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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (April 15, 2014) is 3654 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- No issues found here. Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group P. Quinn, Ed. 3 Internet-Draft Cisco Systems, Inc. 4 Intended status: Informational T. Nadeau, Ed. 5 Expires: October 17, 2014 Brocade 6 April 15, 2014 8 Service Function Chaining Problem Statement 9 draft-ietf-sfc-problem-statement-04.txt 11 Abstract 13 This document provides an overview of the issues associated with the 14 deployment of service functions (such as firewalls, load balancers) 15 in large-scale environments. The term service function chaining is 16 used to describe the definition and instantiation of an ordered set 17 of instances of such service functions, and the subsequent "steering" 18 of traffic flows through those service functions. 20 The set of enabled service function chains reflect operator service 21 offerings and is designed in conjunction with application delivery 22 and service and network policy. 24 Status of this Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at http://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on October 17, 2014. 41 Copyright Notice 43 Copyright (c) 2014 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 1.1. Definition of Terms . . . . . . . . . . . . . . . . . . . 3 60 2. Problem Space . . . . . . . . . . . . . . . . . . . . . . . . 5 61 2.1. Topological Dependencies . . . . . . . . . . . . . . . . . 5 62 2.2. Configuration complexity . . . . . . . . . . . . . . . . . 5 63 2.3. Constrained High Availability . . . . . . . . . . . . . . 6 64 2.4. Consistent Ordering of Service Functions . . . . . . . . . 6 65 2.5. Application of Service Policy . . . . . . . . . . . . . . 6 66 2.6. Transport Dependence . . . . . . . . . . . . . . . . . . . 7 67 2.7. Elastic Service Delivery . . . . . . . . . . . . . . . . . 7 68 2.8. Traffic Selection Criteria . . . . . . . . . . . . . . . . 7 69 2.9. Limited End-to-End Service Visibility . . . . . . . . . . 7 70 2.10. Per-Service (re)Classification . . . . . . . . . . . . . . 7 71 2.11. Symmetric Traffic Flows . . . . . . . . . . . . . . . . . 8 72 2.12. Multi-vendor Service Functions . . . . . . . . . . . . . . 8 73 3. Service Function Chaining . . . . . . . . . . . . . . . . . . 9 74 3.1. Service Overlay . . . . . . . . . . . . . . . . . . . . . 9 75 3.2. Control Plane . . . . . . . . . . . . . . . . . . . . . . 9 76 3.3. Service Classification . . . . . . . . . . . . . . . . . . 9 77 3.4. Dataplane Metadata . . . . . . . . . . . . . . . . . . . . 10 78 4. Related IETF Work . . . . . . . . . . . . . . . . . . . . . . 11 79 5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 80 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 81 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 14 82 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 83 9. Informative References . . . . . . . . . . . . . . . . . . . . 17 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 86 1. Introduction 88 The delivery of end-to-end services often require various service 89 functions including traditional network service functions (for 90 example firewalls and server load balancers), as well as application- 91 specific features. Service functions may be delivered within the 92 context of an isolated user group, or shared amongst many users/user 93 groups 95 Current service function deployment models are relatively static in 96 that they are tightly coupled to network topology and physical 97 resources. The result of that static nature of existing deployments 98 greatly reduces, and in many cases, limits the ability of an operator 99 to introduce new services and/or service functions. Furthermore 100 there is a cascading effect: service changes affect other services. 102 This document outlines the problems encountered with existing service 103 deployment models for Service Function Chaining (SFC) (often referred 104 to simply as service chaining; in this document the terms will be 105 used interchangeably), as well as the problems of service chain 106 creation/ deletion, policy integration with service chains, and 107 policy enforcement within the network infrastructure. 109 1.1. Definition of Terms 111 Classification: Locally instantiated policy that results in matching 112 of traffic flows for identification of appropriate outbound 113 forwarding actions. 115 Network Overlay: A logical network built, via virtual links or 116 packet encapsulation, over an existing network (the underlay). 118 Network Service: An externally visible service offered by a network 119 operator; a service may consist of a single service function or a 120 composite built from several service functions executed in one or 121 more pre-determined sequences and delivered by one or more service 122 nodes. 