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Kim 5 Expires: 30 October 2022 Soongsil University 6 28 April 2022 8 LISP Support for Dynamic Anycast Routing 9 draft-kjsun-lisp-dyncast-02 11 Abstract 13 Dynamic Anycast (Dyncast) is a new routing approach to support 14 equivalent services running in distributed geolocations and connect 15 to them by considering both network-related metric and service- 16 related metric. In LISP, it is possible to support anycast EIDs and/ 17 or anycast RLOCs without any modification, so it is suitable for 18 providing dyncast routing. In this document, it describes the LISP- 19 based dyncast architecture and related standard works to meet dyncast 20 requirements. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at https://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on 30 October 2022. 39 Copyright Notice 41 Copyright (c) 2022 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 46 license-info) in effect on the date of publication of this document. 47 Please review these documents carefully, as they describe your rights 48 and restrictions with respect to this document. Code Components 49 extracted from this document must include Revised BSD License text as 50 described in Section 4.e of the Trust Legal Provisions and are 51 provided without warranty as described in the Revised BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 3. Architecture Overview . . . . . . . . . . . . . . . . . . . . 3 58 4. Addressing Dyncast Requirements with LISP . . . . . . . . . . 6 59 4.1. Anycast-based Service Addressing . . . . . . . . . . . . 6 60 4.2. Instance Affinity . . . . . . . . . . . . . . . . . . . . 7 61 4.3. Encoding and Signaling of Metric . . . . . . . . . . . . 8 62 4.4. Dynamic Routing Decisions based using Metrics . . . . . . 9 63 4.5. Supporting Service Dynamism . . . . . . . . . . . . . . . 10 64 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 65 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 66 6.1. Informative References . . . . . . . . . . . . . . . . . 10 67 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 69 1. Introduction 71 With emerging that multiple edge sites deployed at different 72 locations and had different capacity to provide a service with edge 73 computing, when the clients requests service, there is a requirement 74 to make "best" decision to select edge node among requested service 75 running simultaneously on multiple edges. While distributing service 76 requests to a specific service having multiple instances attached to 77 multiple edges, one of solution is to take into account computing as 78 well as service-specific metrics in the distribution decision seen as 79 dynamic anycast ("dyncast", for short). 81 The main feature of the dyncast described in 82 [draft-liu-dyncast-ps-usecases] is that a unique service identifier 83 that can be assigned to multiple instances in multiple edge 84 environments should be able to be mapped as an actual routable 85 unicast address. Since this concept is similar to the Location/ID 86 separation method already used in the LISP design basis, the LISP 87 protocol can be considered as one of the candidate protocols that can 88 implement dyncast. This draft is proposed to design the LISP-based 89 architecture for Dyncast and analyze the extension method of LISP to 90 meet the requirements defined in [draft-liu-dyncast-reqs] for 91 realizing dynamic anycasting between different LISP sites. 93 2. Terminology 95 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 96 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 97 document is to be interpreted as described in [RFC2119]. This 98 document uses the terminology described in [RFC6830], 99 [draft-liu-dyncast-ps-usecases], [draft-liu-dyncast-reqs]. Detailed 100 definition of terminologies are written below. 102 Dyncast : As defined in [draft-liu-dyncast-ps-usecases], Dynamic 103 Anycast, taking the dynamic nature of computing resource metrics into 104 account to steer an anycast routing decision. 106 D-Router: A node supporting Dyncast functionalities as described in 107 this document. Namely it is able to understand both network-related 108 and service-instances-related metrics, take forwarding decision based 109 upon and manitain instance affinity, i.e., forwards packets belonging 110 to the same service demand to the same instance. 112 Dyncast Metric Agent (D-MA): A dyncast specific agent able to gather 113 and send metric updates (from both network and instance prespective) 114 but not performing forwarding decisions. May run on a D-Router, but 115 it can be also implementated as a separate module (e.g., a software 116 library) collocated with a service instance. 