SFC B. Sarikaya Internet-Draft Intended status: Standards Track D. von Hugo Expires: April 11, 2021 Deutsche Telekom M. Boucadair Orange October 8, 2020 Service Function Chaining: Subscriber and Performance Policy Identification Variable-Length Network Service Header (NSH) Context Headers draft-ietf-sfc-serviceid-header-10 Abstract This document defines Subscriber and Performance Policy Identifiers Network Service Header Variable-Length Context Headers to inform Service Functions about subscriber- and service-related information for the sake of policy enforcement and appropriate service function chaining operations. The structure of each Context Header, their use and processing by NSH-aware nodes are described. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on April 11, 2021. Copyright Notice Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of Sarikaya, et al. Expires April 11, 2021 [Page 1] Internet-Draft NSH Subscriber/Performance Policy TLVs October 2020 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4 3. Subscriber Identification NSH Variable-Length Context Header 4 4. Performance Policy Identification NSH Variable-Length Context Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 8.1. Normative References . . . . . . . . . . . . . . . . . . 9 8.2. Informative References . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction This document discusses how to inform Service Functions (SFs) [RFC7665] about subscriber and service-related information, when required, for the sake of policy enforcement within a single administrative domain. Particularly, subscriber-related information may be required to enforce subscriber-specific SFC-based traffic policies. However, the information carried in packets may not be sufficient to unambiguously identify a subscriber. This document fills this void by specifying a new Network Service Header (NSH) [RFC8300] Context Header to convey and disseminate such information within the boundaries of a single administrative domain. Also, the enforcement of SFC-based differentiated traffic policies may be inferred, for example, by QoS (Quality of Service) considerations. Typically, QoS information may serve as an input for the computation, establishment, and selection of the Service Function Path (SFP). Furthermore, the dynamic structuring of service function chains and their subsequent enforcement may be conditioned by QoS requirements that will affect SF instance(s) identification, location, and sequencing. Hence, the need to supply a performance policy identifier to downstream SFs to appropriately meet the service requirements arises. SFs and SF Forwarders (SFFs) involved in a service chain have to contribute to the respective service policy (QoS, for example) Sarikaya, et al. Expires April 11, 2021 [Page 2] Internet-Draft NSH Subscriber/Performance Policy TLVs October 2020 requirements characterized by low transmission delay between each other, by exposing a high availability of resources to process function tasks, or by redundancy provided by stand-by machines for seamless execution continuation in case of failures. These requirements may be satisfied by means of control plane protocols, but in some contexts, e.g., in networks where resources are very much constrained, carrying QoS-related information directly in packets may improve the overall SFC operation instead of relying upon the potential complexity or adding overhead introduced by some SFC control plane features. This information is proposed to be included as a Context Header in the NSH. The context information defined in this document can be applicable in the context of mobile networks (particularly, in the 3GPP defined (S)Gi Interface) [I-D.ietf-sfc-use-case-mobility]. Typically, because of the widespread use of private addressing in those networks, if SFs to be invoked are located after a NAT function, the identification based on the internal IP address is not possible once the NAT has been crossed. NAT functionality can reside in a distinct node which for 3GPP network can be the Packet Data Network (PDN) Gateway (PGW) as specified in [TS23401] in case of 4G or the User Plane Function (UPF) facing the external Data Network (DN) [TS23501] in case of 5G, respectively. As such, means to allow passing the internal information may optimise packet traversal within an SFC- enabled mobile network domain. Furthermore, some SFs that are not enabled on the PGW/UPF may require a subscriber identifier to properly operate. As such identifier one of already specified 3GPP identifiers