124 Service Function: A function that is responsible for specific 125 treatment of received packets. A Service Function can act at the 126 network layer or other OSI layers. A Service Function can be a 127 virtual instance or be embedded in a physical network element. 128 One of multiple Service Functions can be embedded in the same 129 network element. Multiple instances of the Service Function can 130 be enabled in the same administrative domain. 132 A non-exhaustive list of Service Functions includes: firewalls, 133 WAN and application acceleration, Deep Packet Inspection (DPI), 134 server load balancers, NAT44 [RFC3022], NAT64 [RFC6146], HOST_ID 135 injection [RFC6967], HTTP Header Enrichment functions, TCP 136 optimizer, etc. 138 The generic term "L4-L7 services" is often used to describe many 139 service functions. 141 Service Function Chain (SFC): A service Function chain defines an 142 ordered set of service functions that must be applied to packets 143 and/or layer-2 frames selected as a result of classification. The 144 implied order may not be a linear progression as nodes may copy to 145 more than one branch. The term service chain is often used as 146 shorthand for service function chain. 148 Service Function Path (SFP): The instantiation of a service function 149 chain in the network. Packets follow a service function path from 150 a classifier through the required instances of service functions 151 in the network. 153 Service Node (SN): Physical or virtual element that hosts one or 154 more service functions. 156 Service Overlay: An overlay network created for the purpose of 157 forwarding data along a service function path. 159 Service Topology: The service overlay connectivity forms a service 160 topology. 162 2. Problem Space 164 The following points describe aspects of existing service deployments 165 that are problematic, and that the Service Function Chaining (SFC) 166 working group aims to address. 168 2.1. Topological Dependencies 170 Network service deployments are often coupled to network topology, 171 whether it be real or virtualized, or a hybrid of the two. Such 172 dependency imposes constraints on the service delivery, potentially 173 inhibiting the network operator from optimally utilizing service 174 resources, and reduces the flexibility. This limits scale, capacity, 175 and redundancy across network resources. 177 These topologies serve only to "insert" the service function (i.e., 178 ensure that traffic traverses a service function); they are not 179 required from a native packet delivery perspective. For example, 180 firewalls often require an "in" and "out" layer-2 segment and adding 181 a new firewall requires changing the topology (i.e., adding new 182 layer-2 segments). 184 As more service functions are required - often with strict ordering - 185 topology changes are needed before and after each service function 186 resulting in complex network changes and device configuration. In 187 such topologies, all traffic, whether a service function needs to be 188 applied or not, often passes through the same strict order. 190 The topological coupling limits placement and selection of service 191 functions: service functions are "fixed" in place by topology and 192 therefore placement and service function selection taking into 193 account network topology information is not viable. Furthermore, 194 altering the services traversed, or their order, based on flow 195 direction is not possible. 197 A common example is web servers using a server load balancer as the 198 default gateway. When the web service responds to non-load balanced 199 traffic (e.g., administrative or backup operations) all traffic from 200 the server must traverse the load balancer forcing network 201 administrators to create complex routing schemes or create additional 202 interfaces to provide an alternate topology. 204 2.2. Configuration complexity 206 A direct consequence of topological dependencies is the complexity of 207 the entire configuration, specifically in deploying service function 208 chains. Simple actions such as changing the order of the service 209 functions in a service function chain require changes to the 210 topology. Changes to the topology are avoided by the network 211 operator once installed, configured and deployed in production 212 environments fearing misconfiguration and downtime. All of this 213 leads to very static service delivery deployments. Furthermore, the 214 speed at which these topological changes can be made is not rapid or 215 dynamic enough as it often requires manual intervention, or use of 216 slow provisioning systems. 