118 Dyncast Service Endpoint ID (DSEID) : Anycast IP address assigned to 119 the service running on distributed locations. DSEID cannot be routed 120 globally, and it is unique for specific service. Multiple service 121 instances which are same service have a same DSEID. 123 D-BID: Dyncast Binding D-Node, an address to reach a service instance 124 for a given DSEID. It is usually a unicast IP where service 125 instances are attached. Different service instances provide the same 126 service identified through D-SID but with different Dyncast Binding 127 IDs. In the LISP architecture, D-BIDs of same service are replaced 128 to RLOC-set of DSEID. 130 3. Architecture Overview 132 Figure 1 describes the LISP use-case for dynamic anycast. In the 133 LISP architecture [draft-ietf-lisp-introduction-13], each edge 134 network has one or more LISP routers deployed. For anycast address, 135 [RFC6830] defines that anycast address can be assigned for both 136 Endpoint ID (EID) and Routing Locator (RLOC) within each of their 137 address spaces. In this draft, we called EID for dynamic anycasting 138 as Dyncast Service Endpoint ID (DSEID), which is assigned to 139 equivalent services across the multiple LISP sites. Similar to the 140 common EID definition, the DSEID cannot be routed globally by itself, 141 and the same DSEID cannot be assigned to different services. In 142 order to forward a packet destined for a DSEID between LISP edges, 143 the addresses of the LISP Egress Tunnel Router (ETR) are used as 144 RLOC-set, which was difined as a Dyncast Binding ID (D-BID) in 145 [draft-li-dyncast-architecture]. Unlike D-BID which is routable and 146 unique for all each service instance, RLOC-set is routable in the 147 underlay but it is not unique values per each service instances. 148 When multiple services are running in the same LISP site, they can be 149 assigned the same RLOC which is xTR of their LISP site. Map-server/ 150 resolver of the LISP control plane can manage mapping information for 151 DESID-to-RLOC-set mappings together with existing EID-to-RLOC 152 mappings. 154 For resource-efficient forwarding decisions across multiple service 155 instances, [draft-li-dyncast-architecture] defines Dyncast Metric 156 Agent (D-MA) which collects metrics related network and service 157 instances. Actual packet forwarding is handled in the Dyncast Router 158 (D-Router) based upon collected metrics with maintaining instance 159 affinity. In the LISP architecture, the D-Router and D-MA function 160 can be implemented on each LISP ETR, or can be deployed as separate 161 components within the edge for managing service instances. The LISP 162 control plane is logically centralized and it provides an interface 163 with each LISP router to exchange mapping information. However, it 164 does not mean that the LISP control plane is located in a single 165 physical location, several mechanisms for distributing the mapping 166 system already have been defined. 168 +------------------+ 169 |LISP Control Plane| 170 +------------------+ 171 | +--------+ +--------+ 172 | ___|LISP-ETR|---|Service1| DESID 173 ......... / +--------+ +--------+ 174 .. .. 175 +------+ +--------+ : Core : +--------+ +--------+ 176 |Client|--|LISP ITR|-: Network :---|LISP-ETR|---|Service1| DESID 177 +------+ +--------+ :(RLOC-space) : +--------+ +--------+ 178 EID .. .. 179 ......... \ +--------+ +--------+ 180 \__|LISP-ETR|---|Service1| DESID 181 +--------+ +--------+ 183 Figure 1: LISP use-case for Dynamic anycast 185 Figure 3 shows an example of LISP-based dyncast deployment where two 186 services each deployed two instances at different edges. In this 187 scenario, two services are assigned an RLOC according to the ETR 188 address of the LISP site. Both Service_A and Service_B instances 189 connected to ETR_2 are assigned RLOC2, which is the RLOC of ETR_2, as 190 a binding ID. According this figure, DSEID-to-RLOC-set mappings can 191 be configured as an example below. 193 DSEID RLOC-set 194 ----------------------------------------------------------- 195 DSEID_A RLOC-set_A ({RLOC2, metric}, {RLOC3, metric}) 196 DSEID_B RLOC-set_B ({RLOC2, metric}, {RLOC3, metric}) 198 Figure 2: DSEID-to-RLOC-set Example 200 In addition to these examples, the RLOC-set can also be used in the 201 form of Explicit Locator Path (ELP) or Run-Length Encoding (RLE) for 202 the encap-path between ETR and ITR. 204 In the case of the edge where ETR_2 is located, as an edge composed 205 only of service instances, the LISP Router function can be operated 206 by being strongly coupled to the edge computing server. In this 207 case, the D-MA function can be implemented on the ETR to insert 208 service-instance-related metrics directly into the LISP protocol 209 packet. In case that a service instance and a client