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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Service Function Chaining Guanwen Li 2 Internet Draft Guanglei Li 3 Intended status: Standards Track Taixin Li 4 Expires: April 12, 2018 Qi Xu 5 Bohao Feng 6 Huachun Zhou 7 Beijing Jiaotong University 8 October 11, 2017 10 Multi-domain Service Forwarding For NSH 11 draft-li-sfc-nsh-multi-domain-03 13 Status of this Memo 15 This Internet-Draft is submitted in full conformance with the 16 provisions of BCP 78 and BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet-Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html 33 This Internet-Draft will expire on October 19, 2017. 35 Copyright Notice 37 Copyright (c) 2017 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents carefully, 44 as they describe your rights and restrictions with respect to this 45 document. Code Components extracted from this document must include 46 Simplified BSD License text as described in Section 4.e of the Trust 47 Legal Provisions and are provided without warranty as described in 48 the Simplified BSD License. 50 Abstract 52 This document describes the mechanism to achieve multi-domain service 53 forwarding for NSH. The proposed mechanism adopts a horizontal 54 deployment structure, which divides a multi-domain SFC into several 55 segmental SFCs in the control plane and each domain creates its own 56 SFP independently in data plane. A label is proposed to identify 57 different cross-domain flows at the classifier by extending the 58 metadata of the NSH encapsulation. 60 Table of Contents 62 1. Introduction ................................................ 2 63 1.1. Requirement Language.................................... 3 64 2. Definition Of Terms ......................................... 4 65 3. Multi-domain Service Forwarding Mechanism ................... 3 66 3.1. Service Function Chaining Segmentation ................. 4 67 3.2. Inter-domain Service Forwarding ........................ 4 68 3.3. Classification and Intra-domain Service Forwarding...... 5 69 4. Multi-domain Service Forwarding Encapsulation ............... 5 70 5. Multi-domain Service Forwarding Example ..................... 6 71 6. Security Considerations...................................... 8 72 7. IANA Considerations ......................................... 8 73 8. Conclusions ................................................. 8 74 9. References .................................................. 8 75 9.1. Normative References.................................... 8 76 9.2. Informative References.................................. 9 77 10. Acknowledgments ............................................ 9 79 1. Introduction 81 Service Function Chaining (SFC) [RFC7665] is an architecture proposed 82 to decouple traditional network service functions with corresponding 83 physical resources. It is flexible and convenient for the network 84 operator to deploy on-demand service functions and steer the traffic 85 through them in sequence. 87 Network Service Header (NSH) [I-D.ietf-sfc-nsh] is defined as a data 88 plane protocol to create dynamic service function chains. According 89 to the NSH encapsulation, the flow can pass along pre-difined Service 90 Function Path and exchange metadata among the Service Classifier, the 91 Service Function and the Service Function Forwarder for information 92 sharing. 94 Network service forwarding in SFC is based on the combination of 95 Service Path Identifier (SPI) and Service index (SI), which are 96 defined in [I-D.ietf-sfc-nsh]. [I-D.kumar-sfc-nsh-forwarding] 97 analyzes the NSH forwarding shortcomings and further discusses the 98 separation of the service forwarding and the service delivery. 99 However, it focuses on infrastructure service forwarding for NSH in a 100 single domain. [I-D.ietf-sfc-hierarchical] proposes a hierarchical 101 way to achieve multi-domain forwarding for SFC, which can be regarded 102 as a vertical approach. Contrast to the vertical approach, a 103 horizontal one is easy to scale in and out. Besides, the horizontal 104 approach can decrease the overhead of the control plane, because it 105 maintains more service traffic in the data plane. 