idnits 2.17.1 draft-ietf-cdni-footprint-capabilities-semantics-11.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (March 4, 2016) is 2974 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) == Outdated reference: A later version (-27) exists of draft-ietf-cdni-logging-22 == Outdated reference: A later version (-21) exists of draft-ietf-cdni-metadata-12 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 CDNI J. Seedorf 3 Internet-Draft NEC 4 Intended status: Informational J. Peterson 5 Expires: September 5, 2016 Neustar 6 S. Previdi 7 Cisco 8 R. van Brandenburg 9 TNO 10 K. Ma 11 Ericsson 12 March 4, 2016 14 CDNI Request Routing: Footprint and Capabilities Semantics 15 draft-ietf-cdni-footprint-capabilities-semantics-11 17 Abstract 19 This document captures the semantics of the "Footprint and 20 Capabilities Advertisement" part of the CDNI Request Routing 21 interface, i.e., the desired meaning of "Footprint" and 22 "Capabilities" in the CDNI context, and what the "Footprint and 23 Capabilities Advertisement Interface (FCI)" offers within CDNI. The 24 document also provides guidelines for the CDNI FCI protocol. It 25 further defines a Base Advertisement Object, the necessary registries 26 for capabilities and footprints, and guidelines on how these 27 registries can be extended in the future. 29 Requirements Language 31 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 32 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 33 document are to be interpreted as described in RFC 2119 [RFC2119]. 35 Status of This Memo 37 This Internet-Draft is submitted in full conformance with the 38 provisions of BCP 78 and BCP 79. 40 Internet-Drafts are working documents of the Internet Engineering 41 Task Force (IETF). Note that other groups may also distribute 42 working documents as Internet-Drafts. The list of current Internet- 43 Drafts is at http://datatracker.ietf.org/drafts/current/. 45 Internet-Drafts are draft documents valid for a maximum of six months 46 and may be updated, replaced, or obsoleted by other documents at any 47 time. It is inappropriate to use Internet-Drafts as reference 48 material or to cite them other than as "work in progress." 49 This Internet-Draft will expire on September 5, 2016. 51 Copyright Notice 53 Copyright (c) 2016 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents 58 (http://trustee.ietf.org/license-info) in effect on the date of 59 publication of this document. Please review these documents 60 carefully, as they describe your rights and restrictions with respect 61 to this document. Code Components extracted from this document must 62 include Simplified BSD License text as described in Section 4.e of 63 the Trust Legal Provisions and are provided without warranty as 64 described in the Simplified BSD License. 66 Table of Contents 68 1. Introduction and Scope . . . . . . . . . . . . . . . . . . . 3 69 2. Design Decisions for Footprint and Capabilities . . . . . . . 4 70 2.1. Advertising Limited Coverage . . . . . . . . . . . . . . 4 71 2.2. Capabilities and Dynamic Data . . . . . . . . . . . . . . 5 72 2.3. Advertisement versus Queries . . . . . . . . . . . . . . 6 73 2.4. Avoiding or Handling 'cheating' dCDNs . . . . . . . . . . 7 74 2.5. Focusing on Main Use Cases . . . . . . . . . . . . . . . 7 75 3. Main Use Case to Consider . . . . . . . . . . . . . . . . . . 8 76 4. Semantics for Footprint Advertisement . . . . . . . . . . . . 8 77 5. Semantics for Capabilities Advertisement . . . . . . . . . . 11 78 6. Negotiation of Support for Optional Types of 79 Footprint/Capabilities . . . . . . . . . . . . . . . . . . . 13 80 7. Capability Advertisement Object . . . . . . . . . . . . . . . 14 81 7.1. Base Advertisement Object . . . . . . . . . . . . . . . . 14 82 7.2. Delivery Protocol Capability Object . . . . . . . . . . . 14 83 7.3. Acquisition Protocol Capability Object . . . . . . . . . 15 84 7.4. Redirection Mode Capability Object . . . . . . . . . . . 15 85 7.5. Capability Advertisement Object Serialization . . . . . . 15 86 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 87 8.1. CDNI Payload Types . . . . . . . . . . . . . . . . . . . 16 88 8.1.1. CDNI FCI DeliveryProtocol Payload Type . . . . . . . 17 89 8.1.2. CDNI FCI AcquisitionProtocol Payload Type . . . . . . 17 90 8.1.3. CDNI FCI RedirectionMode Payload Type . . . . . . . . 17 91 8.2. Redirection Mode Registry . . . . . . . . . . . . . . . . 17 92 9. Security Considerations . . . . . . . . . . . . . . . . . . . 18 93 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 94 10.1. Normative References . . . . . . . . . . . . . . . . . . 19 95 10.2. Informative References . . . . . . . . . . . . . . . . . 19 96 Appendix A. Acknowledgment . . . . . . . . . . . . . . . . . . . 20 97 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 99 1. Introduction and Scope 101 The CDNI working group is working on a set of protocols to enable the 102 interconnection of multiple CDNs. This CDN interconnection (CDNI) 103 can serve multiple purposes, as discussed in [RFC6770], for instance, 104 to extend the reach of a given CDN to areas in the network which are 105 not covered by this particular CDN. 107 The goal of this document is to achieve a clear understanding about 108 the semantics associated with the CDNI Request Routing Footprint & 109 Capabilities Advertisement Interface (from now on referred to as 110 FCI), in particular the type of information a downstream CDN 111 'advertises' regarding its footprint and capabilities. To narrow 112 down undecided aspects of these semantics, this document tries to 113 establish a common understanding of what the FCI needs to offer and 114 accomplish in the context of CDN Interconnection. 