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Internet Engineering Task Force (IETF)                      M. Boucadair
Request for Comments: 9451                                        Orange
Updates: 8300                                                August 2023
Category: Standards Track                                               
ISSN: 2070-1721

Operations, Administration, and Maintenance (OAM) Packet and Behavior in

the Network Service Header (NSH)

Abstract

This document clarifies an ambiguity in the Network Service Header (NSH) specification related to the handling of O bit. In particular, this document clarifies the meaning of "OAM packet".

This document updates RFC 8300.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9451.

Copyright Notice

Copyright © 2023 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 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology
   3.  An Update to RFC 8300
   4.  IANA Considerations
   5.  Security Considerations
   6.  References
     6.1.  Normative References
     6.2.  Informative References
   Acknowledgments
   Author's Address

1. Introduction

This document clarifies an ambiguity related to the definition of the Operations, Administration, and Maintenance (OAM) packet discussed in [RFC8300].

Processing of the O bit in the Network Service Header (NSH) must follow the updated behavior specified in Section 3.

2. 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.

This document makes use of the terms defined in [RFC7665] and [RFC8300].

The document defines the following terms: 

   Service Function Chaining (SFC) data plane element:  refers to the
      SFC-aware Service Function (SF), Service Function Forwarder (SFF),
      SFC Proxy, or Classifier as defined in the SFC data plane
      architecture [RFC7665] and further refined in [RFC8300].
   
   OAM control element:  an NSH-aware element that is capable of
      generating NSH OAM packets.  An SFC data plane element may behave
      as an OAM control element.
   
   SFC OAM data:  refers to an OAM request (e.g., Connectivity
      Verification and Continuity Checks [RFC7276]), any data that
      influences how to execute a companion OAM request (e.g., identity
      of a terminating SF), the output data of an OAM request, and any
      combination thereof.
   
   User data:  refers to user packets cited in Section 5.7 of [RFC7665].

3. An Update to RFC 8300

This document updates Section 2.2 of [RFC8300] as follows:

OLD: 

   |  O bit:  Setting this bit indicates an OAM packet (see [RFC6291]).
   |     The actual format and processing of SFC OAM packets is outside
   |     the scope of this specification (for example, see [SFC-OAM-
   |     FRAMEWORK] for one approach).
   |  
   |     The O bit MUST be set for OAM packets and MUST NOT be set for
   |     non-OAM packets.  The O bit MUST NOT be modified along the SFP.
   |  
   |     SF/SFF/SFC Proxy/Classifier implementations that do not support
   |     SFC OAM procedures SHOULD discard packets with O bit set, but
   |     MAY support a configurable parameter to enable forwarding
   |     received SFC OAM packets unmodified to the next element in the
   |     chain.  Forwarding OAM packets unmodified by SFC elements that
   |     do not support SFC OAM procedures may be acceptable for a
   |     subset of OAM functions, but it can result in unexpected
   |     outcomes for others; thus, it is recommended to analyze the
   |     impact of forwarding an OAM packet for all OAM functions prior
   |     to enabling this behavior.  The configurable parameter MUST be
   |     disabled by default.

NEW: 

   |  O bit:  Setting this bit indicates an NSH OAM packet.  Such a
   |     packet is any NSH-encapsulated packet that exclusively includes
   |     SFC OAM data.  SFC OAM data can be included in the Fixed-Length
   |     Context Header, optional Context Headers, and/or the inner
   |     packet.
   |  
   |     The O bit is typically set by an OAM controller or a final
   |     destination of an NSH OAM packet that triggers a response
   |     (e.g., a specific SFC-aware SF or the last SFF of an SFP).
   |  
   |     The O bit MUST be set for NSH OAM packets and MUST NOT be set
   |     for non-OAM packets.  The O bit MUST NOT be modified along the
   |     SFP.
   |  
   |     NSH-encapsulated packets that include user data are not
   |     considered NSH OAM packets even if some SFC OAM data (e.g.,
   |     record route) is also supplied in the packet.
   |  
   |     When SFC OAM data is included in the inner packet, the Next
   |     Protocol field is set to reflect the structure of that inner
   |     OAM packet.  The setting and processing of the O bit neither
   |     assumes nor expects detailed analysis of the content of any
   |     inner IP packet carried by the NSH.  In order to prevent non-
   |     deterministic behaviors, SFC data plane elements MAY support a
   |     configuration parameter to filter valid Next Protocol values in
   |     NSH OAM packets.  Absent explicit configuration, SFFs, SFC-
   |     aware SFs, and SFC Proxies SHOULD discard any NSH packets with
   |     the O bit set and Next Protocol set to something that is not
   |     itself an OAM protocol.  This includes discarding the packet
   |     when the O bit is set and the Next Protocol is set to 0x01
   |     (IPv4), 0x02 (IPv6), 0x03 (MPLS), or 0x05 (Ethernet).
   |  
   |     An NSH OAM packet MAY include optional Context Headers (e.g., a
   |     subscriber identifier [RFC8979] or a flow identifier [RFC9263])
   |     that are used to influence the processing of the packet by SFC
   |     data plane elements.
   |  
   |     An NSH OAM packet MAY include SFC OAM data in both Context
   |     Headers and the inner packet.  The processing of the SFC OAM
   |     data (including the order) SHOULD be specified in the relevant
   |     OAM or Context Header specification.
   |  
   |     SFC-aware implementations of SF, SFF, SFC Proxy, and Classifier
   |     that do not support SFC OAM procedures SHOULD discard packets
   |     with the O bit set but MAY support a configurable parameter to
   |     enable forwarding received NSH OAM packets unmodified to the
   |     next element in the chain.  Forwarding NSH OAM packets
   |     unmodified by SFC data plane elements that do not support SFC
   |     OAM procedures may be acceptable for a subset of OAM functions,
   |     but it can result in unexpected outcomes for others.  Thus, it
   |     is recommended to analyze the impact of forwarding an NSH OAM
   |     packet for all OAM functions prior to enabling this behavior.
   |     The configurable parameter MUST be disabled by default.
   |  
   |     The actual format and additional processing of NSH OAM packets
   |     is outside the scope of this specification.