107 Therefore, this document proposes a horizontal approach to achieve 108 multi-domain service forwarding for NSH. The main idea is to divide a 109 multi-domain SFC into several segmental SFCs according to domain 110 partitions in the control plane and create corresponding SFPs in each 111 domain by its classifier independently. A label is proposed to 112 identify different cross-domain flows, which is encapsulated in the 113 metadata. 115 1.1. Requirement Language 117 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 118 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 119 document are to be interpreted as described in RFC 2119 [RFC2119]. 121 2. Multi-domain Service Forwarding Mechanism 123 +---------------------------------------------------+ 124 | | 125 | Control Plane | 126 | | 127 +-----+----------------+----------------------+-----+ 128 | | | 129 |Segmental |Segmental |Segmental 130 |SFC-1 |SFC-2 |SFC-N 131 | | | 132 +-----v-----+ +-----v-----+ +-----v-----+ 133 | | | | | | 134 ----> Domain1 +----> Domain2 +->......--> DomainN +---> 135 | | | | | | 136 +-----------+ +-----------+ +-----------+ 137 Figure 1 Multi-domain SFC Divide 139 As shown in Figure 1, according to requirements, it divides the whole 140 SFC in the control plane and issues cross-domain forwarding tables to 141 corresponding classifiers initially. Multi-domain service forwarding 142 includes two aspects: the inter-domain service forwarding and the 143 intra-domain service forwarding. The former is based on a unique 144 label for each flow, and the latter is performed by the classifier. 145 To achieve a unified service forwarding mechanism in multi-domain, 146 this mechanism uses metadata in NSH encapsulation to carry the 147 necessary forwarding information among different forwarding elements, 148 such as the Service Classifier and the Service Function Forwarder. 150 3. Definition Of Terms 152 This document uses some terms defined in SFC architecture [RFC7665] 153 and NSH [I-D.ietf-sfc-nsh] drafts for ease of understanding and the 154 reader is advised to refer to those documents for up to date and 155 additional information. 157 Segmental SFC: The cross-domain SFC is divided into several segmental 158 SFCs according to the domain partition. Each segmental SFC is 159 assigned to its corresponding domain. 161 Service Label: the label used to identify different flows can help 162 the classifier create the SFP by its corresponding segmental SFC, 163 which is issued from SFC control plane. 165 Cross-domain Forwarding Table: There are three columns in the table: 166 Service Label, Next Classifier and Segmental SFC. The table matches a 167 specific flow with its Service Label. The cross-domain forwarding of 168 the flow is depended on the address of Next Classifier. The Cross- 169 domain Forwarding Table is maintained by SFC control plane and issued 170 to corresponding classifier according to the Segmental SFC partition. 172 3.1. Service Function Chaining Segmentation 174 At first, the control plane creates a SFC with a unique Service Label 175 for the flow. Then, the SFC is divided into several segmental SFCs 176 according to physical resource constraints. It is important to note 177 that the control plane MUST NOT specific the SFP directly. The 178 control plane is only responsible to indicate what service functions 179 are required in each domain, and the corresponding SFP MUST be 180 specified by the service classifier. 182 3.2. Inter-domain Service Forwarding 184 The Service Label is proposed to identify different flows when 185 packets need to be cross-domain forwarded. When the service 186 classifier receives packets with NSH encapsulations, it checks the 187 Service Label of the first packet to look up the address of the next 188 classifier in its cross-domain forwarding table, which is issued by 189 SFC control plane. Then the information of next classifier is written 190 into the metadata and will be used by the last SFF in the Segmental 191 SFC. Once the last SFF receives the packet from last SF in the domain 192 which changes the SI to zero, it forwards the packets to next 193 classifier directly without any modification of their NSH 194 encapsulations. 196 The Service Label is only carried by the first packet of a certain 197 flow with specific SPI. It's beneficial to decrease header cost and 198 improve forwarding efficiency. 