116 It is explicitly outside the scope of this document to decide on 117 specific protocols to use for the FCI. However, guidelines for such 118 FCI protocols are provided. 120 General assumptions in this document: 122 o The CDNs participating in the interconnected CDN have already 123 performed a boot strap process, i.e., they have connected to each 124 other, either directly or indirectly, and can exchange information 125 amongst each other. 127 o The upstream CDN (uCDN) receives footprint and/or capability 128 advertisements from a set of dCDNs. Footprint advertisement and 129 capability advertisement need not use the same underlying 130 protocol. 132 o The uCDN receives the initial request-routing request from the 133 endpoint requesting the resource. 135 The CDNI Problem Statement [RFC6707] describes the Request Routing 136 Interface as: "[enabling] a Request Routing function in an Upstream 137 CDN to query a Request Routing function in a Downstream CDN to 138 determine if the Downstream CDN is able (and willing) to accept the 139 delegated Content Request". In addition, the RFC says "the CDNI 140 Request Routing interface is also expected to enable a downstream CDN 141 to provide to the upstream CDN (static or dynamic) information (e.g., 142 resources, footprint, load) to facilitate selection of the downstream 143 CDN by the upstream CDN request routing system when processing 144 subsequent content requests from User Agents". It thus considers 145 "resources" and "load" as capabilities to be advertised by the 146 downstream CDN. 148 The range of different footprint definitions and possible 149 capabilities is very broad. Attempting to define a comprehensive 150 advertisement solution quickly becomes intractable. The CDNI 151 requirements draft [RFC7337] lists the specific requirements for the 152 CDNI Footprint & Capabilities Advertisement Interface in order to 153 disambiguate footprints and capabilities with respect to CDNI. This 154 document defines a common understanding of what the terms 'footprint' 155 and 'capabilities' mean in the context of CDNI, and details the 156 semantics of the footprint advertisement mechanism and the capability 157 advertisement mechanism. 159 2. Design Decisions for Footprint and Capabilities 161 A large part of the difficulty in discussing the FCI lies in 162 understanding what exactly is meant when trying to define footprint 163 in terms of "coverage" or "reachability." While the operators of 164 CDNs pick strategic locations to situate caches, a cache with a 165 public IPv4 address is reachable by any endpoint on the Internet 166 unless some policy enforcement precludes the use of the cache. 168 Some CDNs aspire to cover the entire world, which we will henceforth 169 call global CDNs. The footprint advertised by such a CDN in the CDNI 170 environment would, from a coverage or reachability perspective, 171 presumably cover all prefixes. Potentially more interesting for CDNI 172 use cases, however, are CDNs that claim a more limited coverage, but 173 seek to interconnect with other CDNs in order to create a single CDN 174 fabric which shares resources. 176 Futhermore, not all capabilities need to be footprint restricted. 177 Depending upon the use case, the optimal semantics of "footprints 178 with capability attributes" vs. "capabilities with footprint 179 restrictions" are not clear. 181 The key to understanding the semantics of footprint and capability 182 advertisement lies in understand why a dCDN would advertise a limited 183 coverage area, and how a uCDN would use such advertisements to decide 184 among one of several dCDNs. The following section will discuss some 185 of the trade-offs and design decisions that need to be decided upon 186 for the CDNI FCI. 188 2.1. Advertising Limited Coverage 190 The basic use case that would motivate a dCDN to advertise a limited 191 coverage is that the CDN was built to cover only a particular portion 192 of the Internet. For example, an ISP could purpose-build a CDN to 193 serve only their own customers by situating caches in close 194 topological proximity to high concentrations of their subscribers. 195 The ISP knows the prefixes it has allocated to end users and thus can 196 easily construct a list of prefixes that its caches were positioned 197 to serve. 199 When such a purpose-built CDN interconnects with other CDNs and 200 advertises its footprint to a uCDN, however, the original intended 201 coverage of the CDN might not represent its actual value to the 202 interconnection of CDNs. Consider an ISP-A and ISP-B that both field 203 their own CDNs, which they interconnect via CDNI. A given user E, 204 who is a customer of ISP-B, might happen to be topologically closer 205 to a cache fielded by ISP-A, if E happens to live in a region where 206 ISP-B has few customers and ISP-A has many. In this case, is it ISP- 207 A's CDN that "covers" E? If ISP-B's CDN has a failure condition, is 208 it up to the uCDN to understand that ISP-A's caches are potentially 209 available as back-ups - and if so, how does ISP-A advertise itself as 210 a "standby" for E? What about the case where CDNs advertising to the 211 same uCDN express overlapping coverage (for example, mixing global 212 and limited CDNs)? 