218 2.3. Constrained High Availability 220 An effect of topological dependency is constrained service function 221 high availability. Worse, when modified, inadvertent non-high 222 availability or downtime can result. 224 Since traffic reaches many service functions based on network 225 topology, alternate, or redundant service functions must be placed in 226 the same topology as the primary service. 228 2.4. Consistent Ordering of Service Functions 230 Service functions are typically independent; service function_1 231 (SF1)...service function_n (SFn) are unrelated and there is no notion 232 at the service layer that SF1 occurs before SF2. However, to an 233 administrator many service functions have a strict ordering that must 234 be in place, yet the administrator has no consistent way to impose 235 and verify the ordering of the service functions that are used to 236 deliver a given service. 238 Service function chains today are most typically built through manual 239 configuration processes. These are slow and error prone. With the 240 advent of newer service deployment models the control and policy 241 planes provide not only connectivity state, but will also be 242 increasingly utilized for the creation of network services. Such a 243 control/management planes could be centralized, or be distributed. 245 2.5. Application of Service Policy 247 Service functions rely on topology information such as VLANs or 248 packet (re) classification to determine service policy selection, 249 i.e. the service function specific action taken. Topology 250 information is increasingly less viable due to scaling, tenancy and 251 complexity reasons. The topological information is often stale, 252 providing the operator with inaccurate placement that can result in 253 suboptimal resource utilization. Furthermore topology-centric 254 information often does not convey adequate information to the service 255 functions, forcing functions to individually perform more granular 256 classification. 258 2.6. Transport Dependence 260 Service functions can and will be deployed in networks with a range 261 of transports, including under and overlays. The coupling of service 262 functions to topology requires service functions to support many 263 transport encapsulations or for a transport gateway function to be 264 present. 266 2.7. Elastic Service Delivery 268 Given that the current state of the art for adding/removing service 269 functions largely centers around VLANs and routing changes, rapid 270 changes to the service deployment can be hard to realize due to the 271 risk and complexity of such changes. 273 2.8. Traffic Selection Criteria 275 Traffic selection is coarse, that is, all traffic on a particular 276 segment traverse service functions whether the traffic requires 277 service enforcement or not. This lack of traffic selection is 278 largely due to the topological nature of service deployment since the 279 forwarding topology dictates how (and what) data traverses service 280 function(s). In some deployments, more granular traffic selection is 281 achieved using policy routing or access control filtering. This 282 results in operationally complex configurations and is still 283 relatively inflexible. 285 2.9. Limited End-to-End Service Visibility 287 Troubleshooting service related issues is a complex process that 288 involve both network-specific and service-specific expertise. This 289 is especially the case when service function chains span multiple 290 DCs, or across administrative boundaries. Furthermore, the physical 291 and virtual environments (network and service), can be highly 292 divergent in terms of topology and that topological variance adds to 293 these challenges. 295 2.10. Per-Service (re)Classification 297 Classification occurs at each service function independent from 298 previously applied service functions. More importantly, the 299 classification functionality often differs per service function and 300 service functions may not leverage the results from other service 301 functions. 303 2.11. Symmetric Traffic Flows 305 Service function chains may be unidirectional or bidirectional 306 depending on the state requirements of the service functions. In a 307 unidirectional chain traffic is passed through a set of service 308 functions in one forwarding direction only. Bidirectional chains 309 require traffic to be passed through a set of service functions in 310 both forwarding directions. Many common service functions such as 311 DPI and firewall often require bidirectional chaining in order to 312 ensure flow state is consistent. 