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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** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) == Outdated reference: A later version (-27) exists of draft-ietf-cdni-logging-21 == Outdated reference: A later version (-21) exists of draft-ietf-cdni-metadata-12 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 1 comment (--).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: May 6, 2016 Neustar 6 S. Previdi 7 Cisco 8 R. van Brandenburg 9 TNO 10 K. Ma 11 Ericsson 12 November 3, 2015 14 CDNI Request Routing: Footprint and Capabilities Semantics 15 draft-ietf-cdni-footprint-capabilities-semantics-09 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 how these registries 27 may 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 May 6, 2016. 51 Copyright Notice 53 Copyright (c) 2015 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 AcuiqisitionProtocol 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 to a CDN federation. This CDN- 103 federation should serve multiple purposes, as discussed in [RFC6770], 104 for instance, to extend the reach of a given CDN to areas in the 105 network which are 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 should 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 CDN federation 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 uCDN has received footprint and/or capability advertisements 128 from a set of dCDNs. Footprint advertisement and capability 129 advertisement need not use the same underlying protocol. 131 o The upstream CDN (uCDN) receives the initial request-routing 132 request from the endpoint requesting the resource. 134 The CDNI Problem Statement [RFC6707] describes footprint and 135 capabilities advertisement as: "[enabling] a Request Routing function 136 in an Upstream CDN to query a Request Routing function in a 137 Downstream CDN to determine if the Downstream CDN is able (and 138 willing) to accept the delegated Content Request". In addition, the 139 RFC says "the CDNI Request Routing interface is also expected to 140 enable a downstream CDN to provide to the upstream CDN (static or 141 dynamic) information (e.g., resources, footprint, load) to facilitate 142 selection of the downstream CDN by the upstream CDN request routing 143 system when processing subsequent content requests from User Agents". 145 It thus considers "resources" and "load" as capabilities to be 146 advertised by the 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 detail 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 federate with other CDNs in order to create a single CDN 174 fabric which shares resources. 176 Futhermore, not all capabilities need 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 joins a federation, and advertises its 200 footprint to a uCDN, however, the original intended coverage of the 201 CDN might not represent its actual value to the federation of CDNs. 202 Consider an ISP-A and ISP-B that both field their own CDNs, which 203 they federate through CDNI. A given user E, who is customer of ISP- 204 B, might happen to be topologically closest to a cache fielded by 205 ISP-A, if E happens to live in a region where ISP-B has few customers 206 and ISP-A has many. In this case, should ISP-A's CDN "cover" E? If 207 ISP-B's CDN has a failure condition, should the uCDN understand that 208 ISP-A's caches are potentially available back-ups - and if so, how 209 does ISP-A advertise itself as a "standby" for E? What about the 210 case where CDNs advertising to the same uCDN express overlapping 211 coverage (for example, a federation mixing global and limited CDNs)? 213 The answers to these questions greatly depend on how much information 214 the uCDN wants to use to make a selection of a dCDN. If a uCDN has 215 three dCDNs to choose from that "cover" the IP address of user E, 216 obviously the uCDN might be interested to know how optimal the 217 coverage is from each of the dCDNs - coverage need not be binary, 218 either provided or not provided. dCDNs could advertise a coverage 219 "score," for example, and provided that they all reported scores 220 fairly on the same scale, uCDNs could use that to make their 221 topological optimality decision. Alternately, dCDNs could advertise 222 the IP addresses of their caches rather than prefix "coverage," and 223 let the uCDN decide for itself (based on its own topological 224 intelligence) which dCDN has better resources to serve a given user. 226 In summary, the semantics of advertising footprint depend on whether 227 such qualitative metrics for expressing footprint (such as the 228 coverage 'score' mentioned above) should be part of the CDNI FCI, or 229 if it should focus just on 'binary' footprint. 