214 The answers to these questions greatly depend on how much information 215 the uCDN wants to use to make a selection of a dCDN. If a uCDN has 216 three dCDNs to choose from that "cover" the IP address of user E, 217 obviously the uCDN might be interested to know how optimal the 218 coverage is from each of the dCDNs - coverage need not be binary, 219 either provided or not provided. dCDNs could advertise a coverage 220 "score," for example, and provided that they all reported scores 221 fairly on the same scale, uCDNs could use that to make their 222 topological optimality decision. Alternately, dCDNs could advertise 223 the IP addresses of their caches rather than prefix "coverage," and 224 let the uCDN decide for itself (based on its own topological 225 intelligence) which dCDN has better resources to serve a given user. 227 In summary, the semantics of advertising footprint depend on whether 228 such qualitative metrics for expressing footprint (such as the 229 coverage 'score' mentioned above) are included as part of the CDNI 230 FCI, or if the focus is just on 'binary' footprint. 232 2.2. Capabilities and Dynamic Data 234 In cases where the apparent footprints of dCDNs overlap, uCDNs might 235 also want to rely on other factors to evaluate the respective merits 236 of dCDNs. These include facts related to the caches themselves, to 237 the network where the cache is deployed, to the nature of the 238 resource sought, and to the administrative policies of the respective 239 networks. 241 In the absence of network-layer impediments to reaching caches, the 242 choice to limit coverage is necessarily an administrative policy. 243 Much policy needs to be agreed upon before CDNs can interconnect, 244 including questions of membership, compensation, volumes, and so on. 245 A uCDN certainly will factor these sorts of considerations into its 246 decision to select a dCDN, but there is probably little need for 247 dCDNs to actually advertise them through an interface - they will be 248 settled out-of-band as a precondition for interconnection. 250 Other facts about the dCDN would be expressed through the interface 251 to the uCDN. Some capabilities of a dCDN are static, and some are 252 highly dynamic. Expressing the total storage built into its caches, 253 for example, changes relatively rarely, whereas the amount of storage 254 in use at any given moment is highly volatile. Network bandwidth 255 similarly could be expressed as either total bandwidth available to a 256 cache, or based on the current state of the network. A cache can at 257 one moment lack a particular resource in storage, but have it the 258 next. 260 The semantics of the capabilities interface will depend on how much 261 of the dCDN state needs to be pushed to the uCDN and qualitatively 262 how often that information needs to be updated. 264 2.3. Advertisement versus Queries 266 In a CDNI environment, each dCDN shares some of its state with the 267 uCDN. The uCDN uses this information to build a unified picture of 268 all of the dCDNs available to it. In architectures that share 269 detailed capability information, the uCDN could perform the entire 270 request-routing operation down to selecting a particular cache in the 271 dCDN (note: within the current CDNI WG charter, such direct selection 272 of specific caches by the uCDN is out-of-scope). However, when the 273 uCDN needs to deal with many potential dCDNs, this approach does not 274 scale, especially for dCDNs with thousands or tens of thousands of 275 caches; the volume of updates to footprint and capability becomes 276 onerous. 278 Were the volume of FCI updates from dCDNs to exceed the volume of 279 requests to the uCDN, it might make more sense for the uCDN to query 280 dCDNs upon receiving requests (as is the case in the recursive 281 redirection mode described in [RFC7336]), instead of receiving 282 advertisements and tracking the state of dCDNs. The advantage of 283 querying dCDNs would be that much of the dynamic data that dCDNs 284 cannot share with the uCDN would now be factored into the uCDN's 285 decision. dCDNs need not replicate any state to the uCDN - uCDNs 286 could effectively operate in a stateless mode. 288 The semantics of both footprint and capability advertisement depend 289 on the service model here: are there cases where a synchronous query/ 290 response model would work better for the uCDN decision than a state 291 replication model? 293 2.4. Avoiding or Handling 'cheating' dCDNs 295 In a situation where more than one dCDN is willing to serve a given 296 end user request, it might be attractive for a dCDN to 'cheat' in the 297 sense that the dCDN provides inaccurate information to the uCDN in 298 order to convince the uCDN to select it over 'competing' dCDNs. It 299 could therefore be desirable to take away the incentive for dCDNs to 300 cheat (in information advertised) as much as possible. One option is 301 to make the information the dCDN advertises somehow verifiable for 302 the uCDN. On the other hand, a cheating dCDN might be avoided or 303 handled by the fact that there will be strong contractual agreements 304 between a uCDN and a dCDN, so that a dCDN would risk severe penalties 305 or legal consequences when caught cheating. 307 Overall, the information a dCDN advertises (in the long run) needs to 308 be somehow qualitatively verifiable by the uCDN, though possibly 309 through non-real-time out-of-band audits. It is probably an overly 310 strict requirement to mandate that such verification be possible 311 "immediately", i.e., during the request routing process itself. If 312 the uCDN can detect a cheating dCDN at a later stage, it might 313 suffice for the uCDN to "de-incentivize" cheating because it would 314 negatively affect the long-term business relationship with a 315 particular dCDN. 317 2.5. Focusing on Main Use Cases 319 To narrow down semantics for "footprint" and "capabilities" in the 320 CDNI context, it can be useful to initially focus on key use cases to 321 be addressed by the CDNI WG that are to be envisioned in the main 322 deployments in the foreseeable future. In this regard, a main 323 realistic use case is the