200 3.3. Classification and Intra-domain Service Forwarding 202 The service classifier creates SFP for each flow according to the 203 segmental SFC in its cross-domain forwarding table. After the control 204 plane assigns segmental SFCs for different domains, the corresponding 205 table is issued to the classifier in each domain. When the packet 206 arrives at the classifier, its Service Label is used to find out the 207 next segmental SFC. Then, the classifier creates a SFP for the flow 208 according to that segmental SFC. 210 In this situation, the classifier in a segmental SFC SHOULD set the 211 SI to the length of the segmental SFC. 213 4. Multi-domain Service Forwarding Encapsulation 215 In order to reduce overhead of metadata, the context header with MD 216 Type = 0x2 is chosen to support multi-domain service forwarding, 217 Figure 2 shows the allocation of the metadata. 219 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 221 |Ver|O|C|R|R|R|R|R|R| Length | MD-type=0x2 | Next Protocol | 222 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 223 | Service Path Identifier (SPI) | Service Index | 224 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 225 | Metadata Class=0x20 |C| Type=0x1 |R| Len=0x4 | 226 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 227 |D|R|R|R| Service Label | Next Classifier | 228 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 229 Figure 2 Multi-domain Service Forwarding Encapsulation 231 Context Header Allocation Descriptions: 233 Metadata Class: It MUST be set to 0x20 as requested in Section 7. 235 C bit: It SHOULD be set indicating critical metadata exists. 237 Type: It MUST be set to 0x1 for multi-domain service forwarding. 239 Len: Because the length of the context header is constant, it MUST be 240 set to 0x4. 242 D bit: The default value is zero, which means the metadata SHOULD be 243 ignored. When set to 0x1 indicates that this packet need to be for- 244 warded in multiple domains. 246 Service Label: Identifies different flows with different labels. The 247 service classifier decides the service forwarding path of the packet 248 according to its domain label with a forwarding table issued by 249 control plane. 251 Next Classifier: Indicates the identifier of the classifier in next 252 domain. Because of the SFC segmentation, each classifier only works 253 in the SFC domain it belongs to. When the current segmental SFC is 254 terminate, the last SFF will query the next segmental domain by this 255 identifier. 257 All other flag fields are reserved for future use. Reserved bits MUST 258 be set to zero and MUST be ignored upon receipt. 260 5. Multi-domain Service Forwarding Example 262 +----------+ +----------+ +----------+ 263 | | | | | | 264 Domain1 | SF-a | | SF-b | Domain2 | SF-c | 265 | | | | | | 266 +---^--+---+ +---^--+---+ +---^--+---+ 267 | | | | | | 268 +-------+ +---+--v---+ +---+--v---+ +-------+ +---+--v---+ 269 | | | | | | | | | | 270 ---> CF1 +-> SFF1-1 +-> SFF1-2 +----> CF2 +-> SFF2-1 +---> 271 | | | | | | | | | | 272 +-------+ +----------+ +----------+ +-------+ +----------+ 273 Figure 3 Multi-domain Service Forwarding Example 275 This section describes the scenario shown in Figure 3, a packet flow 276 pass through three service functions deployed in two domains. The 277 Domain1 is consist of CF1, SFF1-1, SFF1-2, SF-a and SF-b; the Domain2 278 is consist of CF2, SFF2-1 and SF-c. The workflow is as follow: 280 1.SFC control plane creates the SFC with a Service Label for the 281 specific flow and divides the whole SFC into several segmental SFCs. 283 2.The cross-domain forwarding table is issued to its corresponding 284 classifier with specific Service Label, Next Classifier and Segmental 285 SFC. 287 3.CF1(the classifier in domain1) creates the SFP and the NSH 288 encapsulation for the first packet of a certain flow according to its 289 segmental SFC in domain1. It sets 'D' flag to 1 and fills in the 290 Service Label and Next Classifier. The SI is set to the length of 291 this segmental SFC. 293 4.CF1 forwards the packet to SFF1-1. 295 5.SFF1-1 determines SF-a as the next hop and forwards the packet. 297 6.After SF-a processes the packet, the packet is forwarded back to 298 SFF with decremented SI. 300 7.SFF1-1 forwards the received packet to SFF1-2. 