RFC9452: Network Service Header (NSH) Encapsulation for In Situ OAM (IOAM) Data

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Related keywords:  (In-situ) (inband) (telemetry) (tracing)

Internet Engineering Task Force (IETF)                 F. Brockners, Ed.
Request for Comments: 9452                                         Cisco
Category: Standards Track                               S. Bhandari, Ed.
ISSN: 2070-1721                                              Thoughtspot
                                                             August 2023

 Network Service Header (NSH) Encapsulation for In Situ OAM (IOAM) Data


   In situ Operations, Administration, and Maintenance (IOAM) is used
   for recording and collecting operational and telemetry information
   while the packet traverses a path between two points in the network.
   This document outlines how IOAM-Data-Fields are encapsulated with the
   Network Service Header (NSH).

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

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   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Conventions
   3.  IOAM Encapsulation with NSH
   4.  IANA Considerations
   5.  Security Considerations
   6.  References
     6.1.  Normative References
     6.2.  Informative References
   Appendix A.  Discussion of the IOAM-Encapsulation Approach
   Authors' Addresses

1.  Introduction

   IOAM, as defined in [RFC9197], is used to record and collect OAM
   information while the packet traverses a particular network domain.
   The term "in situ" refers to the fact that the OAM data is added to
   the data packets rather than what is being sent within packets
   specifically dedicated to OAM.  This document defines how IOAM-Data-
   Fields are transported as part of the Network Service Header (NSH)
   encapsulation [RFC8300] for the Service Function Chaining (SFC)
   Architecture [RFC7665].  The IOAM-Data-Fields are defined in

2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.

   Abbreviations used in this document:

   IOAM:  In situ Operations, Administration, and Maintenance

   MD:  NSH Metadata, see [RFC7665]

   NSH:  Network Service Header

   OAM:  Operations, Administration, and Maintenance

   SFC:  Service Function Chaining

   TLV:  Type, Length, Value

3.  IOAM Encapsulation with NSH

   The NSH is defined in [RFC8300].  IOAM-Data-Fields are carried as NSH
   payload using a Next Protocol header that follows the NSH headers.
   An IOAM header containing the IOAM-Data-Fields is added.  The IOAM-
   Data-Fields MUST follow the definitions corresponding to IOAM Option-
   Types (e.g., see Section 4 of [RFC9197] and Section 3.2 of
   [RFC9326]).  In an administrative domain where IOAM is used,
   insertion of the IOAM header in NSH is enabled at the NSH tunnel
   endpoints, which are also configured to serve as encapsulating and
   decapsulating nodes for IOAM.  The operator MUST ensure that SFC-
   aware nodes along the Service Function Path support IOAM; otherwise,
   packets might be dropped (see the last paragraph of this section as
   well as Section 2.2 of [RFC8300]).  The IOAM transit nodes (e.g., a
   Service Function Forwarder (SFF)) MUST process all the IOAM headers
   that are relevant based on its configuration.  See [RFC9378] for a
   discussion of deployment-related aspects of IOAM-Data-Fields.

    0                   1                   2                   3
    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
   |Ver|O|U|    TTL    |   Length  |U|U|U|U|MD Type| NP = 0x06  |  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  N
   |          Service Path Identifier              | Service Index |  S
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  H
   |                            ...                                |  |
   |  IOAM-Type    | IOAM HDR Len  |    Reserved   | Next Protocol |  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  I
   !                                                               |  O
   !                                                               |  A
   ~                 IOAM Option and Optional Data Space           ~  M
   |                                                               |  |
   |                                                               |  |
   |                                                               |
   |                                                               |
   |                 Payload + Padding (L2/L3/...)                 |
   |                                                               |
   |                                                               |
   |                                                               |

                                  Figure 1

   The NSH header and fields are defined in [RFC8300].  The O bit MUST
   be handled following the rules in [RFC9451].  The "NSH Next Protocol"
   value (referred to as "NP" in the diagram above) is 0x06.

   The IOAM-related fields in NSH are defined as follows:

      8-bit field defining the IOAM Option-Type, as defined in the "IOAM
      Option-Type" registry specified in [RFC9197].

   IOAM HDR Len:
      8-bit field that contains the length of the IOAM header in
      multiples of 4-octets, including the "IOAM-Type" and "IOAM HDR
      Len" fields.

   Reserved bits:
      Reserved bits are present for future use.  The reserved bits MUST
      be set to 0x0 upon transmission and ignored upon receipt.

