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Drake 4 Intended status: Standards Track Juniper Networks 5 Expires: April 30, 2018 October 27, 2017 7 Operating the Network Service Header (NSH) with Next Protocol "None" 8 draft-farrel-sfc-convent-03 10 Abstract 12 This document describes the use of the Network Service Header (NSH) 13 in a Service Function Chaining (SFC) enabled network with no payload 14 data and carrying only metadata. This is achieved by defining a new 15 NSH "Next Protocol" type value of "None". 17 This document illustrates some of the functions that may be achieved 18 or enhanced by this mechanism, but it does not provide an exhaustive 19 list of use cases, nor is it intended to be definitive about the 20 functions it describes. It is expected that other documents will 21 describe specific use cases in more detail and will define the 22 protocol mechanics for each use case. 24 Requirements Language 26 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 27 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 28 document are to be interpreted as described in [RFC2119]. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on April 30, 2018. 47 Copyright Notice 49 Copyright (c) 2017 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 65 2. The Network Service Header . . . . . . . . . . . . . . . . . 3 66 2.1. Next Protocol 'None' . . . . . . . . . . . . . . . . . . 4 67 3. Processing Rules . . . . . . . . . . . . . . . . . . . . . . 4 68 4. Backward Compatibility . . . . . . . . . . . . . . . . . . . 5 69 5. Overview of Use Cases . . . . . . . . . . . . . . . . . . . . 5 70 5.1. Per-SFP Metadata . . . . . . . . . . . . . . . . . . . . 5 71 5.2. Per-Flow Metadata . . . . . . . . . . . . . . . . . . . . 6 72 5.3. Coordination Between SFC-Aware SFIs . . . . . . . . . . . 6 73 5.4. Operations, Administration, and Maintenance (OAM) . . . . 7 74 5.5. Control Plane and Management Plane Uses . . . . . . . . . 7 75 5.6. Non-Applicable Use Cases . . . . . . . . . . . . . . . . 8 76 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 77 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 78 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9 79 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 80 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 81 10.1. Normative References . . . . . . . . . . . . . . . . . . 9 82 10.2. Informative References . . . . . . . . . . . . . . . . . 9 83 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 85 1. Introduction 87 An architecture for Service Function Chaining (SFC) is presented in 88 [RFC7665]. That architecture enables packets to be forwarded along 89 Service Function Paths (SFPs) to pass through various Service 90 Functions (SFs) that act on the packets. Each packet is encapsulated 91 with a Network Service Header (NSH) [I-D.ietf-sfc-nsh] that 92 identifies the SFP that the packet travels along (by means of a 93 Service Path Identifier - SPI) and the hop (i.e., the next SF to be 94 executed) along the SFP that the packet has reached (by means of a 95 Service Index - SI). The SPI and SI are fields encoded in the NSH. 97 Packets are classified at the SFC network ingress boundaries by 98 Classifiers (section 4.4 of [RFC7665]) and have an NSH applied to 99 them. Such packets are forwarded between Service Function Forwarders 100 (SFFs) using tunnels across the underlay network, and each SFF may 101 hand the packet off to one or more Service Function Instances (SFIs) 102 according to the definition of the SFP. 104 The SFC Classifier or any SFC-aware SFI may wish to share information 105 (possibly state information) about the SFP, the traffic flow, or a 106 specific packet, and they may do this by adding "metadata" to packets 107 as part of the NSH. Metadata may be used to enhance or enable the 108 function preformed by SFC-aware SFs, may enable coordination and data 109 exchange between SFIs, or may be used to assist a network operator in 110 the diagnosis and monitoring of an SFP. The nature of metadata to be 111 supplied and consumed is implementation- and deployment-specific. 113 This document defines a mechanism for metadata to be carried on an 114 SFP without the need for payload data. This may enable diagnosis and 115 monitoring of SFPs, and coordination between SFC-aware SFIs, without 116 the need for traffic to be flowing, and without the need to rewrite 117 data packets to insert what might be substantial amounts of metadata. 