may serve (see, for example, those listed in [RFC8371]), but it is out of scope of this document to include a comprehensive list of deployment contexts which may make use of the Context Headers defined in the document. Since identifiers for subscribers are distinct from those for performance policy and multiple policies (e.g., as per multiple services) may be associated to a single subscriber within one service chain both identifiers are defined separately thus avoiding to require additional internal structures of the Context Headers to decide unambiguously whether an identifier refers to a subscriber or to a policy. This document does not make any assumption about the structure of subscriber or performance policy identifiers; each such identifier is treated as an opaque value. The semantics and validation of these identifiers are policies local to an SFC-enabled domain. This document focuses on the data plane behaviour. Control plane considerations are out of the scope. Sarikaya, et al. Expires April 11, 2021 [Page 3] Internet-Draft NSH Subscriber/Performance Policy TLVs October 2020 The reader may refer to Section 3 of [RFC8300] for MTU considerations. Such considerations are not reiterated here. This document assumes the NSH is used exclusively within a single administrative domain. This document adheres to the SFC data plane architecture defined in [RFC7665]. This document assumes the reader is familiar with [RFC8300]. 2. Conventions and Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119][RFC8174] when, and only when, they appear in all capitals, as shown here. The reader should be familiar with the terms defined in [RFC7665]. SFC Control Element refers to a logical entity that instructs one or more SFC data plane functional elements on how to process packets within an SFC-enabled domain. 3. Subscriber Identification NSH Variable-Length Context Header Subscriber Identifier is defined as an optional variable-length NSH Context Header. Its structure is shown in Figure 1. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Metadata Class | Type |U| Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Subscriber Identifier ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Subscriber Identifier Variable-Length Context Header The description of the fields is as follows: o Metadata Class: MUST be set to 0x0 [RFC8300]. o Type: TBD1 (See Section 5). o U bit: Unassigned bit (see Section 2.5.1 of [RFC8300]). Sarikaya, et al. Expires April 11, 2021 [Page 4] Internet-Draft NSH Subscriber/Performance Policy TLVs October 2020 o Length: Indicates the length of the Subscriber Identifier, in bytes (see Section 2.5.1 of [RFC8300]). o Subscriber Identifier: Carries an opaque subscriber identifier. The Subscriber Identifier Context Header is used to convey an identifier assigned by the service provider to uniquely identify a subscriber. This subscriber identifier can be used by service functions to enforce per-subscriber policies (e.g., apply resource quota). The classifier and NSH-aware SFs MAY inject or strip a subscriber identifier Context Header as a function of a local policy. In order to prevent interoperability issues, the data and their format to be injected in such header SHOULD be configured to nodes authorized to inject such headers. Typically, a node can be instructed to insert such data following a type/set scheme (e.g., node X should inject subscriber ID type Y). Other schemes may be envisaged. Failures to inject such headers SHOULD be logged locally while a notification alarm MAY be sent to a Control Element. The details of sending notification alarms (i.e., the parameters affecting the transmission of the notification alarms depend on the information in the Context Header such as frequency, thresholds, and content of the alarm (full header, timestamp, etc.)) SHOULD be configurable. This document adheres to the recommendations in [RFC8300] for handling the Context Headers at both ingress and egress SFC boundary nodes. That is, to strip such Context Headers. Revealing any personal and subscriber-related information to third parties is avoided by design to prevent privacy breaches in terms of user tracking. Depending on the local policy, proxies MAY strip a Subscriber Identifier Context Header from the packet or pass the data to the next SF in the service chain after processing the content of the Context Headers. If no instruction is provided, an intermediary NSH- aware node MUST maintain such Context Headers so that the information can be passed to next hop NSH-aware