Internet-Draft NSH encapsulation for In-situ OAM May 2022
Brockners & Bhandari Expires 19 November 2022 [Page]
Intended Status:
Standards Track
F. Brockners, Ed.
S. Bhandari, Ed.

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 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

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 19 November 2022.

Table of Contents

1. Introduction

In-situ OAM (IOAM), as defined in [I-D.ietf-ippm-ioam-data], 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 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) [RFC8300] encapsulation for the Service Function Chaining (SFC) [RFC7665]. The IOAM-Data-Fields are defined in [I-D.ietf-ippm-ioam-data]. An implementation of IOAM which leverages NSH to carry the IOAM data is available from the open source software project [].

2. Conventions

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.

Abbreviations used in this document:

In-situ Operations, Administration, and Maintenance
Network Service Header
Operations, Administration, and Maintenance
Service Function Chaining
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 which follows the NSH headers. An IOAM header is added containing the different IOAM-Data-Fields. The IOAM-Data-Fields MUST follow the definitions corresponding to IOAM-Option-Types (e.g. see Section 5 of [I-D.ietf-ippm-ioam-data] and Section 3.2 of [I-D.ietf-ippm-ioam-direct-export]). In an administrative domain where IOAM is used, insertion of the IOAM header in NSH is enabled at the NSH tunnel endpoints, which also serve as IOAM encapsulating/decapsulating nodes by means of configuration. There can be multiple IOAM headers added by encapsulating nodes as configured. The IOAM transit nodes (e.g. an SFF) MUST process all the IOAM headers that are relevant based on its configuration. See [I-D.ietf-ippm-ioam-deployment] 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 = TBD_IOAM |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  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/ESP/...)             |
|                                                               |
|                                                               |
|                                                               |

The NSH header and fields are defined in [RFC8300]. The O-bit MUST be handled following the rules in [I-D.ietf-sfc-oam-packet]. The "NSH Next Protocol" value (referred to as "NP" in the diagram above) is TBD_IOAM.

The IOAM related fields in NSH are defined as follows:

Multiple IOAM-Option-Types MAY be included within the NSH encapsulation. For example, if a NSH encapsulation contains two IOAM-Option-Types before a data payload, the Next Protocol field of the first IOAM option will contain the value of TBD_IOAM, 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 [I-D.ietf-ippm-ioam-flags] is outside the scope of this document and may be specified in the future. When a packet with IOAM is received at an NSH based forwarding node such as an Service Function Forwarder (SFF) that does not understand IOAM header, it SHOULD drop the packet. The mechanism to maintain and notify of such events are outside the scope of this document.

4. IANA Considerations

IANA is requested to allocate protocol numbers for the following "NSH Next Protocol" related to IOAM:

              | Next Protocol | Description | Reference     |
              | x             | TBD_IOAM    | This document |

5. Security Considerations

IOAM is considered a "per domain" feature, where one or several operators decide on leveraging and configuring IOAM according to their needs. Still, operators need 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 10 in [I-D.ietf-ippm-ioam-data]. For additional OAM and NSH related security considerations see Section 5 of [I-D.ietf-sfc-oam-packet].

6. Acknowledgements

The authors would like to thank Eric 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 the comments and advice.

7. Contributors

In addition to editors listed on the title page, the following people have contributed to this document:

   Vengada Prasad Govindan
   Cisco Systems, Inc.

   Carlos Pignataro
   Cisco Systems, Inc.
   7200-11 Kit Creek Road
   Research Triangle Park, NC  27709
   United States

   Hannes Gredler
   RtBrick Inc.

   John Leddy

   Stephen Youell
   JP Morgan Chase
   25 Bank Street
   London  E14 5JP
   United Kingdom

   Tal Mizrahi
   Huawei Network.IO Innovation Lab

   David Mozes

   Petr Lapukhov
   1 Hacker Way
   Menlo Park, CA  94025

   Remy Chang
   Barefoot Networks
   2185 Park Boulevard
   Palo Alto, CA  94306

8. References

8.1. Normative References

Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields for In-situ OAM", Work in Progress, Internet-Draft, draft-ietf-ippm-ioam-data-17, , <>.
Boucadair, M., "OAM Packet and Behavior in the Network Service Header (NSH)", Work in Progress, Internet-Draft, draft-ietf-sfc-oam-packet-01, , <>.
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.
Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed., "Network Service Header (NSH)", RFC 8300, DOI 10.17487/RFC8300, , <>.

8.2. Informative References

"Fast Data Project:", <>.
Brockners, F., Bhandari, S., Bernier, D., and T. Mizrahi, "In-situ OAM Deployment", Work in Progress, Internet-Draft, draft-ietf-ippm-ioam-deployment-01, , <>.
Song, H., Gafni, B., Zhou, T., Li, Z., Brockners, F., Bhandari, S., Sivakolundu, R., and T. Mizrahi, "In-situ OAM Direct Exporting", Work in Progress, Internet-Draft, draft-ietf-ippm-ioam-direct-export-07, , <>.
Mizrahi, T., Brockners, F., Bhandari, S., Sivakolundu, R., Pignataro, C., Kfir, A., Gafni, B., Spiegel, M., and J. Lemon, "In-situ OAM Loopback and Active Flags", Work in Progress, Internet-Draft, draft-ietf-ippm-ioam-flags-07, , <>.
Halpern, J., Ed. and C. Pignataro, Ed., "Service Function Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/RFC7665, , <>.

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 look-ups of fields within the packet: Any operation which 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 are desired to be kept to a minimum. This means that flat TLV structures are to be 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, but would rather 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 in case multiple different IOAM-Data-Fields are used and large path-lengths need to be considered. If for example an operator would consider using the IOAM Trace Option-Type and capture node-id, app_data, egress/ingress interface-id, timestamp seconds, timestamps nanoseconds at every hop, then a total of 20 octets would be added to the packet at every hop. In case this particular deployment would have a maximum path length of 15 hops in the IOAM domain, then a maximum of 300 octets were to 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 meta-data. The length field is 6-bits, resulting in a maximum of 256 (2^6 x 4) octets.
  2. Encapsulation of IOAM-Data-Fields using the "Next Protocol" field. 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" field. 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 deployments.

Authors' Addresses

Frank Brockners (editor)
Cisco Systems, Inc.
Hansaallee 249, 3rd Floor
Shwetha Bhandari (editor)
3rd Floor, Indiqube Orion, 24th Main Rd, Garden Layout, HSR Layout
Bangalore, KARNATAKA 560 102