119 This function is achieved by defining a new value for the NSH "Next 120 Protocol" field to indicate "None". Such packets are contained 121 within the SFC-enabled domain. 123 This document illustrates some of the functions that may be achieved 124 or enhanced by this mechanism, but it does not provide an exhaustive 125 list of use cases, nor is it intended to be definitive about the 126 functions it describes. It is expected that other documents will 127 describe specific use cases in more detail and will define the 128 protocol mechanics for each use case. 130 2. The Network Service Header 132 The NSH is defined in [I-D.ietf-sfc-nsh]. It includes a field called 133 "Next Protocol" that is used to indicate the nature of the payload 134 data that follows the NSH. The field can be used by any component 135 that processes the NSH (for example, to understand how to interpret 136 and parse the payload) and by nodes at the end of the SFP that remove 137 the NSH and forward the payload data. 139 2.1. Next Protocol 'None' 141 This document defines a new value for the "Next Protocol" field. 142 When set to TBD1, the field indicates that the next protocol is 143 "None" meaning that there is no user/payload data following the NSH. 145 When the next protocol is "None" the rest of the NSH still has 146 meaning and, in particular, the metadata carried in the NSH may still 147 be present. 149 3. Processing Rules 151 An SFC-aware node wishing to send metadata without a data packet: 153 o MUST create a packet carrying an NSH and the desired metadata 155 o MUST set the "Next Protocol" field to TBD1 157 o SHOULD ensure that there are no bytes following the end of the NSH 158 (i.e., that there is no payload data) 160 o MUST encapsulate and send the packet as normal for tunneling to 161 the next hop on the SFP as would be done for any NSH packet (i.e., 162 for a data packet following the SFP). 164 A packet with no payload data may be inserted at the head end of an 165 SFP (such as at a Classifier) and may be easily forwarded by an SFF 166 or SFI on the SFP using the processing rules defined in 167 [I-D.ietf-sfc-nsh]. 169 A packet with no payload may also be generated by an SFC-aware SFI as 170 a result of processing an incoming packet (i.e., triggered by a 171 condition arising from processing a normal NSH packet with a 172 payload). In such cases, the SPI/SI can be inherited from the 173 original packet or can be set according to information supplied 174 through the control plane, or management plane, or indicated by 175 information carried in the metadata of the data packet. This 176 document does not further specify the triggers to generate an NSH 177 packet with a "Next Protocol" set to "None". 179 A transit node (SFF, SFI, or Classifier) receiving a packet with 180 "Next Protocol" indicating "None" MUST NOT attempt to parse or 181 process beyond the end of the NSH, but SHOULD process the NSH and the 182 metadata as normal. 184 A node that is the egress of an SFP would normally strip the NSH and 185 forward the payload according to the setting of the "Next Protocol" 186 field. Such nodes MUST NOT forward packets with "Next Protocol" 187 indicating "None" even if there are some bytes after the NSH. 189 4. Backward Compatibility 191 The procedures for handling NSH fields with unknown values are set 192 out in [I-D.ietf-sfc-nsh]. In particular, section 2.2 of 193 [I-D.ietf-sfc-nsh] describes how elements of an SFC enabled network 194 handle unknown values of the "Next Protocol" field. 196 SFC-aware nodes that do not understand the meaning of a value 197 contained in the "Next Protocol" field of the NSH are unable to parse 198 the payload. Such nodes silently drop packets with unknown "Next 199 Protocol" values unless explicitly configured to forward them. 201 All this means that legacy SFC-aware nodes that are unaware of the 202 meaning of the "Next Protocol" value "None" will act as follows: 204 o SFFs can be configured to forward the packets 206 o SFC Proxies will drop the packets 208 o SFIs will most likely drop the packets 210 o Reclassifiers will most likely drop the packets 212 SFC-aware nodes at the end of an SFP possibly forward packets with no 213 knowledge of the payload in a "pop and forward" form of processing 214 where the NSH is removed and the packet is simply put on an interface 215 and the payload protocol is known a priori (or assumed). It is a 216 general processing rule for all forwarders that they SHOULD NOT 217 attempt to send packets with zero length, and packets with the NSH 218 "Next Protocol" set to "None" are expected to have zero payload 219 length. In any case, SFC-aware nodes at the end of an SFP MUST NOT 220 forward packets with "Next Protocol" set to "None". 