314 Existing service deployment models provide a static approach to 315 realizing forward and reverse service function chain association most 316 often requiring complex configuration of each network device 317 throughout the SFC. 319 2.12. Multi-vendor Service Functions 321 Deploying service functions from multiple vendors often require per- 322 vendor expertise: insertion models differ, there are limited common 323 attributes and inter- vendor service functions do not share 324 information. 326 3. Service Function Chaining 328 Service Function Chaining aims to address the aforementioned problems 329 associated with service deployment. Concretely, the SFC working 330 group will investigate solutions that address the following elements: 332 3.1. Service Overlay 334 Service function chaining utilizes a service specific overlay that 335 creates the service topology. The service overlay provides service 336 function connectivity and is built "on top" of the existing network 337 topology and allows operators to use whatever overlay or underlay 338 they prefer to create a path between service functions, and to locate 339 service functions in the network as needed. 341 Within the service topology, service functions can be viewed as 342 resources for consumption and an arbitrary topology constructed to 343 connect those resources in a required order. Adding new service 344 functions to the topology is easily accomplished, and no underlying 345 network changes are required. 347 Lastly, the service overlay can provide service specific information 348 needed for troubleshooting service-related issues. 350 3.2. Control Plane 352 Service aware control plane(s) provide information about the 353 available service functions on a network. The information provided 354 by the control plane includes service network location (for topology 355 creation), service type (e.g. firewall, load balancer, etc.) and, 356 optionally, administrative information about the service functions 357 such as load, capacity and operating status. The service aware 358 control plane allows for the formulation of service function chains 359 and exchanges requisite information needed to instantiate the service 360 function chains in the network. 362 Furthermore, the service aware control plane may interact with the 363 topology aware control plane (if separate) to ensure optimal 364 selection (and possibly placement) of service function within a 365 service function path. 367 3.3. Service Classification 369 Classification is used to select which traffic enters a service 370 overlay. The granularity of the classification varies based on 371 device capabilities, customer requirements, and service offered. 372 Initial classification determines the service function chain required 373 to process the traffic. Subsequent classification can be used within 374 a given service function chain to alter the sequence of service 375 functions applied. Symmetric classification ensures that forward and 376 reverse chains are in place. Similarly, asymmetric -- relative to 377 required service function -- chains can be achieved via service 378 classification. 380 3.4. Dataplane Metadata 382 Data plane metadata provides the ability to exchange information 383 between logical classification points and service functions (and vice 384 versa) and between service functions. As such metadata is not used 385 as forwarding information to deliver packets along the service 386 overlay. 388 Metadata can include the result of antecedent classification and/or 389 information from external sources. Service functions utilize 390 metadata, as required, for localized policy decisions. 392 In addition to sharing of information, the use of metadata addresses 393 several of the issues raised in section 2, most notably the de- 394 coupling of policy from the topology, and the need for per-service 395 classification (and re-classification). 397 A common approach to service metadata creates a common foundation for 398 interoperability between service functions, regardless of vendor. 400 4. Related IETF Work 402 The following subsections discuss related IETF work and are provided 403 for reference. This section is not exhaustive, rather it provides an 404 overview of the various initiatives and how they relate to network 405 service chaining. 407 1. [L3VPN]: The L3VPN working group is responsible for defining, 408 specifying and extending BGP/MPLS IP VPNs solutions. Although 409 BGP/MPLS IP VPNs can be used as transport for service chaining 410 deployments, the SFC WG focuses on the service specific 411 protocols, not the general case of VPNs. Furthermore, BGP/MPLS 412 IP VPNs do not address the requirements for service chaining. 414 2. [LISP]: LISP provides locator and ID separation. LISP can be 415 used as an L3 overlay to transport service chaining data but does 416 not address the specific service chaining problems highlighted in 417 this document. 