co-exist like 210 an edge where ETR_3 is located, the D-MA entity can be independently 211 deployed proximity of the service instance is running, transparent 212 from the LISP operation for clients. Mapping information update for 213 DSEID is performed through the LISP protocol Map-Register message, 214 and service-instance-related metric can be delivered through in the 215 LISP protocol header or other methods. A method of inserting 216 service-instance-related metric information into the LISP protocol 217 will be discussed later. When the ITR_1 receives a packet destined 218 for the DSEID of the service by service request from the Host_1, the 219 ITR can acquire the RLOC-set of the requested DSEID from the LISP 220 control-plane through the Map-Request message. At the control plane, 221 it may select a proper RLOC on the collected metric information and 222 return it to the ITR or return the RLOC-set of multiple service 223 instances with metric information to the ITR so the ITR selects the 224 proper RLOC in the set. A method for determining an appropriate RLOC 225 will be discussed later. 227 Service_A 228 +-------+ 229 Map-Register D-Router +-|DSEID_A| 230 (DSEID_A, RLOC2, ) +-------+------+ | +-------+ 231 (DESID_B, RLOC2, ,metric>) | ETR_2 | D-MA |-| 232 +-------+------+ | +-------+ 233 | +-|DSEID_B| 234 +------------------+ | RLOC2 +-------+ 235 Host_1 D-Router | +--------------+ |--+ Service_B 236 +--------+ +-------+ | | LISP | | 237 | EID_H1 |--| ITR_1 |----| | Control Plane| | Map-Register 238 +--------+ +-------+ | +--------------+ |(DSEID_A, RLOC3, ) 239 RLOC1| RLOC-Space |(DSEID_B, RLOC3, ) 240 | |--+ RLOC3 241 <---- +------------------+ | 242 Map-Reply D-Router Host_2 243 (DSEID_A, RLOC-set_A, ) +-------+ +--------+ 244 (DSEID_B, RLOC-set_B, ) | ETR_3 |---| EID_H2 | 245 +-------+ +--------+ 246 | 247 +------+ 248 | D-MA | 249 +------+ 250 | 251 +-----+-----+ 252 | | 253 +-------+ +-------+ 254 |DSEID_A| |DSEID_B| 255 +-------+ +-------+ 256 Service_A Service_B 258 Figure 3: LISP-based Dyncast Example Scenario 260 4. Addressing Dyncast Requirements with LISP 262 4.1. Anycast-based Service Addressing 264 To support dyncast routing, the system must provide a method for 265 searching a service identifier allocated as an anycast address and 266 mapping it to a specific unicast address. From this point of view, 267 the LISP is a suitable protocol for separating ID/Location of service 268 and managing mapping information. When the system allocates the same 269 DSEID to each service instance for service equivalency, the LISP can 270 define an anycast address space for the DSEID and assign it to 271 service instances created across multiple sites. Also, the D-BID can 272 be replaced to an RLOC address of LISP xTR that can be routed between 273 edges as unicast. That is, it is necessary to define a separate 274 space for anycast address within the existing EID space and to 275 allocate it in advance so that it can be used in all edge networks 276 where the service instances are located. In the LISP definition, the 277 EID assigned to each service has a globally unique value and, in 278 particular, [RFC6830] defines that anycast address can be assigned 279 within an EID or RLOC block spaces. In each LISP site, same as the 280 EID which is defined to enable internal routing, the DSEID can be 281 able to be routed without the RLOC encapsulation process to the EID 282 within a single site. 284 One of alternative addressing solution is to use anycast-SEID-to- 285 anycast-RLOC mapping. Using this, it is required to register from 286 one place (an SDN controller) or each ETR registering the same RLOC 287 without any merge semantics. So the service is chosen by destination 288 address in a packet (the anycast-EID) which maps to an anycast-RLOC 289 where the underlay takes you to the "closest" LISP site. However, in 290 the dyncast, routing selection is not depending on just distance but 291 also computing resources of each service location. Depending on 292 dynamics of these metrics, anycast-RLOC should be registered/ 293 deregistered at the ETR depending on the absence of specific anycast- 294 EID. Further discussion is required which is more efficient rather 295 than using indirection mapping and update it with unicast-RLOC with 296 metric information. 