231 2.2. Capabilities and Dynamic Data 233 In cases where the apparent footprints of dCDNs overlap, uCDNs might 234 also want to rely on other factors to evaluate the respective merits 235 of dCDNs. These include facts related to the caches themselves, to 236 the network where the cache is deployed, to the nature of the 237 resource sought, and to the administrative policies of the respective 238 networks. 240 In the absence of network-layer impediments to reaching caches, the 241 choice to limit coverage is necessarily an administrative policy. 242 Much policy must be agreed upon before CDNs can merge into 243 federations, including questions of membership, compensation, 244 volumes, and so on. A uCDN certainly will factor these sorts of 245 considerations into its decision to select a dCDN, but there is 246 probably little need for dCDNs to actually advertise them through an 247 interface - they will be settled out-of-band as a precondition for 248 federating. 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 may 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 should be updated. 264 2.3. Advertisement versus Queries 266 In a federated CDN environment, each dCDN shares some of its state 267 with the uCDN. The uCDN uses this information to build a unified 268 picture of all of the dCDNs available to it. In architectures that 269 share detailed capability information, the uCDN could perform the 270 entire request-routing operation down to selecting a particular cache 271 in the dCDN (note: within the current CDNI WG charter, such direct 272 selection of specific caches by the uCDN is out-of-scope). However, 273 when the uCDN must deal with many potential dCDNs, this approach does 274 not scale, especially for dCDNs with thousands or tens of thousands 275 of 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. One 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 should (in the long run) 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 should 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 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 should not be 326 excluded, i.e., the scenario where more than one dCDN claims it can 327 serve a given end user request. The ISPs may also choose to federate 328 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 may 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 should 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 may wish to have 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 must also 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 may expose 451 the internal structure of a CDN network which may be undesirable. As 452 such, the resource types of footprints are not considered mandatory 453 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 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 may be 481 able to serve content to users on behalf of that dCDN, to cover cases 482 where there is a transitive CDN interconnection. Further, the 483 downstream CDN must be able to express its footprint to an interested 484 upstream CDN (uCDN) in a comprehensive form, e.g., as a data set 485 containing the complete footprint. Making incremental updates, 486 however, to express dynamic 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 must be expressed on a per 501 footprint basis, it may 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 may 509 possibly change over time based on the state of the network or 510 caches. 512 At a first glance, several broad categories of capabilities seem 513 useful to convey via an advertisement interface, however, advertising 514 capabilities that change highly dynamically (e.g., real-time delivery 515 performance metrics, CDN resource load, or other highly dynamically 516 changing QoS information) should probably not be in scope for the 517 CDNI FCI. First, out of the multitude of possible metrics and 518 capabilities, it is hard to agree on a subset and the precise metrics 519 to be used. Second, and perhaps more importantly, it seems not 520 feasible to specify such highly dynamically changing capabilities and 521 the corresponding metrics within the CDNI charter time-frame. 