4. IANA Considerations

This document has no IANA actions.

5. Security Considerations

Data plane SFC-related security considerations, including privacy, are discussed in Section 6 of [RFC7665] and Section 8 of [RFC8300]. Additional security considerations related to SFC OAM are discussed in Section 9 of [RFC8924].

Any data included in an NSH OAM packet SHOULD be integrity protected [RFC9145].

6. References

6.1. 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,
              <https://www.rfc-editor.org/info/rfc2119>.
   
   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.
   
   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,
              <https://www.rfc-editor.org/info/rfc8300>.
   
   [RFC9145]  Boucadair, M., Reddy.K, T., and D. Wing, "Integrity
              Protection for the Network Service Header (NSH) and
              Encryption of Sensitive Context Headers", RFC 9145,
              DOI 10.17487/RFC9145, December 2021,
              <https://www.rfc-editor.org/info/rfc9145>.

6.2. Informative References

   [RFC6291]  Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
              D., and S. Mansfield, "Guidelines for the Use of the "OAM"
              Acronym in the IETF", BCP 161, RFC 6291,
              DOI 10.17487/RFC6291, June 2011,
              <https://www.rfc-editor.org/info/rfc6291>.
   
   [RFC7276]  Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
              Weingarten, "An Overview of Operations, Administration,
              and Maintenance (OAM) Tools", RFC 7276,
              DOI 10.17487/RFC7276, June 2014,
              <https://www.rfc-editor.org/info/rfc7276>.
   
   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,
              <https://www.rfc-editor.org/info/rfc7665>.
   
   [RFC8924]  Aldrin, S., Pignataro, C., Ed., Kumar, N., Ed., Krishnan,
              R., and A. Ghanwani, "Service Function Chaining (SFC)
              Operations, Administration, and Maintenance (OAM)
              Framework", RFC 8924, DOI 10.17487/RFC8924, October 2020,
              <https://www.rfc-editor.org/info/rfc8924>.
   
   [RFC8979]  Sarikaya, B., von Hugo, D., and M. Boucadair, "Subscriber
              and Performance Policy Identifier Context Headers in the
              Network Service Header (NSH)", RFC 8979,
              DOI 10.17487/RFC8979, February 2021,
              <https://www.rfc-editor.org/info/rfc8979>.
   
   [RFC9263]  Wei, Y., Ed., Elzur, U., Majee, S., Pignataro, C., and D.
              Eastlake 3rd, "Network Service Header (NSH) Metadata Type
              2 Variable-Length Context Headers", RFC 9263,
              DOI 10.17487/RFC9263, August 2022,
              <https://www.rfc-editor.org/info/rfc9263>.

Acknowledgments

Thanks to Jim Guichard, Greg Mirsky, Joel Halpern, Christian Jacquenet, Dirk von-Hugo, Carlos Pignataro, and Frank Brockners for the comments.

Thanks to Barry Leiba for the art directorate review and Russ Housley for the security directorate review.

Thanks to Alvaro Retana and Robert Wilton for their IESG reviews.

Author's Address

   Mohamed Boucadair
   Orange
   35000 Rennes
   France
   Email: mohamed.boucadair@orange.com