existence of ISP-owned CDNs, which 324 essentially cover a certain operator's network. At the same time, 325 however, the possibility of overlapping footprints cannot be 326 excluded, i.e., the scenario where more than one dCDN claims it can 327 serve a given end user request. The ISPs can also choose to 328 interconnect with a fallback global CDN. 330 It seems reasonable to assume that in most use cases it is the uCDN 331 that makes the decision on selecting a certain dCDN for request 332 routing based on information the uCDN has received from this 333 particular dCDN. It can be assumed that 'cheating' CDNs will be 334 dealt with via means outside the scope of CDNI and that the 335 information advertised between CDNs is accurate. In addition, 336 excluding the use of qualitative information (e.g., cache proximity, 337 delivery latency, cache load) to predict the quality of delivery 338 would further simplify the use case allowing it to better focus on 339 the basic functionality of the FCI. 341 3. Main Use Case to Consider 343 Focusing on a main use case that contains a simple (yet somewhat 344 challenging), realistic, and generally imaginable scenario can help 345 in narrowing down the requirements for the CDNI FCI. To this end, 346 the following (simplified) use case can help in clarifying the 347 semantics of footprint and capabilities for CDNI. In particular, the 348 intention of the use case is to clarify what information needs to be 349 exchanged on the CDNI FCI, what types of information need to be 350 supported in a mandatory fashion (and which can be considered 351 optional), and what types of information need to be updated with 352 respect to a priori established CDNI contracts. 354 Use case: A given uCDN has several dCDNs. It selects one dCDN for 355 delivery protocol A and footprint 1 and another dCDN for delivery 356 protocol B and footprint 1. The dCDN that serves delivery protocol B 357 has a further, transitive (level-2) dCDN, that serves delivery 358 protocol B in a subset of footprint 1 where the first-level dCDN 359 cannot serve delivery protocol B itself. What happens if 360 capabilities change in the transitive level-2 dCDN that might affect 361 how the uCDN selects a level-1 dCDN (e.g., in case the level-2 dCDN 362 cannot serve delivery protocol B anymore)? How will these changes be 363 conveyed to the uCDN? In particular, what information does the uCDN 364 need to be able to select a new first-level dCDN, either for all of 365 footprint 1 or only for the subset of footprint 1 that the transitive 366 level-2 dCDN served on behalf of the first-level dCDN? 368 4. Semantics for Footprint Advertisement 370 Roughly speaking, "footprint" can be defined as "ability and 371 willingness to serve" by a downstream CDN. However, in addition to 372 simple "ability and willingness to serve", the uCDN could want 373 additional information to make a dCDN selection decision, e.g., "how 374 well" a given dCDN can actually serve a given end user request. The 375 "ability and willingness" to serve SHOULD be distinguished from the 376 subjective qualitative measurement of "how well" it was served. One 377 can imagine that such additional information is implicitly associated 378 with a given footprint, e.g., due to contractual agreements (e.g., 379 SLAs), business relationships, or perceived dCDN quality in the past. 380 As an alternative, such additional information could also be 381 explicitly tagged along with the footprint. 383 It is reasonable to assume that a significant part of the actual 384 footprint advertisement will happen in contractual agreements between 385 participating CDNs, i.e., prior to the advertisement phase using the 386 CDNI FCI. The reason for this assumption is that any contractual 387 agreement is likely to contain specifics about the dCDN coverage 388 (i.e., the dCDN footprint) to which the contractual agreement 389 applies. In particular, additional information to judge the delivery 390 quality associated with a given dCDN footprint might be defined in 391 contractual agreements (i.e. outside of the CDNI FCI). Further, one 392 can assume that dCDN contractual agreements about the delivery 393 quality associated with a given footprint will probably be based on 394 high-level aggregated statistics (i.e., not too detailed). 396 Given that a large part of footprint advertisement will actually 397 happen in contractual agreements, the semantics of CDNI footprint 398 advertisement refer to answering the following question: what exactly 399 still needs to be advertised by the CDNI FCI? For instance, updates 400 about temporal failures of part of a footprint can be useful 401 information to convey via the CDNI request routing interface. Such 402 information would provide updates on information previously agreed in 403 contracts between the participating CDNs. In other words, the CDNI 404 FCI is a means for a dCDN to provide changes/updates regarding a 405 footprint it has prior agreed to serve in a contract with a uCDN. 407 Generally speaking, one can imagine two categories of footprint to be 408 advertised by a dCDN: 410 o Footprint could be defined based on "coverage/reachability", where 411 coverage/reachability refers to a set of prefixes, a geographic 412 region, or similar boundary. The dCDN claims that it can cover/ 413 reach 'end user requests coming from this footprint'. 415 o Footprint could be defined based on "resources", where resources 416 refers to surrogates/caches a dCDN claims to have (e.g., the 417 location of surrogates/resources). The dCDN claims that 'from 418 this footprint' it can serve incoming end user requests. 