523 Useful capabilities refer to information that does not change highly 524 dynamically and which in many cases is absolutely necessary to decide 525 on a particular dCDN for a given end user request. For instance, if 526 an end user request concerns the delivery of a video file with a 527 certain protocol (e.g., RTMP), the uCDN needs to know if a given dCDN 528 has the capabilitity of supporting this delivery protocol. 530 Similar to footprint advertisement, it is reasonable to assume that a 531 significant part of the actual (resource) capabilities advertisement 532 will happen in contractual agreements between participating CDNs, 533 i.e., prior to the advertisement phase using the CDNI FCI. The role 534 of capability advertisement is hence rather to enable the dCDN to 535 update a uCDN on changes since a contract has been set up (e.g., in 536 case a new delivery protocol is suddenly being added to the list of 537 supported delivery protocols of a given dCDN, or in case a certain 538 delivery protocol is suddenly not being supported anymore due to 539 failures). Capabilities advertisement thus refers to conveying 540 information to a uCDN about changes/updates of certain capabilities 541 with respect to a given contract. 543 Given these semantics, it needs to be decided what exact capabilities 544 are useful and how these can be expressed. Since the details of CDNI 545 contracts are not known at the time of this writing (and the CDNI 546 interface should probably be agnostic to these contracts anyway), it 547 remains to be seen what capabilities will be used to define 548 agreements between CDNs in practice. One implication for 549 standardization may be to initially only specify a very limited set 550 of mandatory capabilities for advertisement and have on top of that a 551 flexible data model that allows exchanging additional capabilities 552 when needed. Still, agreement needs to be found on which 553 capabilities (if any) should be mandatory among CDNs. As discussed 554 in Section 2.5, finding the concrete answers to these questions can 555 benefit from focusing on a small number of key use cases that are 556 highly relevant and contain enough complexity to help in 557 understanding what concrete capabilities are needed to facilitate CDN 558 Interconnection. 560 Under the above considerations, the following capabilities seem 561 useful as 'base' capabilities, i.e., ones that are needed in any case 562 and therefore constitute mandatory capabilities that MUST be 563 supported by the CDNI FCI: 565 o Delivery Protocol (e.g., HTTP vs. RTMP) 567 o Acquisition Protocol (for aquiring content from a uCDN) 569 o Redirection Mode (e.g., DNS Redirection vs. HTTP Redirection as 570 discussed in [RFC7336]) 572 o CDNI Logging (i.e., supported logging fields) 574 o CDNI Metadata (i.e., supported Generic Metadata types) 575 It is not feasable to enumerate all the possible options for the 576 mandatory capabilities listed above (e.g., all the potential delivery 577 protocols or metadata options) or anticipate all the future needs for 578 additional capabilities. It would be unreasonable to burden the CDNI 579 FCI specification with defining each supported capability. Instead, 580 the CDNI FCI specification should define a generic protocol for 581 conveying any capability information (e.g. with common encoding, 582 error handling, and security mechanism; further requirements for the 583 CDNI FCI Advertisement Interface are listed in [RFC7337]). In this 584 respect, it seems reasonable to define a registry which initially 585 contains the mandatory capabilities listed above, but may be extended 586 as needs dictate. This document defines the registry (and the rules 587 for adding new entries to the registry) for the different capability 588 types (see Section 8). Each capability type MAY have a list of valid 589 values. Future specifications which define a given capability SHOULD 590 define any necessary registries (and the rules for adding new entries 591 to the registry) for the values advertised for a given capability 592 type. 594 The "CDNI Logging Fields Names" registry defines all supported 595 logging fields, including mandatory-to-implement logging fields. 