MPLS Working Group                                        R. Gandhi, Ed.
Internet-Draft                                                    Z. Ali
Updates: 5586 (if approved)                                 F. Brockners
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: 5 August 2022                                            B. Wen
                                                                 Comcast
                                                             B. Decraene
                                                                  Orange
                                                                V. Kozak
                                                                 Comcast
                                                         1 February 2022


           MPLS Data Plane Encapsulation for In-situ OAM Data
                       draft-gandhi-mpls-ioam-03

Abstract

   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 defines how IOAM data fields are transported with MPLS
   data plane encapsulation using new Generic Associated Channel (G-ACh)
   and updates the RFC 5586.

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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on 5 August 2022.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirement Language  . . . . . . . . . . . . . . . . . .   3
     2.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   3
   3.  MPLS Extensions for IOAM Data Fields  . . . . . . . . . . . .   4
     3.1.  IOAM Generic Associated Channel . . . . . . . . . . . . .   4
     3.2.  IOAM Indicators . . . . . . . . . . . . . . . . . . . . .   6
   4.  Edge-to-Edge IOAM . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  IOAM Indicator  . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Procedure for Edge-to-Edge IOAM . . . . . . . . . . . . .   7
   5.  Hop-By-Hop IOAM . . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Hop-By-Hop Indicator  . . . . . . . . . . . . . . . . . .   8
     5.2.  Procedure for Hop-By-Hop IOAM . . . . . . . . . . . . . .   8
   6.  Alternate Method Using MPLS BOS Extension Header with IOAM Data
           Fields  . . . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Considerations for IOAM . . . . . . . . . . . . . . . . . . .  11
     7.1.  Considerations for ECMP . . . . . . . . . . . . . . . . .  11
     7.2.  Node Capability . . . . . . . . . . . . . . . . . . . . .  11
     7.3.  Nested MPLS Encapsulation . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   10. Appendix  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     10.1.  MPLS Encapsulation with Control Word and Another G-ACh for
            IOAM Data Fields . . . . . . . . . . . . . . . . . . . .  12
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     11.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16











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1.  Introduction

   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.
   The term "in-situ" refers to the fact that the IOAM data fields are
   added to the data packets rather than being sent within the probe
   packets specifically dedicated to OAM.  The IOAM data fields are
   defined in [I-D.ietf-ippm-ioam-data].  The IOAM data fields are
   further updated in [I-D.ietf-ippm-ioam-direct-export] for direct
   export use-cases and in [I-D.ietf-ippm-ioam-flags] for Loopback and
   Active flags.

   This document defines how IOAM data fields are transported with MPLS
   data plane encapsulations using new Generic Associated Channel
   (G-ACh) and updates the [RFC5586].

2.  Conventions

2.1.  Requirement Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119] [RFC8174]
   when, and only when, they appear in all capitals, as shown here.

2.2.  Abbreviations

   Abbreviations used in this document:

   IOI  IOAM Indicator


   ECMP  Equal Cost Multi-Path


   E2E  Edge-To-Edge


   EL  Entropy Label


   ELI  Entropy Label Indicator


   ELC  Entropy Label Control





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   G-ACh  Generic Associated Channel


   HBH  Hop-By-Hop


   HBI  Hop-By-Hop Indicator


   IOAM  In-situ Operations, Administration, and Maintenance


   MPLS  Multiprotocol Label Switching


   OAM  Operations, Administration, and Maintenance


   POT  Proof-of-Transit


   PW  PseudoWire


3.  MPLS Extensions for IOAM Data Fields

3.1.  IOAM Generic Associated Channel

   The IOAM header is added containing different IOAM-Data-Fields in the
   MPLS header as shown in Figure 1.  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]).  More than one trace options can
   be present in the IOAM-Data-Fields.

   G-ACh [RFC5586] provides a mechanism to transport OAM and other
   control messages over MPLS data plane.  The IOAM G-ACh header
   [RFC5586] with new IOAM G-ACh type MUST be added immediately after
   the MPLS label stack in the MPLS header as shown in Figure 1, before
   the IOAM-Data-Fields.  The G-ACh label (GAL) [RFC5586] MUST NOT be
   added in the MPLS label stack.

   This document updates the following paragraph in Section 2.1 of
   [RFC5586]: "The G-ACh MUST NOT be used to transport user traffic" to
   "The G-ACh MAY be used with user traffic to transport OAM
   information".





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   Note that the G-ACh is not really used to transport the user traffic
   in this document but to transport the IOAM-Data-Fields with the user
   traffic.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
    |0 0 0 1|Version| Length        |          IOAM G-ACh           |  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |
    | IOAM-OPT-Type | IOAM HDR Len  | Block Number  | Reserved      |  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  I
    |                                                               |  O
    |                                                               |  A
    ~                 IOAM Option and Data Space                    ~  M
    |                                                               |  |
    |                                                               |  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
    |                                                               |
    |                                                               |
    |                 Payload + Padding                             |
    |                                                               |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 1: IOAM Generic Associated Channel with IOAM Data Fields

   The IOAM-Data-Fields are encapsulated using the following fields in
   the MPLS header:

   IP Version Number 0001b:  The first four octets are IP Version Field
     part of a G-ACh header, as defined in [RFC5586].