419 3. [NVO3]: The NVO3 working group is chartered with creation of 420 problem statement and requirements documents for multi-tenant 421 network overlays. NVO3 WG does not address service chaining 422 protocols. 424 4. [ALTO]: The Application Layer Traffic Optimization Working Group 425 is chartered to provide topological information at a higher 426 abstraction layer, which can be based upon network policy, and 427 with application-relevant service functions located in it. The 428 mechanism for ALTO obtaining the topology can vary and policy can 429 apply to what is provided or abstracted. This work could be 430 leveraged and extended to address the need for services 431 discovery. 433 5. [I2RS]: The Interface to the Routing System Working Group is 434 chartered to investigate the rapid programming of a device's 435 routing system, as well as the service of a generalized, multi- 436 layered network topology. This work could be leveraged and 437 extended to address some of the needs for service chaining in the 438 topology and device programming areas. 440 6. [ForCES]: The ForCES working group has created a framework, 441 requirements, a solution protocol, a logical function block 442 library, and other associated documents in support of Forwarding 443 and Control Element Separation. The work done by ForCES may 444 provide a basis for both the separation of SFC elements, as well 445 as provide protocol and design guidance for those elements. 447 5. Summary 449 This document highlights problems associated with network service 450 deployment today and identifies several key areas that will be 451 addressed by the SFC working group. Furthermore, this document 452 identifies four components that are the basis for service function 453 chaining. These components will form the areas of focus for the 454 working group. 456 6. Security Considerations 458 Security considerations are not addressed in this problem statement 459 only document. Given the scope of service chaining, and the 460 implications on data and control planes, security considerations are 461 clearly important and will be addressed in the specific protocol and 462 deployment documents created by the SFC WG group. 464 7. Contributors 466 The following people are active contributors to this document and 467 have provided review, content and concepts (listed alphabetically by 468 surname): 470 Puneet Agarwal 471 Broadcom 472 Email: pagarwal@broadcom.com 474 Mohamed Boucadair 475 France Telecom 476 Email: mohamed.boucadair@orange.com 478 Abhishek Chauhan 479 Citrix 480 Email: Abhishek.Chauhan@citrix.com 482 Uri Elzur 483 Intel 484 Email: uri.elzur@intel.com 486 Kevin Glavin 487 Riverbed 488 Email: Kevin.Glavin@riverbed.com 490 Ken Gray 491 Cisco Systems 492 Email: kegray@cisco.com 494 Jim Guichard 495 Cisco Systems 496 Email:jguichar@cisco.com 498 Christian Jacquenet 499 France Telecom 500 Email: christian.jacquenet@orange.com 502 Surendra Kumar 503 Cisco Systems 504 Email: smkumar@cisco.com 506 Nic Leymann 507 Deutsche Telekom 508 Email: n.leymann@telekom.de 510 Darrel Lewis 511 Cisco Systems 512 Email: darlewis@cisco.com 514 Rajeev Manur 515 Broadcom 516 Email:rmanur@broadcom.com 518 Brad McConnell 519 Rackspace 520 Email: bmcconne@rackspace.com 522 Carlos Pignataro 523 Cisco Systems 524 Email: cpignata@cisco.com 526 Michael Smith 527 Cisco Systems 528 Email: michsmit@cisco.com 530 Navindra Yadav 531 Cisco Systems 532 Email: nyadav@cisco.com 534 8. Acknowledgments 536 The authors would like to thank David Ward, Rex Fernando, David 537 Mcdysan, Jamal Hadi Salim, Charles Perkins, Andre Beliveau, Joel 538 Halpern and Jim French for their reviews and comments. 540 9. Informative References 542 [ALTO] "Application-Layer Traffic Optimization (alto)", 543 . 545 [ForCES] "Forwarding and Control Element Separation (forces)", 546 . 548 [I2RS] "Interface to the Routing System (i2rs)", 549 . 551 [L3VPN] "Layer 3 Virtual Private Networks (l3vpn)", 552 . 554 [LISP] "Locator/ID Separation Protocol (lisp)", 555 . 557 [NVO3] "Network Virtualization Overlays (nvo3)", 558 . 560 [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network 561 Address Translator (Traditional NAT)", RFC 3022, 562 January 2001. 564 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 565 NAT64: Network Address and Protocol Translation from IPv6 566 Clients to IPv4 Servers", RFC 6146, April 2011. 568 [RFC6967] Boucadair, M., Touch, J., Levis, P., and R. Penno, 569 "Analysis of Potential Solutions for Revealing a Host 570 Identifier (HOST_ID) in Shared Address Deployments", 571 RFC 6967, June 2013. 573 Authors' Addresses 575 Paul Quinn (editor) 576 Cisco Systems, Inc. 578 Email: paulq@cisco.com 580 Thomas Nadeau (editor) 581 Brocade 583 Email: tnadeau@lucidvision.com