420 For each of these footprint types, there are capabilities associated 421 with a given footprint, i.e., the capabilities (e.g., delivery 422 protocol, redirection mode, metadata) supported in the coverage area 423 for a "coverage/reachability" defined footprint, or the capabilities 424 of resources (e.g., delivery protocol, redirection mode, metadata 425 support) for a "resource" defined footprint. 427 It seems clear that "coverage/reachability" types of footprint MUST 428 be supported within CDNI. The following such types of footprint are 429 mandatory and MUST be supported by the CDNI FCI: 431 o List of ISO Country Codes 433 o List of AS numbers 435 o Set of IP-prefixes 437 A 'set of IP-prefixes' MUST be able to contain full IP addresses, 438 i.e., a /32 for IPv4 and a /128 for IPv6, as well as IP prefixes with 439 an arbitrary prefix length. There also MUST be support for multiple 440 IP address versions, i.e., IPv4 and IPv6, in such a footprint. 442 "Resource" types of footprints are more specific than "coverage/ 443 reachability" types of footprints, where the actual coverage/ 444 reachability are extrapolated from the resource location (e.g., 445 netmask applied to resource IP address to derive IP-prefix). The 446 specific methods for extrapolating coverage/reachability from 447 resource location are beyond the scope of this document. In the 448 degenerate case, the resource address could be specified as a 449 coverage/reachability type of footprint, in which case no 450 extrapolation is necessary. Resource types of footprints could 451 expose the internal structure of a CDN network which could be 452 undesirable. As such, the resource types of footprints are not 453 considered mandatory to support for CDNI. 455 For all of these mandatory-to-implement footprint types, the 456 footprints can be viewed as constraints for delegating requests to a 457 dCDN: A dCDN footprint advertisement tells the uCDN the limitations 458 for delegating a request to the dCDN. For IP prefixes or ASN(s), the 459 footprint signals to the uCDN that it SHOULD consider the dCDN a 460 candidate only if the IP address of the request routing source falls 461 within the prefix set (or ASN, respectively). The CDNI 462 specifications do not define how a given uCDN determines what address 463 ranges are in a particular ASN. Similarly, for country codes a uCDN 464 SHOULD only consider the dCDN a candidate if it covers the country of 465 the request routing source. The CDNI specifications do not define 466 how a given uCDN determines the country of the request routing 467 source. Multiple footprint constraints are additive, i.e., the 468 advertisement of different types of footprint narrows the dCDN 469 candidacy cumulatively. 471 In addition to these mandatory "coverage/reachability" types of 472 footprint, other optional "coverage/reachability" types of footprint 473 or "resource" types of footprint MAY be defined by future 474 specifications. To facilitate this, a clear process for specifying 475 optional footprint types in an IANA registry is specified in the CDNI 476 Metadata Footprint Types registry (defined in the CDNI Metadata 477 Interface document [I-D.ietf-cdni-metadata]). 479 Independent of the exact type of a footprint, a footprint might also 480 include the connectivity of a given dCDN to other CDNs that are able 481 to serve content to users on behalf of that dCDN, to cover cases with 482 cascaded CDNs. Further, the downstream CDN needs to be able to 483 express its footprint to an interested upstream CDN (uCDN) in a 484 comprehensive form, e.g., as a data set containing the complete 485 footprint. Making incremental updates, however, to express dynamic 486 changes in state is also desirable. 488 5. Semantics for Capabilities Advertisement 490 In general, the dCDN MUST be able to express its general capabilities 491 to the uCDN. These general capabilities could express if the dCDN 492 supports a given service, for instance, HTTP delivery, RTP/RTSP 493 delivery or RTMP. Furthermore, the dCDN MUST be able to express 494 particular capabilities for the delivery in a particular footprint 495 area. For example, the dCDN might in general offer RTMP but not in 496 some specific areas, either for maintenance reasons or because the 497 caches covering this particular area cannot deliver this type of 498 service. Hence, in certain cases footprint and capabilities are tied 499 together and cannot be interpreted independently from each other. In 500 such cases, i.e., where capabilities need to be expressed on a per 501 footprint basis, it could be beneficial to combine footprint and 502 capabilities advertisement. 504 A high-level and very rough semantic for capabilities is thus the 505 following: Capabilities are types of information that allow a uCDN to 506 determine if a downstream CDN is able (and willing) to accept (and 507 properly handle) a delegated content request. In addition, 508 Capabilities are characterized by the fact that this information can 509 change over time based on the state of the network or caches. 511 At a first glance, several broad categories of capabilities seem 512 useful to convey via an advertisement interface, however, advertising 513 capabilities that change highly dynamically (e.g., real-time delivery 514 performance metrics, CDN resource load, or other highly dynamically 515 changing QoS information) is beyond the scope for CDNI FCI. First, 516 out of the multitude of possible metrics and capabilities, it is hard 517 to agree on a subset and the precise metrics to be used. Second, and 518 perhaps more importantly, it seems infeasible to specify such highly 519 dynamically changing capabilities and the corresponding metrics 520 within the CDNI charter time-frame. 