596 Advertising support for mandatory-to-implement logging fields SHOULD 597 be supported but would be redundant. CDNs SHOULD NOT advertise 598 support for mandatory-to-implement logging fields. The following 599 logging fields are defined as optional in the CDNI Logging Interface 600 document [I-D.ietf-cdni-logging]: 602 o s-ccid 604 o s-sid 606 The CDNI Metadata Interface document [I-D.ietf-cdni-metadata] does 607 not define any optional GenericMetadata types. Advertiseing support 608 for mandatory-to-implement GenericMetadata types SHOULD be supported 609 but would be redundant. CDNs SHOULD NOT advertise support for 610 mandatory-to-implement GenericMetadata types. 612 6. Negotiation of Support for Optional Types of Footprint/Capabilities 614 The notion of optional types of footprint and capabilities implies 615 that certain implementations may not support all kinds of footprint 616 and capabilities. Therefore, any FCI solution protocol must define 617 how the support for optional types of footprint/capabilities will be 618 negotiated between a uCDN and a dCDN that use the particular FCI 619 protocol. In particular, any FCI solution protocol needs to specify 620 how to handle failure cases or non-supported types of footprint/ 621 capabilities. 623 In general, a uCDN may ignore capabilities or types of footprints it 624 does not understand; in this case it only selects a suitable 625 downstream CDN based on the types of capabilities and footprint it 626 understands. Similarly, if a dCDN does not use an optional 627 capability or footprint which is, however, supported by a uCDN, this 628 causes no problem for the FCI functionality because the uCDN decides 629 on the remaining capabilities/footprint information that is being 630 conveyed by the dCDN. 632 7. Capability Advertisement Object 634 To support extensibility, the FCI defines a generic base object 635 (similar to the CDNI Metadata interface GenericMetadata object) 636 [I-D.ietf-cdni-metadata] to facilitate a uniform set of mandatory 637 parsing requirements for all future FCI objects. 639 Future object definitions (e.g. regarding CDNI Metadata or Logging) 640 will build off the base object defined here, but will be specified in 641 separate documents. 643 7.1. Base Advertisement Object 645 The FCIBase object is an abstraction for managing individual CDNI 646 capabilities in an opaque manner. 648 Property: capability-type 650 Description: CDNI Capability object type. 652 Type: FCI specific CDNI Payload type (from the CDNI Payload 653 Types registry [I-D.ietf-cdni-media-type]) 655 Mandatory-to-Specify: Yes. 657 Property: capability-value 659 Description: CDNI Capability object. 661 Type: Format/Type is defined by the value of capability-type 662 property above. 664 Mandatory-to-Specify: Yes. 666 7.2. Delivery Protocol Capability Object 668 The Delivery Protocol capability object is used to indicate support 669 for one or more of the protocols listed in the CDNI Metadata Protocol 670 Types registry (defined in the CDNI Metadata Interface document 671 [I-D.ietf-cdni-metadata]). 673 Property: delivery-protocols 675 Description: List of supported CDNI Delivery Protocols. 677 Type: List of Protocol Types (from the CDNI Metadata Protocol 678 Types registry [I-D.ietf-cdni-metadata]) 680 Mandatory-to-Specify: Yes. 682 7.3. Acquisition Protocol Capability Object 684 The Acquisition Protocol capability object is used to indicate 685 support for one or more of the protocols listed in the CDNI Metadata 686 Protocol Types registry (defined in the CDNI Metadata Interface 687 document [I-D.ietf-cdni-metadata]). 689 Property: acquisition-protocols 691 Description: List of supported CDNI Acquisition Protocols. 693 Type: List of Protocol Types (from the CDNI Metadata Protocol 694 Types registry [I-D.ietf-cdni-metadata]) 696 Mandatory-to-Specify: Yes. 698 7.4. Redirection Mode Capability Object 700 The Redirection Mode capability object is used to indicate support 701 for one or more of the modes listed in the CDNI Capabilities 702 Redirection Modes registry (see Section 8.2). 704 Property: redirection-modes 706 Description: List of supported CDNI Redirection Modes. 