   Next Protocol:
      8-bit unsigned integer that determines the type of header
      following IOAM.  The semantics of this field are identical to the
      Next Protocol field in [RFC8300].

   IOAM Option and Optional Data Space:
      IOAM-Data-Fields as specified by the IOAM-Type field.  IOAM-Data-
      Fields are defined corresponding to the IOAM Option-Type (e.g.,
      see Section 4 of [RFC9197] and Section 3.2 of [RFC9326]) and are
      always aligned by 4 octets.  Thus, there is no padding field.

   Multiple IOAM Option-Types MAY be included within the NSH
   encapsulation.  For example, if an NSH encapsulation contains two
   IOAM Option-Types before a data payload, the Next Protocol field of
   the first IOAM option will contain the value 0x06, while the Next
   Protocol field of the second IOAM Option-Type will contain the "NSH
   Next Protocol" number indicating the type of the data payload.  The
   applicability of the IOAM Active and Loopback flags [RFC9322] is
   outside the scope of this document and may be specified in the

   In case the IOAM Incremental Trace Option-Type is used, an SFC-aware
   node that serves as an IOAM transit node needs to adjust the "IOAM
   HDR Len" field accordingly.  See Section 4.4 of [RFC9197].

   Per Section 2.2 of [RFC8300], packets with unsupported Next Protocol
   values SHOULD be silently dropped by default.  Thus, when a packet
   with IOAM is received at an NSH-based forwarding node (such as an
   SFF) that does not support the IOAM header, it SHOULD drop the
   packet.  The mechanisms to maintain and notify of such events are
   outside the scope of this document.

4.  IANA Considerations

   IANA has allocated the following code point for IOAM in the "NSH Next
   Protocol" registry (https://www.iana.org/assignments/nsh):

            | Next Protocol | Description         | Reference |
            | 0x06          | IOAM (Next Protocol | RFC 9452  |
            |               | is an IOAM header)  |           |

                                  Table 1

5.  Security Considerations

   IOAM is considered a "per domain" feature, where the operator decides
   how to leverage and configure IOAM according to the operator's needs.
   The operator needs to properly secure the IOAM domain to avoid
   malicious configuration and use, which could include injecting
   malicious IOAM packets into a domain.  For additional IOAM-related
   security considerations, see Section 9 of [RFC9197].  For additional
   OAM- and NSH-related security considerations, see Section 5 of

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,

   [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,

   [RFC9197]  Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi,
              Ed., "Data Fields for In Situ Operations, Administration,
              and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197,
              May 2022, <https://www.rfc-editor.org/info/rfc9197>.

   [RFC9451]  Boucadair, M., "Operations, Administration, and
              Maintenance (OAM) Packet and Behavior in the Network
              Service Header (NSH)", RFC 9451, DOI 10.17487/RFC9451,
              August 2023, <https://www.rfc-editor.org/info/rfc9451>.

6.2.  Informative References

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,

   [RFC9322]  Mizrahi, T., Brockners, F., Bhandari, S., Gafni, B., and
              M. Spiegel, "In Situ Operations, Administration, and
              Maintenance (IOAM) Loopback and Active Flags", RFC 9322,
              DOI 10.17487/RFC9322, November 2022,

   [RFC9326]  Song, H., Gafni, B., Brockners, F., Bhandari, S., and T.
              Mizrahi, "In Situ Operations, Administration, and
              Maintenance (IOAM) Direct Exporting", RFC 9326,
              DOI 10.17487/RFC9326, November 2022,

   [RFC9378]  Brockners, F., Ed., Bhandari, S., Ed., Bernier, D., and T.
              Mizrahi, Ed., "In Situ Operations, Administration, and
              Maintenance (IOAM) Deployment", RFC 9378,
              DOI 10.17487/RFC9378, April 2023,

Appendix A.  Discussion of the IOAM-Encapsulation Approach

   This section lists several approaches considered for encapsulating
   IOAM with NSH and presents the rationale for the approach chosen in
   this document.

   An encapsulation of IOAM-Data-Fields in NSH should be friendly to an
   implementation in both hardware as well as software forwarders and
   support a wide range of deployment cases, including large networks
   that desire to leverage multiple IOAM-Data-Fields at the same time.