522 Useful capabilities refer to information that does not change highly 523 dynamically and which in many cases is absolutely necessary to decide 524 on a particular dCDN for a given end user request. For instance, if 525 an end user request concerns the delivery of a video file with a 526 certain protocol (e.g., RTMP), the uCDN needs to know if a given dCDN 527 has the capabilitity of supporting this delivery protocol. 529 Similar to footprint advertisement, it is reasonable to assume that a 530 significant part of the actual (resource) capabilities advertisement 531 will happen in contractual agreements between participating CDNs, 532 i.e., prior to the advertisement phase using the CDNI FCI. The role 533 of capability advertisement is hence rather to enable the dCDN to 534 update a uCDN on changes since a contract has been set up (e.g., in 535 case a new delivery protocol is suddenly being added to the list of 536 supported delivery protocols of a given dCDN, or in case a certain 537 delivery protocol is suddenly not being supported anymore due to 538 failures). Capabilities advertisement thus refers to conveying 539 information to a uCDN about changes/updates of certain capabilities 540 with respect to a given contract. 542 Given these semantics, it needs to be decided what exact capabilities 543 are useful and how these can be expressed. Since the details of CDNI 544 contracts are not known at the time of this writing (and the CDNI 545 interface are better off being agnostic to these contracts anyway), 546 it remains to be seen what capabilities will be used to define 547 agreements between CDNs in practice. One implication for 548 standardization could be to initially only specify a very limited set 549 of mandatory capabilities for advertisement and have on top of that a 550 flexible data model that allows exchanging additional capabilities 551 when needed. Still, agreement needs to be found on which 552 capabilities (if any) will be mandatory among CDNs. As discussed in 553 Section 2.5, finding the concrete answers to these questions can 554 benefit from focusing on a small number of key use cases that are 555 highly relevant and contain enough complexity to help in 556 understanding what concrete capabilities are needed to facilitate CDN 557 Interconnection. 559 Under the above considerations, the following capabilities seem 560 useful as 'base' capabilities, i.e., ones that are needed in any case 561 and therefore constitute mandatory capabilities that MUST be 562 supported by the CDNI FCI: 564 o Delivery Protocol (e.g., HTTP vs. RTMP) 566 o Acquisition Protocol (for aquiring content from a uCDN) 568 o Redirection Mode (e.g., DNS Redirection vs. HTTP Redirection as 569 discussed in [RFC7336]) 571 o CDNI Logging (i.e., supported logging fields) 573 o CDNI Metadata (i.e., supported Generic Metadata types) 574 It is not feasible to enumerate all the possible options for the 575 mandatory capabilities listed above (e.g., all the potential delivery 576 protocols or metadata options) or anticipate all the future needs for 577 additional capabilities. It would be unreasonable to burden the CDNI 578 FCI specification with defining each supported capability. Instead, 579 the CDNI FCI specification SHOULD define a generic protocol for 580 conveying any capability information (e.g. with common encoding, 581 error handling, and security mechanism; further requirements for the 582 CDNI FCI Advertisement Interface are listed in [RFC7337]). In this 583 respect, it seems reasonable to define a registry which initially 584 contains the mandatory capabilities listed above, but can be extended 585 as needs dictate. This document defines the registry (and the rules 586 for adding new entries to the registry) for the different capability 587 types (see Section 8). Each capability type MAY have a list of valid 588 values. Future specifications which define a given capability MUST 589 define any necessary registries (and the rules for adding new entries 590 to the registry) for the values advertised for a given capability 591 type. 593 The "CDNI Logging Fields Names" registry defines all supported 594 logging fields, including mandatory-to-implement logging fields. 595 Advertising support for mandatory-to-implement logging fields SHOULD 596 be supported but would be redundant. CDNs SHOULD NOT advertise 597 support for mandatory-to-implement logging fields. The following 598 logging fields are defined as optional in the CDNI Logging Interface 599 document [I-D.ietf-cdni-logging]: 601 o s-ccid 603 o s-sid 605 The CDNI Metadata Interface document [I-D.ietf-cdni-metadata] does 606 not define any optional GenericMetadata types. Advertiseing support 607 for mandatory-to-implement GenericMetadata types SHOULD be supported 608 but would be redundant. CDNs SHOULD NOT advertise support for 609 mandatory-to-implement GenericMetadata types. 611 6. Negotiation of Support for Optional Types of Footprint/Capabilities 613 The notion of optional types of footprint and capabilities implies 614 that certain implementations might not support all kinds of footprint 615 and capabilities. Therefore, any FCI solution protocol MUST define 616 how the support for optional types of footprint/capabilities will be 617 negotiated between a uCDN and a dCDN that use the particular FCI 618 protocol. In particular, any FCI solution protocol MUST specify how 619 to handle failure cases or non-supported types of footprint/ 620 capabilities. 