708 Type: List of Redirection Modes (from Section 8.2) 710 Mandatory-to-Specify: Yes. 712 7.5. Capability Advertisement Object Serialization 714 The following shows an example of CDNI FCI Capability Advertisement 715 Object Serialization. 717 { 718 "capabilities": [ 719 { 720 "capability-type": "FCI.DeliveryProtocol" 721 "capability-value": { 722 "delivery-protocols": [ 723 "http1.1" 724 ] 725 } 726 }, 727 { 728 "capability-type": "FCI.AcquisitionProtocol" 729 "capability-value": { 730 "acquisition-protocols": [ 731 "http1.1", 732 "https1.1" 733 ] 734 } 735 }, 736 { 737 "capability-type": "FCI.RedirectionMode" 738 "capability-value": { 739 "redirection-modes": [ 740 "DNS-I", 741 "HTTP-I" 742 ] 743 } 744 } 745 ] 746 } 748 8. IANA Considerations 750 8.1. CDNI Payload Types 752 This document requests the registration of the following CDNI Payload 753 Types under the IANA CDNI Payload Type registry: 755 +-------------------------+---------------+ 756 | Payload Type | Specification | 757 +-------------------------+---------------+ 758 | FCI.DeliveryProtocol | RFCthis | 759 | | | 760 | FCI.AcquisitionProtocol | RFCthis | 761 | | | 762 | FCI.RedirectionMode | RFCthis | 763 +-------------------------+---------------+ 765 [RFC Editor: Please replace RFCthis with the published RFC number for 766 this document.] 768 8.1.1. CDNI FCI DeliveryProtocol Payload Type 770 Purpose: The purpose of this payload type is to distinguish FCI 771 advertisement objects for supported delivery protocols 773 Interface: FCI 775 Encoding: see Section 7 777 8.1.2. CDNI FCI AcuiqisitionProtocol Payload Type 779 Purpose: The purpose of this payload type is to distinguish FCI 780 advertisement objects for supported acquisition protocols 782 Interface: FCI 784 Encoding: see Section 7 786 8.1.3. CDNI FCI RedirectionMode Payload Type 788 Purpose: The purpose of this payload type is to distinguish FCI 789 advertisement objects for supported redirection modes 791 Interface: FCI 793 Encoding: see Section 7 795 8.2. Redirection Mode Registry 797 The IANA is requested to create a new "CDNI Capabilities Redirection 798 Modes" registry in the "Content Delivery Networks Interconnection 799 (CDNI) Parameters" category. The "CDNI Capabilities Redirection 800 Modes" namespace defines the valid redirection modes that may be 801 advertised as supported by a CDN. Additions to the Redirection Mode 802 namespace conform to the "IETF Review" policy as defined in 803 [RFC5226]. 805 The following table defines the initial Redirection Modes: 807 +------------------+----------------------------------+---------+ 808 | Redirection Mode | Description | RFC | 809 +------------------+----------------------------------+---------+ 810 | DNS-I | Iterative DNS-based Redirection | RFCthis | 811 | | | | 812 | DNS-R | Recursive DNS-based Redirection | RFCthis | 813 | | | | 814 | HTTP-I | Iterative HTTP-based Redirection | RFCthis | 815 | | | | 816 | HTTP-R | Recursive HTTP-based Redirection | RFCthis | 817 +------------------+----------------------------------+---------+ 819 [RFC Editor: Please replace RFCthis with the published RFC number for 820 this document.] 822 9. Security Considerations 824 This specification describes the semantics for capabilities and 825 footprint advertisement objects in content distribution networks. It 826 does not, however, specify a concrete protocol for transporting those 827 objects. Specific security mechanisms can only be selected for 828 concrete protocols that instantiate these semantics. This document 829 does, however, place some high-level security constraints on such 830 protocols. 832 All protocols that implement these semantics are REQUIRED to provide 833 integrity and authentication services. Without authentication and 834 integrity, an attacker could trivially deny service by forging a 835 footprint advertisement from a dCDN which claims the network has no 836 footprint or capability. This would prevent the uCDN from delegating 837 any requests to the dCDN. Since a pre-existing relationship between 838 all dCDNs and uCDNs is assumed by CDNi, the exchange of any necessary 839 credentials could be conducted before the FCI interface is brought 840 online. The authorization decision to accept advertisements would 841 also follow this pre-existing relationship and any contractual 842 obligations that it stipulates. 