222 5. Overview of Use Cases 224 5.1. Per-SFP Metadata 226 Per-SFP metadata is metadata that applies to an SFP and any data 227 packets on that SFP. It does not need to be transmitted with every 228 packet, but can be installed at the SFIs on the SFP and applied to 229 all packets on the SFP. It could be installed by inclusion in the 230 NSH of a data packet sent on the SFP, by out of band control or 231 management plane mechanisms, or by separate metadata-only packets 232 using "Next Protocol" set to "None" as described in this document. 234 Per-SFP metadata-only packets may be sent along the path of an SFP 235 simply by setting the correct SPI in the NSH, and setting the SI to 236 the correct value for the hop of the SFP at which the metadata is to 237 be introduced. Classifiers and reclassifiers will know the correct 238 SI values to be used from information supplied by the control or 239 management plane as is the case for NSH packets with payload data. 241 5.2. Per-Flow Metadata 243 Per-flow metadata is metadata that applies to a subset of the packets 244 on an SFP, such as packets matching a particular 5 tuple of source 245 address, destination address, source port, destination port, and 246 payload protocol. This metadata also does not need to be transmitted 247 with every packet, but can be installed at the SFIs on the SFP and 248 applied to the packets that match the flow description. 250 If there is just one flow on an SFP then there is no difference 251 between per-flow metadata and per-SFP metadata as described in 252 Section 5.1. 254 In normal processing, the flow to which per-flow metadata applies can 255 be deduced by looking at the payload data in the context of the value 256 of the "Next Protocol" field. However, when "Next Protocol" 257 indicates "None" this cannot be done. In this case the identity of 258 the flow is carried in the metadata itself. 260 5.3. Coordination Between SFC-Aware SFIs 262 A pair of SFC-aware SFIs (adjacent or not) on an SFP may desire to 263 coordinate state and may do this by sending information encoded in 264 metadata. 266 To do this using the mechanisms defined in this document: 268 o There must be an SFP that passes through the two SFIs in the 269 direction of sender to receiver. 271 o The sender must know the correct SPI to use. 273 o The sender must know the correct SI to use for the point at which 274 it resides on the SFP. 276 o Ideally the receiver will know to remove the packet from the SFP 277 and not forward it further as this might share metadata wider than 278 desirable and would cause unnecessary packets in the network. 279 Note, however, that continued forwarding of such packets would not 280 be substantially harmful in its own right. 282 Note that technically (according to the SFC architecture) the process 283 of inserting a packet into an SFP is performed by a Classifier. 284 However, a Classifier may be co-resident with an SFI so an 285 implementation of an SF may also be able to generate NSH packets as 286 described in this document. 288 Note also that a system with SFIs that need to coordinate between 289 each other may be configured so that there is a specific, dedicated 290 SFP between those service functions that is used solely for this 291 purpose. Thus, such an SFI does not need to insert NSH packets onto 292 SFPs used to carry payload data, but can use (and know the SPI of) 293 this special, dedicated SFP. 295 5.4. Operations, Administration, and Maintenance (OAM) 297 Requirements for Operations, Administration, and Maintenance (OAM) in 298 SFC networks are discussed in [I-D.ietf-sfc-oam-framework]. The NSH 299 definition in [I-D.ietf-sfc-nsh] includes an O-bit that indicates 300 that packet contains OAM information. 302 If OAM information is carried in packets that also include payload 303 data, that information must be carried in metadata. Therefore, the 304 mechanism defined in this document can also be used to carry OAM 305 information independent of payload data. 307 Sending OAM separate from (but interleaved with) packets that carry 308 payload data may have several advantages including: 310 o Sending OAM when there is no other traffic flowing. 312 o Sending OAM at predictable intervals. 