nodes. NSH-aware SFs MUST ignore Context Headers carrying unknown subscriber identifiers. NSH-aware SFs MUST be capable to run additional validation checks on the content of these Context Headers (e.g., accept only some lengths, types) and the behavior to adopt; the exact set of validation checks are provided as a local policy. Such policy may include to, e.g., ignore the Context Header or to remove it from the packet. However, Sarikaya, et al. Expires April 11, 2021 [Page 5] Internet-Draft NSH Subscriber/Performance Policy TLVs October 2020 this specification does not require nor preclude such NSH-aware SFs may be instructed to ignore the Context Header, to remove the Context Header from the packet, etc. These validation checks are deployment- specific. If validation checks fail on a Subscriber Identifier Context Header, an NSH-aware SF MUST ignore that Context Header. The event SHOULD be logged locally while a notification alarm MAY be sent to a Control Element if the NSH-aware SF is instructed to do so. For example, an SF that expects an internal IP address as subscriber identifier will discard Subscriber Identifier Context Headers conveying Mobile Subscriber ISDN Number (MSISDN), International Mobile Subscriber Identity (IMSI), or malformed IP addresses. Multiple Subscriber Identifier Context Headers MAY be present in the NSH, each carrying a distinct opaque value but all pointing to the same subscriber. This may be required, e.g., by policy enforcement mechanisms in a mobile network where some SFs rely on IP addresses as subscriber Identifiers, while others use non-IP specific identifiers such as those listed in [RFC8371] and Section 3.3.2 of [I-D.ietf-sfc-use-case-mobility]. When multiple subscriber identifier Context Headers are present and an SF is instructed to strip the Subscriber Identifier Context Header, that SF MUST remove all Subscriber Identifier Context Headers. 4. Performance Policy Identification NSH Variable-Length Context Headers Dedicated service-specific performance identifier is defined to differentiate between services requiring specific treatment to exhibit a performance characterized by, e.g., ultra-low latency (ULL) or ultra-high reliability (UHR). Other policies can be considered when instantiating a service function chain within an SFC-enabled domain. They are conveyed in the Performance Policy Identifier Context Header. The Performance Policy Identifier Context Header is inserted in an NSH packet so that downstream NSH-aware nodes can make use of the performance information for proper distributed SFC path selection, SF instance selection, or policy selection at SFs. Note that the use of the Performance Policy Identifier is not helpful if the path computation is centralized and a strict SFP is presented as local policy to SFFs. The Performance Policy Identifier allows for the distributed enforcement of a per-service policy such as a service function path to only include specific SFs instances (e.g., SFs located within the same DC or those that are exposing the shortest delay from an SFF). Details of this process are implementation-specific. For illustration purposes, an SFF may retrieve the details of usable SFs Sarikaya, et al. Expires April 11, 2021 [Page 6] Internet-Draft NSH Subscriber/Performance Policy TLVs October 2020 based upon the corresponding performance policy identifier. Typical criteria for instantiating specific SFs include location, performance, or proximity considerations. For the particular case of UHR services, the stand-by operation of back-up capacity or the deployment of multiple SF instances may be requested. In an environment characterised by frequent changes of link and path behaviour, for example due to variable load or availablility caused by propagation conditions on a wireless link, the SFP may have to be adapted dynamically by on-the move SFC path and SF instance selection. Performance Policy Identifier is defined as optional variable length Context Header. Its structure is shown in Figure 2. Depending on the local policy, proxies MAY strip a Performance Policy Identifier Context Header from the packet or pass the data to the next SF in the service chain after processing the content of the Context Headers. If no instruction is provided, an intermediary NSH- aware node MUST maintain such Context Headers so that the information can be passed to next hop NSH-aware nodes. Multiple Performance Policy Identifier Context Headers MAY be present in the NSH; each carrying an opaque value for a distinct policy that need to be enforced for a flow. Supplying ocnlficting policies may complicate the SFP computation and SF instance location. Corresponding rules to detect conflicting policies may be provided as a local policy to the NSH-aware nodes. When such conflict is detected by an NSH-aware node, the default behavior of the node is to discard the packet and send a notification alarm to a Control Element. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Metadata Class | Type |U| Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Performance Policy Identifier ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Performance Policy Identifier Variable-Length Context Header The description of the fields is as follows: o Metadata Class: MUST be set to 0x0 [RFC8300]. Sarikaya, et al. Expires April 11, 2021 [Page 7] Internet-Draft NSH Subscriber/Performance Policy TLVs October 2020 o Type: TBD2 (See Section 5). o U bit: Unassigned bit (see Section 2.5.1 of [RFC8300]). o Length: Indicates the length of the Performance Policy Identifier, in bytes (see Section 2.5.1 of [RFC8300]). o Performance Policy Identifier: Represents an opaque value pointing to specific performance policy to be enforced. The structure and semantic of this field is deployment-specific. 5. IANA Considerations This document requests IANA to assign the following types from the "NSH IETF- Assigned Optional Variable-Length Metadata Types" (0x0000 IETF Base NSH MD Class) registry available at: https://www.iana.org/assignments/nsh/nsh.xhtml#optional-variable- length-metadata-types. +-------+-------------------------------+----------------+ | Value | Description | Reference | +-------+-------------------------------+----------------+ | TBD1 | Subscriber Identifier | [ThisDocument] | | TBD2 | Performance Policy Identifier | [ThisDocument] | +-------+-------------------------------+----------------+ 6. Security Considerations Data plane SFC-related security considerations, including privacy, are discussed in [RFC7665] and [RFC8300]. Nodes that are involved in an SFC-enabled domain are assumed to be trusted ([RFC8300]). Means to check that only authorized nodes are solicited when a packet is crossing an SFC-enabled domain are out of scope of this document. A misbehaving node within from the SFC-enabled domain may alter the content of Subscriber Identifier and Performance Policy Context Headers which may lead to service disruption. Such attack is not unique to the Context Headers defined in this document; measures discussed in [RFC8300] are to be followed. An SF maintaining logs for operational reasons MUST NOT log the content of Subscriber and Performance Policy Context Headers received in NSH packets if the SF does not use the content of that header for its operation. Sarikaya, et al. Expires April 11, 2021 [Page 8] Internet-Draft NSH Subscriber/Performance Policy TLVs October 2020 7. Acknowledgements Comments from Joel Halpern on a previous version and by Carlos Bernardos are appreciated. Contributions and review by Christian Jacquenet, Danny Lachos, Debashish Purkayastha, Christian Esteve Rothenberg, Kyle Larose, Donald Eastlake, Qin Wu, Shunsuke Homma, and Greg Mirsky are thankfully acknowledged. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/RFC7665, October 2015, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed., "Network Service Header (NSH)", RFC 8300, DOI 10.17487/RFC8300, January 2018, . 8.2. Informative References [I-D.ietf-sfc-use-case-mobility] Haeffner, W., Napper, J., Stiemerling, M., Lopez, D., and J. Uttaro, "Service Function Chaining Use Cases in Mobile Networks", draft-ietf-sfc-use-case-mobility-09 (work in progress), January 2019. [RFC8371] Perkins, C. and V. Devarapalli, "Mobile Node Identifier Types for MIPv6", RFC 8371, DOI 10.17487/RFC8371, July 2018, . Sarikaya, et al. Expires April 11, 2021 [Page 9] Internet-Draft NSH Subscriber/Performance Policy TLVs October 2020 [RFC8459] Dolson, D., Homma, S., Lopez, D., and M. Boucadair, "Hierarchical Service Function Chaining (hSFC)", RFC 8459, DOI 10.17487/RFC8459, September 2018, . [TS23401] 3GPP 23.401 16.5.0, "General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access,", December 2019. [TS23501] 3GPP 23.501 16.3.0, "System architecture for the 5G System (5GS),", December 2019. Authors' Addresses Behcet Sarikaya Email: sarikaya@ieee.org Dirk von Hugo Deutsche Telekom T-Online-Allee 1 D-64295 Darmstadt Germany Email: Dirk.von-Hugo@telekom.de Mohamed Boucadair Orange Rennes 3500 France Email: mohamed.boucadair@orange.com Sarikaya, et al. Expires April 11, 2021 [Page 10]