844 It is not believed that there are any serious privacy risks in 845 sharing footprint or capability information: it will represent highly 846 aggregated data about networks and, at best, policy-related 847 information about media, rather than any personally identifying 848 information. However, particular dCDNs may wish to share information 849 about their footprint with a uCDN but not with other, competing 850 dCDNs. For example, if a dCDN incurs an outage that reduces 851 footprint coverage temporarily, that may be information the dCDN 852 would want to share confidentially with the uCDN. Protocols 853 implementing these semantics SHOULD provide confidentiality services. 855 As specified in this document, the security requirements of the FCI 856 could be met by hop-by-hop transport-layer security mechanisms 857 coupled with domain certificates as credentials. There is no 858 apparent need for further object-level security in this framework, as 859 the trust relationships it defines are bilateral relationships 860 between uCDNs and dCDNs rather than transitive relationships. 862 10. References 864 10.1. Normative References 866 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 867 Requirement Levels", BCP 14, RFC 2119, 868 DOI 10.17487/RFC2119, March 1997, 869 . 871 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 872 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 873 DOI 10.17487/RFC5226, May 2008, 874 . 876 10.2. Informative References 878 [I-D.ietf-cdni-logging] 879 Faucheur, F., Bertrand, G., Oprescu, I., and R. 880 Peterkofsky, "CDNI Logging Interface", draft-ietf-cdni- 881 logging-21 (work in progress), November 2015. 883 [I-D.ietf-cdni-media-type] 884 Ma, K., "CDNI Media Type Registration", draft-ietf-cdni- 885 media-type-06 (work in progress), October 2015. 887 [I-D.ietf-cdni-metadata] 888 Niven-Jenkins, B., Murray, R., Caulfield, M., and K. Ma, 889 "CDN Interconnection Metadata", draft-ietf-cdni- 890 metadata-12 (work in progress), October 2015. 892 [RFC6707] Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content 893 Distribution Network Interconnection (CDNI) Problem 894 Statement", RFC 6707, DOI 10.17487/RFC6707, September 895 2012, . 897 [RFC6770] Bertrand, G., Ed., Stephan, E., Burbridge, T., Eardley, 898 P., Ma, K., and G. Watson, "Use Cases for Content Delivery 899 Network Interconnection", RFC 6770, DOI 10.17487/RFC6770, 900 November 2012, . 902 [RFC7336] Peterson, L., Davie, B., and R. van Brandenburg, Ed., 903 "Framework for Content Distribution Network 904 Interconnection (CDNI)", RFC 7336, DOI 10.17487/RFC7336, 905 August 2014, . 907 [RFC7337] Leung, K., Ed. and Y. Lee, Ed., "Content Distribution 908 Network Interconnection (CDNI) Requirements", RFC 7337, 909 DOI 10.17487/RFC7337, August 2014, 910 . 912 Appendix A. Acknowledgment 914 Jan Seedorf is partially supported by the GreenICN project (GreenICN: 915 Architecture and Applications of Green Information Centric 916 Networking), a research project supported jointly by the European 917 Commission under its 7th Framework Program (contract no. 608518) and 918 the National Institute of Information and Communications Technology 919 (NICT) in Japan (contract no. 167). The views and conclusions 920 contained herein are those of the authors and should not be 921 interpreted as necessarily representing the official policies or 922 endorsements, either expressed or implied, of the GreenICN project, 923 the European Commission, or NICT. 925 Martin Stiemerling provided initial input to this document and 926 valuable comments to the ongoing discussions among the authors of 927 this document. Thanks to Francois Le Faucheur and Scott Wainner for 928 providing valuable comments and suggestions to the text. 930 Authors' Addresses 932 Jan Seedorf 933 NEC 934 Kurfuerstenanlage 36 935 Heidelberg 69115 936 Germany 938 Phone: +49 6221 4342 221 939 Fax: +49 6221 4342 155 940 Email: seedorf@neclab.eu 942 Jon Peterson 943 NeuStar 944 1800 Sutter St Suite 570 945 Concord CA 94520 946 USA 948 Email: jon.peterson@neustar.biz 949 Stefano Previdi 950 Cisco Systems 951 Via Del Serafico 200 952 Rome 0144 953 Italy 955 Email: sprevidi@cisco.com 957 Ray van Brandenburg 958 TNO 959 Brassersplein 2 960 Delft 2612CT 961 The Netherlands 963 Phone: +31-88-866-7000 964 Email: ray.vanbrandenburg@tno.nl 966 Kevin J. Ma 967 Ericsson 968 43 Nagog Park 969 Acton, MA 01720 970 USA 972 Phone: +1 978-844-5100 973 Email: kevin.j.ma@ericsson.com