314 o Measuring path qualities distinct from behavior of SFIs. 316 o Sending OAM without needing to rewrite payload data buffers. 318 o Keeping OAM processing components separate from other processing 319 components. 321 5.5. Control Plane and Management Plane Uses 323 As described in Section 5.3, SFPs can be established specifically to 324 carry metadata-only packets. And as described in Section 5.1, 325 metadata-only packets can be sent down existing SFPs. This means 326 that metadata-only packets can be used to carry control plane and 327 management plane messages used to control and manage the SFC network. 329 In effect, SFPs can be established to serve as a Data Control Network 330 (DCN) or Management Control Network (MCN). Further details of this 331 process are out of scope of this document, but it should be 332 understood that, just as for OAM, an essential feature of using a 333 control channel is that the various speakers are assigned identifiers 334 (i.e., addresses). In this case, those identifiers could be SPI/SI 335 pairs, or could be IP addresses as used in the normal control and 336 management plane of the SFC network. 338 5.6. Non-Applicable Use Cases 340 Per-packt metadata is metadata that applies specifically to a single 341 payload packet. It informs an SFI how to handle the payload packet, 342 and does not apply to any other packet. 344 The mechanisms described in this document are not applicable to per- 345 packet metadata because, by definition, if the "Next Protocol" 346 indicates "None" then there is no packet following the NSH for the 347 metadata to be associated with. 349 6. Security Considerations 351 Metadata-only packets as enabled by this document provide a covert 352 channel. However, this is only different from the metadata feature 353 in the normal NSH in that it can be sent without the presence of a 354 data flow. 356 Metadata may, of course, contain sensitive data and may also contain 357 information used to control the behavior of SFIs in the network. As 358 such, this data needs to be protected according to its value and 359 according to the perceived vulnerabilities of the network. 360 Protection of metadata may be achieved by using encrypted transport 361 between SFC entities or by encrypting the metadata in its own right. 362 The need to protect the metadata is not modified by this document and 363 forms part of the NSH definition found in [I-D.ietf-sfc-nsh]. 365 The mechanism described in this document might possibly be used to 366 introduce packets into the SFC overlay network. Therefore measures 367 SHOULD be taken to ensure authorization of sources of such packets, 368 and tunneling of such packets into the network SHOULD be prevented. 369 The amount of packets with "Next Protocol" set to "None" on an SFP 370 MAY be rate limited at any point on the SFP to provide additional 371 security. 373 Further discussion of NSH security is presented in 374 [I-D.ietf-sfc-nsh]. 376 7. IANA Considerations 378 IANA has been requested to create a registry of "Next Protocol" 379 values in [I-D.ietf-sfc-nsh]. This document requests IANA to 380 allocate a value from that registry to indicate "None" (TBD1 in this 381 document). 383 It is strongly suggested that a value of 0 (zero) be assigned. 385 8. Contributors 387 Lucy Yong 388 Retired 390 9. Acknowledgements 392 Thanks to the attendees at the SFC interim meeting in Westford in 393 January 2017 for discussions that suggested the value of this 394 document. 396 Thanks to Eric Rosen and Med Boucadair for valuable review comments. 398 10. References 400 10.1. Normative References 402 [I-D.ietf-sfc-nsh] 403 Quinn, P., Elzur, U., and C. Pignataro, "Network Service 404 Header (NSH)", draft-ietf-sfc-nsh-27 (work in progress), 405 October 2017. 407 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 408 Requirement Levels", BCP 14, RFC 2119, 409 DOI 10.17487/RFC2119, March 1997, 410 . 412 10.2. Informative References 414 [I-D.ietf-sfc-oam-framework] 415 Aldrin, S., Pignataro, C., Kumar, N., Akiya, N., Krishnan, 416 R., and A. Ghanwani, "Service Function Chaining (SFC) 417 Operation, Administration and Maintenance (OAM) 418 Framework", draft-ietf-sfc-oam-framework-03 (work in 419 progress), September 2017. 421 [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function 422 Chaining (SFC) Architecture", RFC 7665, 423 DOI 10.17487/RFC7665, October 2015, 424 . 426 Authors' Addresses 428 Adrian Farrel 429 Juniper Networks 431 Email: afarrel@juniper.net 433 John Drake 434 Juniper Networks 436 Email: jdrake@juniper.net