   Version:  The Version field is set to 0, as defined in [RFC4385].

   Length:  Length of IOAM G-ACh data in 4-octet units.  Note that this
     field is marked as Reserved in [RFC5586] and is updated for the new
     IOAM G-ACh type by this document.

   IOAM G-ACh:  Generic Associated Channel (G-ACh) Type (value TBA1) for
     IOAM [RFC5586].

   Reserved:  Reserved Bits MUST be set to zero upon transmission and
     ignored upon receipt.

   Block Number:  The Block Number can be used to aggregate the IOAM





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     data collected in data plane, e.g. to compute measurement metrics
     for each block of a data flow.  It is also used to correlate the
     IOAM data on different nodes.

   IOAM-OPT-Type:  8-bit field defining the IOAM Option type, as defined
     in the "IOAM Option-Type Registry" specified in
     [I-D.ietf-ippm-ioam-data].

   IOAM HDR Length:  8-bit unsigned integer.  Length of the IOAM Header
     in 4-octet units.

   IOAM Option and Data Space:  IOAM-Data-Fields as specified by the
     IOAM-OPT-Type field.  IOAM-Data-Fields are defined corresponding to
     the IOAM-Option-Type (e.g. see Section 5 of
     [I-D.ietf-ippm-ioam-data] and Section 3.2 of
     [I-D.ietf-ippm-ioam-direct-export].

3.2.  IOAM Indicators

   An IOAM Indicator MUST be used to indicate the presence of the IOAM-
   Data-Fields in the MPLS header.  If both edge and intermediate nodes
   need to process IOAM data then both IOAM Indicator and HBH Indicator
   MUST be used.  The HBH Indicator allows to optimize the IOAM
   processing on intermediate nodes and avoids the need to check all
   IOAM-Data-Fields.

   [RFC6790] defines the MPLS Entropy Label (EL) and Entropy Label
   Indicator (ELI).  [I-D.decraene-mpls-slid-encoded-entropy-label-id]
   defines Entropy Label Control (ELC) field and is carried in the TTL
   field of the Entropy Label.  Additional flags are defined in
   [I-D.jags-mpls-ext-hdr-entropy-lbl].  A flag called IOI (IOAM
   Indicator) in the ELC is defined in this document to indicate the
   presence of IOAM.  A flag called HBI (Hop-By-Hop Indicator) in the
   ELC is defined in [I-D.jags-mpls-ext-hdr-entropy-lbl] to indicate
   that HBH processing is required.  The bit positions of these flags in
   the ELC field can be user-defined, consistently in the network.
   Alternatively, the bit positions of these flag can be allocated by
   IANA.

4.  Edge-to-Edge IOAM

4.1.  IOAM Indicator

   The IOAM Indicator (Flag IOI in the Entropy Label Control field) is
   used to indicate the presence of the IOAM-Data-Fields in the MPLS
   header as shown in Figure 2.





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    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Label(1)                             | TC  |S|  TTL          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Label(n)                             | TC  |S|  TTL          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Entropy Label Indicator (7)          | TC  |0|  TTL          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Entropy Label                        | TC  |1|  ELC (IOI)    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Packet as shown in Figure 1                    |
    .                                                               .
    +---------------------------------------------------------------+

               Figure 2: Example MPLS Encapsulation for IOAM

   The E2E IOAM-Data-Fields carry the Option-Type(s) that require
   processing on the encapsulating and decapsulating nodes only.  The
   IOAM Option-Type carried can be IOAM Edge-to-Edge Option-Type
   [I-D.ietf-ippm-ioam-data].  The E2E IOAM-Data-Fields SHOULD NOT carry
   any IOAM Option-Type that require IOAM processing on the intermediate
   nodes as it will not be processed by them.

4.2.  Procedure for Edge-to-Edge IOAM

   The E2E IOM procedure is summarized as following:

   *  The encapsulating node inserts the ELI, EL pair with the IOAM
      Indicator (Flag IOI) below the label whose FEC is the end
      (decapsulating) node and one or more IOAM-Data-Fields in the MPLS
      header.

   *  The intermediate nodes do not process IOAM-Data-Fields.

   *  The decapsulating node MAY punt a copy of the packet with the
      receive timestamp to the slow path for IOAM-Data-Fields processing
      when the node recognizes the IOAM Indicator.  The receive
      timestamp is required by the various E2E OAM use-cases, including
      streaming telemetry.  Note that the packet is not necessarily
      punted to the control-plane.

   *  The decapsulating node processes the IOAM-Data-Fields using the
      procedures defined in [I-D.ietf-ippm-ioam-data].  An example of
      IOAM processing is to export the IOAM-Data-Fields, send IOAM-Data-
      Fields via streaming telemetry, etc.



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   *  The decapsulating node MUST remove the IOAM-Data-Fields from the
      received packet.  The decapsulated packet is forwarded downstream
      or terminated locally similar to the regular IOAM-Data-Fields.