622 In general, a uCDN MAY ignore capabilities or types of footprints it 623 does not understand; in this case it only selects a suitable 624 downstream CDN based on the types of capabilities and footprint it 625 understands. Similarly, if a dCDN does not use an optional 626 capability or footprint which is, however, supported by a uCDN, this 627 causes no problem for the FCI functionality because the uCDN decides 628 on the remaining capabilities/footprint information that is being 629 conveyed by the dCDN. 631 7. Capability Advertisement Object 633 To support extensibility, the FCI defines a generic base object 634 (similar to the CDNI Metadata interface GenericMetadata object) 635 [I-D.ietf-cdni-metadata] to facilitate a uniform set of mandatory 636 parsing requirements for all future FCI objects. 638 Future object definitions (e.g. regarding CDNI Metadata or Logging) 639 will build off the base object defined here, but will be specified in 640 separate documents. 642 7.1. Base Advertisement Object 644 The FCIBase object is an abstraction for managing individual CDNI 645 capabilities in an opaque manner. 647 Property: capability-type 649 Description: CDNI Capability object type. 651 Type: FCI specific CDNI Payload type (from the CDNI Payload 652 Types registry [RFC7736]) 654 Mandatory-to-Specify: Yes. 656 Property: capability-value 658 Description: CDNI Capability object. 660 Type: Format/Type is defined by the value of capability-type 661 property above. 663 Mandatory-to-Specify: Yes. 665 7.2. Delivery Protocol Capability Object 667 The Delivery Protocol capability object is used to indicate support 668 for one or more of the protocols listed in the CDNI Metadata Protocol 669 Types registry (defined in the CDNI Metadata Interface document 670 [I-D.ietf-cdni-metadata]). 672 Property: delivery-protocols 674 Description: List of supported CDNI Delivery Protocols. 676 Type: List of Protocol Types (from the CDNI Metadata Protocol 677 Types registry [I-D.ietf-cdni-metadata]) 679 Mandatory-to-Specify: Yes. 681 7.3. Acquisition Protocol Capability Object 683 The Acquisition Protocol capability object is used to indicate 684 support for one or more of the protocols listed in the CDNI Metadata 685 Protocol Types registry (defined in the CDNI Metadata Interface 686 document [I-D.ietf-cdni-metadata]). 688 Property: acquisition-protocols 690 Description: List of supported CDNI Acquisition Protocols. 692 Type: List of Protocol Types (from the CDNI Metadata Protocol 693 Types registry [I-D.ietf-cdni-metadata]) 695 Mandatory-to-Specify: Yes. 697 7.4. Redirection Mode Capability Object 699 The Redirection Mode capability object is used to indicate support 700 for one or more of the modes listed in the CDNI Capabilities 701 Redirection Modes registry (see Section 8.2). 703 Property: redirection-modes 705 Description: List of supported CDNI Redirection Modes. 707 Type: List of Redirection Modes (from Section 8.2) 709 Mandatory-to-Specify: Yes. 711 7.5. Capability Advertisement Object Serialization 713 The following shows an example of CDNI FCI Capability Advertisement 714 Object Serialization. 716 { 717 "capabilities": [ 718 { 719 "capability-type": "FCI.DeliveryProtocol" 720 "capability-value": { 721 "delivery-protocols": [ 722 "http1.1" 723 ] 724 } 725 }, 726 { 727 "capability-type": "FCI.AcquisitionProtocol" 728 "capability-value": { 729 "acquisition-protocols": [ 730 "http1.1", 731 "https1.1" 732 ] 733 } 734 }, 735 { 736 "capability-type": "FCI.RedirectionMode" 737 "capability-value": { 738 "redirection-modes": [ 739 "DNS-I", 740 "HTTP-I" 741 ] 742 } 743 } 744 ] 745 } 747 8. IANA Considerations 749 8.1. CDNI Payload Types 751 This document requests the registration of the following CDNI Payload 752 Types under the IANA CDNI Payload Type registry: 754 +-------------------------+---------------+ 755 | Payload Type | Specification | 756 +-------------------------+---------------+ 757 | FCI.DeliveryProtocol | RFCthis | 758 | | | 759 | FCI.AcquisitionProtocol | RFCthis | 760 | | | 761 | FCI.RedirectionMode | RFCthis | 762 +-------------------------+---------------+ 764 [RFC Editor: Please replace RFCthis with the published RFC number for 765 this document.] 767 8.1.1. CDNI FCI DeliveryProtocol Payload Type 769 Purpose: The purpose of this payload type is to distinguish FCI 770 advertisement objects for supported delivery protocols 772 Interface: FCI 774 Encoding: see Section 7 776 8.1.2. CDNI FCI AcquisitionProtocol Payload Type 778 Purpose: The purpose of this payload type is to distinguish FCI 779 advertisement objects for supported acquisition protocols 781 Interface: FCI 783 Encoding: see Section 7 785 8.1.3. CDNI FCI RedirectionMode Payload Type 787 Purpose: The purpose of this payload type is to distinguish FCI 788 advertisement objects for supported redirection modes 790 Interface: FCI 792 Encoding: see Section 7 794 8.2. Redirection Mode Registry 796 The IANA is requested to create a new "CDNI Capabilities Redirection 797 Modes" registry in the "Content Delivery Networks Interconnection 798 (CDNI) Parameters" category. The "CDNI Capabilities Redirection 799 Modes" namespace defines the valid redirection modes that can be 800 advertised as supported by a CDN. Additions to the Redirection Mode 801 namespace conform to the "IETF Review" policy as defined in 802 [RFC5226]. 804 The following table defines the initial Redirection Modes: 806 +------------------+----------------------------------+---------+ 807 | Redirection Mode | Description | RFC | 808 +------------------+----------------------------------+---------+ 809 | DNS-I | Iterative DNS-based Redirection | RFCthis | 810 | | | | 811 | DNS-R | Recursive DNS-based Redirection | RFCthis | 812 | | | | 813 | HTTP-I | Iterative HTTP-based Redirection | RFCthis | 814 | | | | 815 | HTTP-R | Recursive HTTP-based Redirection | RFCthis | 816 +------------------+----------------------------------+---------+ 818 [RFC Editor: Please replace RFCthis with the published RFC number for 819 this document.] 