298 4.2. Instance Affinity 300 For dyncast routing, it is required that the system must set 301 "Instance Affinity" for one or several service requests to provide 302 routing to the same service instance for the same flow. In LISP, the 303 RLOC mapping information for the destination EID is stored in a local 304 cache called Map-cache in the ITR for a certain period of time, and 305 it is maintained for a set time-to-live (TTL) time. Therefore, 306 mapping information for a specific service once requested from a 307 client is generally maintained in the ITR until the corresponding 308 session expires and can be delivered to the RLOC stored in the map- 309 cache entry. However, in order to have a flexible selection of 310 service instances between different flows at the same point, it is 311 additionally required to assign different RLOCs for different flows 312 depending on metrics dynamically changed. For that, it is necessary 313 to enhance ITR Map-cache to maintain destination RLOC for each flow. 314 In [draft-rodrigueznatal-lisp-multi-tuple-eids], it can be supported 315 to store Multi-Tuple Extend-EID mappings. With Multi-Tuple EID 316 mappings, it is possible to provide RLOC affinity depending on its 317 destination DSEID as well as other information such as source EID, 318 protocol or port number. For that, it is required to support multi- 319 stage lookup process, where the multi-tuple EID mappings that point 320 to an DSEID and then there is a DSEID mapping that points to RLOC- 321 set. 323 In addition, although the general TTL value in LISP ITR is defined as 324 24 hours, in dyncast the system requires a shorter TTL time for 325 changing network path depending on dynamically updated network- 326 related and service-instance-related metrics. The LISP support to 327 send a refresh Map-Request before removing map-cache entry. If it 328 needs a shorter TTL to update the map-cache, two options are 329 possible. First option is to send Solicit Map-Request(SMR) for 330 refreshing cache, and another option is to use Pub/Sub which is 331 described in [draft-ietf-lisp-pubsub]. 333 4.3. Encoding and Signaling of Metric 335 In dyncast routing, the one of most important requirements is that it 336 should be able to collect various metrics of service-instances- 337 related as well as network-related, and include them in-network 338 routing decisions. For that, it is necessary to define how to 339 collect these metrics and forward them, and also where to make a 340 decision. In the LISP environment, since that the entire EID-RLOC 341 mapping information is managed in the control plane, one possible 342 scenario is that the D-MA function which collects service-instance- 343 related metrics updates them to the DSEID mapping entry in the LISP 344 control plane. For that, it can be used an encoding method proposed 345 in [draft-farinacci-lisp-name-encoding] that defines to insert 346 specific information such as parameters for a specific EID or RLOC 347 using an ASCII string. Using that, it is possible to encode a string 348 that is pre-defined of a specific metric to interpret in the control 349 plane and send a Map-Request message so that the control plane can 350 select an appropriate RLOC based on it. Another possible option is 351 to use policy distribution by a network controller, which is proposed 352 in [draft-kowal-lisp-policy-distribution]. Using network controller, 353 the ITR could receive and apply the QoS policies that would shape 354 traffic to the correct rate on each ITR RLOC interface. In order to 355 insert service-instance-related metrics from the DSEID side, the D-MA 356 must forward the metrics of the requested service to the LISP ITR so 357 that the metric can be inserted into the header of the Map-Register 358 message. This metric information encoded into the Map-Register 359 message can help the LISP control plane to make multi-tuple mapping 360 entry and sent it to the requested ITR. Once the requested ITR 361 receives these information, it can make a routing decision based on 362 the multi-tuple parameters. 364 4.4. Dynamic Routing Decisions based using Metrics 366 The dyncast system is required that in must make routing decisions 367 for all service requests, and this must be done under an 368 understanding of all metrics. Routing decisions in the LISP can be 369 done with two options which is done in the control plane or ITR by 370 specifying priority and weight values for each RLOC. In case that 371 routing decisions are made in the control plane, the Map-Resolver 372 dynamically sets the priority and weight values of each mapped RLOCs 373 collected from D-MAs, selects a proper RLOC based on them, and 374 forward it to the requested ITR using the Map-Reply message. 