   *  Hardware- and software-friendly implementation:

      Hardware forwarders benefit from an encapsulation that minimizes
      iterative lookups of fields within the packet.  Any operation that
      looks up the value of a field within the packet, based on which
      another lookup is performed, consumes additional gates and time in
      an implementation, both of which should be kept to a minimum.
      This means that flat TLV structures are preferred over nested TLV
      structures.  IOAM-Data-Fields are grouped into several categories,
      including trace, proof-of-transit, and edge-to-edge.  Each of
      these options defines a TLV structure.  A hardware-friendly
      encapsulation approach avoids grouping these three option
      categories into yet another TLV structure and would instead carry
      the options as a serial sequence.

   *  Total length of the IOAM-Data-Fields:

      The total length of IOAM-Data-Fields can grow quite large if
      multiple different IOAM-Data-Fields are used and large path-
      lengths need to be considered.  For example, if an operator would
      consider using the IOAM Trace Option-Type and capture node-id,
      app_data, egress and ingress interface-id, timestamp seconds, and
      timestamp nanoseconds at every hop, then a total of 20 octets
      would be added to the packet at every hop.  In this case, the
      particular deployment has a maximum path length of 15 hops in the
      IOAM domain, and a maximum of 300 octets would be encapsulated in
      the packet.

   Different approaches for encapsulating IOAM-Data-Fields in NSH could
   be considered:

   1.  Encapsulation of IOAM-Data-Fields as "NSH MD Type 2" (see
       [RFC8300], Section 2.5).

       Each IOAM Option-Type (e.g., trace, proof-of-transit, and edge-
       to-edge) would be specified by a type, with the different IOAM-
       Data-Fields being TLVs within this the particular option type.
       NSH MD Type 2 offers support for variable length metadata.  The
       length field is 6 bits, resulting in a maximum of 256 (2^6 x 4)

   2.  Encapsulation of IOAM-Data-Fields using the "Next Protocol"

       Each IOAM Option-Type (e.g., trace, proof-of-transit, and edge-
       to-edge) would be specified by its own "next protocol".

   3.  Encapsulation of IOAM-Data-Fields using the "Next Protocol"

       A single NSH protocol type code point would be allocated for
       IOAM.  A "sub-type" field would then specify what IOAM options
       type (trace, proof-of-transit, edge-to-edge) is carried.

   The third option has been chosen here.  This option avoids the
   additional layer of TLV-nesting that the use of NSH MD Type 2 would
   result in.  In addition, this option does not constrain IOAM data to
   a maximum of 256 octets, thus allowing support for very large


   The authors would like to thank Éric Vyncke, Nalini Elkins, Srihari
   Raghavan, Ranganathan T S, Karthik Babu Harichandra Babu, Akshaya
   Nadahalli, Stefano Previdi, Hemant Singh, Erik Nordmark, LJ Wobker,
   Andrew Yourtchenko, Greg Mirsky, and Mohamed Boucadair for their
   comments and advice.


   The following people contributed significantly to the content of this
   document and should be considered coauthors:

   Vengada Prasad Govindan
   Cisco Systems, Inc.
   Email: venggovi@cisco.com

   Carlos Pignataro
   Cisco Systems, Inc.
   7200-11 Kit Creek Road
   Research Triangle Park, NC 27709
   United States of America
   Email: cpignata@cisco.com

   Hannes Gredler
   RtBrick Inc.
   Email: hannes@rtbrick.com

   John Leddy
   Email: john@leddy.net

   Stephen Youell
   JP Morgan Chase
   25 Bank Street
   E14 5JP
   United Kingdom
   Email: stephen.youell@jpmorgan.com

   Tal Mizrahi
   Huawei Network.IO Innovation Lab
   Email: tal.mizrahi.phd@gmail.com

   David Mozes
   Email: mosesster@gmail.com

   Petr Lapukhov
   1 Hacker Way
   Menlo Park, CA 94025
   United States of America
   Email: petr@fb.com

   Remy Chang
   Barefoot Networks
   2185 Park Boulevard
   Palo Alto, CA 94306
   United States of America

Authors' Addresses

   Frank Brockners (editor)
   Cisco Systems, Inc.
   3rd Floor
   Hansaallee 249
   40549 Duesseldorf
   Email: fbrockne@cisco.com

   Shwetha Bhandari (editor)
   3rd Floor, Indiqube Orion
   24th Main Rd, Garden Layout, HSR Layout
   Bangalore 560 102
   Email: shwetha.bhandari@thoughtspot.com