821 9. Security Considerations 823 This specification describes the semantics for capabilities and 824 footprint advertisement objects across interconnected CDNs. It does 825 not, however, specify a concrete protocol for transporting those 826 objects. Specific security mechanisms can only be selected for 827 concrete protocols that instantiate these semantics. This document 828 does, however, place some high-level security constraints on such 829 protocols. 831 All protocols that implement these semantics are REQUIRED to provide 832 integrity and authentication services. Without authentication and 833 integrity, an attacker could trivially deny service by forging a 834 footprint advertisement from a dCDN which claims the network has no 835 footprint or capability. This would prevent the uCDN from delegating 836 any requests to the dCDN. Since a pre-existing relationship between 837 all dCDNs and uCDNs is assumed by CDNI, the exchange of any necessary 838 credentials could be conducted before the FCI interface is brought 839 online. The authorization decision to accept advertisements would 840 also follow this pre-existing relationship and any contractual 841 obligations that it stipulates. 843 It is not believed that there are any serious privacy risks in 844 sharing footprint or capability information: it will represent highly 845 aggregated data about networks and, at best, policy-related 846 information about media, rather than any personally identifying 847 information. However, particular dCDNs could be willing to share 848 information about their footprint with a uCDN but not with other, 849 competing dCDNs. For example, if a dCDN incurs an outage that 850 reduces footprint coverage temporarily, that could be information the 851 dCDN would want to share confidentially with the uCDN. Protocols 852 implementing these semantics SHOULD provide confidentiality services. 854 As specified in this document, the security requirements of the FCI 855 could be met by hop-by-hop transport-layer security mechanisms 856 coupled with domain certificates as credentials. There is no 857 apparent need for further object-level security in this framework, as 858 the trust relationships it defines are bilateral relationships 859 between uCDNs and dCDNs rather than transitive relationships. 861 10. References 863 10.1. Normative References 865 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 866 Requirement Levels", BCP 14, RFC 2119, 867 DOI 10.17487/RFC2119, March 1997, 868 . 870 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 871 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 872 DOI 10.17487/RFC5226, May 2008, 873 . 875 10.2. Informative References 877 [I-D.ietf-cdni-logging] 878 Faucheur, F., Bertrand, G., Oprescu, I., and R. 879 Peterkofsky, "CDNI Logging Interface", draft-ietf-cdni- 880 logging-22 (work in progress), March 2016. 882 [I-D.ietf-cdni-metadata] 883 Niven-Jenkins, B., Murray, R., Caulfield, M., and K. Ma, 884 "CDN Interconnection Metadata", draft-ietf-cdni- 885 metadata-12 (work in progress), October 2015. 887 [RFC6707] Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content 888 Distribution Network Interconnection (CDNI) Problem 889 Statement", RFC 6707, DOI 10.17487/RFC6707, September 890 2012, . 892 [RFC6770] Bertrand, G., Ed., Stephan, E., Burbridge, T., Eardley, 893 P., Ma, K., and G. Watson, "Use Cases for Content Delivery 894 Network Interconnection", RFC 6770, DOI 10.17487/RFC6770, 895 November 2012, . 897 [RFC7336] Peterson, L., Davie, B., and R. van Brandenburg, Ed., 898 "Framework for Content Distribution Network 899 Interconnection (CDNI)", RFC 7336, DOI 10.17487/RFC7336, 900 August 2014, . 902 [RFC7337] Leung, K., Ed. and Y. Lee, Ed., "Content Distribution 903 Network Interconnection (CDNI) Requirements", RFC 7337, 904 DOI 10.17487/RFC7337, August 2014, 905 . 907 [RFC7736] Ma, K., "Content Delivery Network Interconnection (CDNI) 908 Media Type Registration", RFC 7736, DOI 10.17487/RFC7736, 909 December 2015, . 911 Appendix A. Acknowledgment 913 Jan Seedorf is partially supported by the GreenICN project (GreenICN: 914 Architecture and Applications of Green Information Centric 915 Networking), a research project supported jointly by the European 916 Commission under its 7th Framework Program (contract no. 608518) and 917 the National Institute of Information and Communications Technology 918 (NICT) in Japan (contract no. 167). The views and conclusions 919 contained herein are those of the authors and should not be 920 interpreted as necessarily representing the official policies or 921 endorsements, either expressed or implied, of the GreenICN project, 922 the European Commission, or NICT. 924 Martin Stiemerling provided initial input to this document and 925 valuable comments to the ongoing discussions among the authors of 926 this document. Thanks to Francois Le Faucheur and Scott Wainner for 927 providing valuable comments and suggestions to the text. 929 Authors' Addresses 931 Jan Seedorf 932 NEC 933 Kurfuerstenanlage 36 934 Heidelberg 69115 935 Germany 937 Phone: +49 6221 4342 221 938 Fax: +49 6221 4342 155 939 Email: seedorf@neclab.eu 941 Jon Peterson 942 NeuStar 943 1800 Sutter St Suite 570 944 Concord CA 94520 945 USA 947 Email: jon.peterson@neustar.biz 948 Stefano Previdi 949 Cisco Systems 950 Via Del Serafico 200 951 Rome 0144 952 Italy 954 Email: sprevidi@cisco.com 956 Ray van Brandenburg 957 TNO 958 Brassersplein 2 959 Delft 2612CT 960 The Netherlands 962 Phone: +31-88-866-7000 963 Email: ray.vanbrandenburg@tno.nl 965 Kevin J. Ma 966 Ericsson 967 43 Nagog Park 968 Acton, MA 01720 969 USA 971 Phone: +1 978-844-5100 972 Email: kevin.j.ma@ericsson.com