 909 Kaiserstr. 12 910 Karlsruhe 76131 911 Germany 913 Phone: +49 721 608 46413 914 Email: roland.bless@kit.edu