375 However, since this centralized approach may not be calculated based 376 on point of requested ITR, the actual routing path may not be 377 optimal. In case that routing decision is determined at the ITR, the 378 LISP control plane may return one or more RLOC values for the 379 requested DSEID to the ITR, including priority and weight values 380 based on the collected metrics. After receiving multiple DBIDs, the 381 ITR stores them in map-cache entry and selects an appropriate one to 382 forward the data packet. For that, a mechanism for estimating 383 appropriate priority and weight values based on both network-related 384 and service-instance-related metrics is required for the control 385 plane or ITR. When DSEID-to-RLOC-set mapping is used, it is noted 386 that if RLOCs in the set have equal priority, the ITR can load-split 387 traffic across RLOCs and that cause to break session connection. So, 388 an ITR that is configured that a particular EID in its map-cache is 389 an DSEID, it should be cared to use an RLOC-set above with each RLOC 390 priority=1. 392 In the dyncast architecture described in 393 [draft-li-dyncast-architecture], the D-Router collects metrics by 394 exchanging metric information of the service identifier between 395 another edge D-Routers and make a decision itself. This approach can 396 minimize the signaling for routing decisions by decentralizing the 397 authority for the anycast routing decision to an entity in the actual 398 packet path, but the signaling for collecting metrics between each 399 D-Router is bound to increase. In contrast, when the LISP is used, 400 it can reduce effectively signaling of collecting metrics from the 401 ITR since that the mapping information for DSEID and RLOC-set can be 402 managed in a centralized control plane. However, if the metrics 403 change too much then the contents of the RLOC-set changes which 404 requires more frequent map-cache updates. So analyzing in depth of 405 this tradeoff remains further studies. 407 4.5. Supporting Service Dynamism 409 For service dynamism, the dyncast system should support different 410 selections for each flow according to a dynamically changing metric 411 while considering various requirements in the selection of a service 412 instance. As mentioned in Section 4.2, 413 [draft-rodrigueznatal-lisp-multi-tuple-eids] can provide the map- 414 cache to be maintained for each flow, so the forwarding path can be 415 dynamically changed to the different service instances by allocating 416 target RLOC to the map-cache entry per-flow according to dynamic 417 changes of metrics. In order to refresh the DSEID-to-RLOC-set 418 mapping upon changing metric, the Solicit Map-Request(SMR) message 419 can be used to update so that the ITR can update the weight and 420 priority for the RLOC which is already received from the Map-server. 421 Additionally, as proposed in [draft-farinacci-lisp-telemetry], 422 telemetry data can be collected between Encapsulating/Decapsulating 423 xTRs of the current flow, which is expected to be used for dynamic 424 service path reselection. 426 5. Security Considerations 428 TBD 430 6. References 432 6.1. Informative References 434 [draft-farinacci-lisp-name-encoding] 435 Farinacci, D., "LISP Distinguished Name Encoding", May 436 2021, . 439 [draft-farinacci-lisp-telemetry] 440 Farinacci, D., Ouissal, S., and E. Nordmark, "LISP Data- 441 Plane Telemetry", May 2021, 442 . 445 [draft-ietf-lisp-introduction-13] 446 Cabellos, A. and D. Saucez, "An Architectural Introduction 447 to the Locator/ID Separation Protocol (LISP)", April 2015, 448 . 451 [draft-ietf-lisp-pubsub] 452 Rodrigues-Natal, A., Ermagan, V., Cabellos, A., Barkai, 453 S., and M. Boucadair, "Publish/Subscribe Functionality for 454 LISP", June 2021, . 457 [draft-kowal-lisp-policy-distribution] 458 Kowal, M., Portoles, M., Jain, A., and D. Farinacci, "LISP 459 Transport for Policy Distribution", September 2021, 460 . 463 [draft-li-dyncast-architecture] 464 Li, Y., Iannone, L., Trossen, D., and P. Liu, "Dynamic- 465 Anycast Architecture", February 2021, 466 . 469 [draft-liu-dyncast-ps-usecases] 470 Liu, P., Willis, P., and D. Trossen, "Dynamic-Anycast 471 (Dyncast) Use Cases; Problem Statement", February 2021, 472 . 475 [draft-liu-dyncast-reqs] 476 Liu, P., Willis, P., and D. Trossen, "Dynamic-Anycast 477 (Dyncast) Requirements", February 2021, 478 . 481 [draft-rodrigueznatal-lisp-multi-tuple-eids] 482 Rodrigues-Natal, A., Cabellos-Aparicio, A., Barkai, S., 483 Ermagan, V., Lewis, D., Maino, F., and D. Farinacci, "LISP 484 support for Multi-Tuple EIDs", October 2021, 485 . 488 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 489 Requirement Levels", RFC 2119, March 1997, 490 . 492 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 493 Locator/ID Separation Protocol (LISP)", RFC 6830, January 494 2013, . 496 Authors' Addresses 497 Kyoungjae Sun 498 ETRI 499 218, Gajeong-ro, Yuseung-gu 500 Dajeon 501 34065 502 Republic of Korea 503 Phone: +82 10 3643 5627 504 Email: kjsun@etri.re.kr 506 Younghan Kim 507 Soongsil University 508 369, Sangdo-ro, Dongjak-gu 509 Seoul 510 06978 511 Republic of Korea 512 Phone: +82 10 2691 0904 513 Email: younghak@ssu.ac.kr