302 8.SFF1-2 determines SF-a as the next hop and forwards the packet. 304 9.Similar to SF-a, SF-b forwards the packet to SFF1-2 and decrements 305 SI to zero. 307 10.When SFF1-2 receives the packet, it finds out that the segmental 308 SFC is terminate in this domain because of the SI, and then SFF1-2 309 forwards the packet to next classifier without modification of the 310 NSH encapsulation. The following packets of this flow (in same SPI in 311 this domain) are forwarded with the same routing information. 313 11.When CF2(the classifier in domain2) receives the first packet with 314 an NSH encapsulation, CF2 will checks its Service Label. 316 12.Accroding to the Service Label, CF2 looks up segmental SFC in the 317 cross-domain forwarding table and creates the corresponding SFP and 318 the NSH encapsulation. 320 13.CF2 sets the 'D' flag to zero and forwards the packet to SFF2-1. 321 The action of its following packets are similar. 323 13.SFF2-1 determines SF-c as the next hop and forwards the packet. 325 14.SFc processes the packet and forwards it back to SFF2-1 with 326 decremented SI. 328 15.SFF2-1 finds out that the SFP is terminate and forwards the packet 329 to the final Receiver. 331 6. Security Considerations 333 As with many other protocols, metadata of the NSH encapsulation can 334 be spoofed or otherwise modified. It is important to protect the 335 cross-domain packet from malicious modification, because the metadata 336 contains sensitive information about the user and environment. 337 Therefore, it is significate to ensure the integrity of the metadata 338 and provide the protection of the user privacy. 340 7. IANA Considerations 342 IANA is requested to allocate a new class from the TLV Class defined 343 in [I-D.ietf-sfc-nsh]. 345 0x20 Multi-domain Forwarding Type 347 IANA is requested to set up a registry of "NSH Multi-domain Service 348 Forwarding TLV Types". These are 7-bit values. Registry entries 349 are assigned by using the "IETF Review" policy defined in [RFC5226]. 351 IANA is requested to allocate two new types as follows: 353 o Type = 0x00 Reserved 355 o Type = 0x01 Multi-domain Service Forwarding 357 8. Conclusions 359 This document proposes a mechanism for multi-domain service forward- 360 ing based on a unique label. In order to relieve the pressure of the 361 control plane, the multi-domain SFC is divided into segmental SFC 362 according to the domain partitions, and the SFP in each domain is 363 created independently. 365 9. References 367 9.1. Normative References 369 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 370 Requirement Levels", BCP 14, RFC 2119, March 1997. 372 [I-D.ietf-sfc-nsh] 373 Quinn, P. and U. Elzur, "Network Service Header", draft- 374 ietf-sfc-nsh-26 (work in progress), October 2017. 376 9.2. Informative References 378 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 379 IANA Considerations Section in RFCs", BCP 26, RFC 8126, 380 June 2017. 382 [RFC7665] J. Halpern, Ed. and C. Pignataro, Ed. "Service Function 383 Chaining (SFC) Architecture", October 2015. 385 [I-D.ietf-sfc-hierarchical] 387 D. Dolson, S. Homma, D. Lopez, et al. "Hierarchical Service 388 Function Chaining", draft-ietf-sfc-hierarchical-02 (work in 389 progress), January 2017. 391 [I-D.kumar-sfc-nsh-forwarding] 393 S. Kumar, K. Leung, P. Bosch, et al. "Infrastructure 394 Service Forwarding For NSH", draft-kumar-sfc-nsh- 395 forwarding-01, August 2016. 397 10. Acknowledgments 399 This work in this document was supported by National High Technology 400 of China ("863 program") under Grant No.2015AA015702. 402 Authors' Addresses 404 Guanwen Li 405 Beijing Jiaotong University 406 Beijing 100044, P.R. China 408 Email: 14120079@bjtu.edu.cn 410 Guanglei Li 411 Beijing Jiaotong University 412 Beijing 100044, P.R. China 414 Email: 15111035@bjtu.edu.cn 416 Taixin Li 417 Beijing Jiaotong University 418 Beijing 100044, P.R. China 420 Email: 14111040@bjtu.edu.cn 422 Qi Xu 423 Beijing Jiaotong University 424 Beijing 100044, P.R. China 426 Email: 15111046@bjtu.edu.cn 428 Bohao Feng 429 Beijing Jiaotong University 430 Beijing 100044, P.R. China 432 Email: bohaofeng@bjtu.edu.cn 434 Huachun Zhou 435 Beijing Jiaotong University 436 Beijing 100044, P.R. China 438 Email: hchzhou@bjtu.edu.cn