5.  Hop-By-Hop IOAM

5.1.  Hop-By-Hop Indicator

   The IOAM Indicator (Flag IOI) along with Hop-By-Hop Indicator (Flag
   HBI) in the Entropy Label Control field) are used to indicate the
   presence of the HBH IOAM-Data-Fields in the MPLS header as shown in
   Figure 3.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Label(1)                             | TC  |S|  TTL          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Label(n)                             | TC  |S|  TTL          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Entropy Label Indicator (7)          | TC  |0|  TTL          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Entropy Label                        | TC  |1| ELC(IOI, HBI) |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Packet as shown in Figure 1                    |
    .                                                               .
    +---------------------------------------------------------------+

             Figure 3: Example MPLS Encapsulation for HBH IOAM

   The HBH IOAM-Data-Fields carry the Option-Type(s) that require
   processing at the intermediate and/or encapsulating and decapsulating
   nodes.  The IOAM Option-Type carried can be IOAM Pre-allocated Trace
   Option-Type, IOAM Incremental Trace Option-Type and IOAM Proof of
   Transit (POT) Option-Type, as well as Edge-to-Edge Option-Type
   [I-D.ietf-ippm-ioam-data].

5.2.  Procedure for Hop-By-Hop IOAM

   The HBH IOAM procedure is summarized as following:

   *  The encapsulating node inserts the ELI, EL pair with the IOAM
      Indicator (Flag IOI) and HBH Indicator (Flag HBI) below the label
      whose FEC is the end (decapsulating) node and one or more IOAM-
      Data-Fields in the MPLS header.




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   *  The intermediate node enabled with HBH IOAM function processes the
      data packet including the IOAM-Data-Fields as defined in
      [I-D.ietf-ippm-ioam-data] when the node recognizes the HBH
      Indicator in the MPLS header.

   *  The intermediate node MAY punt a copy of the packet with the
      receive timestamp to the slow path for IOAM-Data-Fields processing
      when the node recognizes the HBH Indicator.  The receive timestamp
      is required by the various HBH OAM use-cases, including streaming
      telemetry.  Note that the packet is not necessarily punted to the
      control-plane.

   *  The intermediate node forwards a copy of the processed data packet
      downstream.

   *  The processing on the decapsulating node is same as E2E case.

6.  Alternate Method Using MPLS BOS Extension Header with IOAM Data
    Fields

   In this method, BOS (Bottom of Stack) Extension Header defined in
   [I-D.jags-mpls-ext-hdr-entropy-lbl] is used with BOS Opcode for IOAM
   (value to be assigned by IANA) as shown in Figure 4 (instead of using
   the G-ACh channel for IOAM defined in this document).

   Flag NH (Next Header Present for BOS Extension Header) and flag H
   (Hop-By-Hop processing required for this BOS Extension Header) as
   defined in [I-D.jags-mpls-ext-hdr-entropy-lbl] are also applicable to
   IOAM BOS Extension Header.






















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    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
    |0 0 1 0|Reserve|BOS Opcode=IOAM|Length (words) | Flags (NH, H) |  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |
    | IOAM-OPT-Type | IOAM HDR Len  | Block Number  | Reserved      |  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  I
    |                                                               |  O
    |                                                               |  A
    ~                 IOAM Option and Data Space                    ~  M
    |                                                               |  |
    |                                                               |  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
    |                                                               |
    |                                                               |
    |                 Payload + Padding                             |
    |                                                               |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 4: IOAM BOS Extended Header with IOAM Data Fields

   Bottom of Stack Presence Indicator (BPI) flag in ELC as defined in
   [I-D.jags-mpls-ext-hdr-entropy-lbl] is set to "1" to indicate the
   presence of the BOS Extension Header (instead of using the IOI flag
   in the ELC defined in this document) as shown in Figure 5.  There is
   no change in the usage of the HBI flag defined in
   [I-D.jags-mpls-ext-hdr-entropy-lbl] and further described in this
   document.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Label(1)                             | TC  |S|  TTL          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Label(n)                             | TC  |S|  TTL          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Entropy Label Indicator (7)          | TC  |0|  TTL          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Entropy Label                        | TC  |1| ELC(BPI, HBI) |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Packet as shown in Figure 4                    |
    .                                                               .
    +---------------------------------------------------------------+




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       Figure 5: Example MPLS Encapsulation for IOAM using BOS Header

7.  Considerations for IOAM

7.1.  Considerations for ECMP

   The encapsulating node needs to make sure the IOAM-Data-Fields do not
   start with a well-known IP Version Number (e.g. 0x4 for IPv4 and 0x6
   for IPv6) as that can alter the hashing function for ECMP that uses
   the IP header.  This is achieved by using the IOAM G-ACh with IP
   Version Number 0001b after the MPLS label stack [RFC5586].

   When entropy label [RFC6790] is used for hashing function for ECMP,
   the procedure defined in this document does not alter the ECMP
   behaviour.

7.2.  Node Capability

   The decapsulating node that has to remove the IOAM-Data-Fields and
   perform the IOAM function may not be capable of supporting it.  The
   encapsulating node needs to know if the decapsulating node can
   support the IOAM function.  The signaling extension for this
   capability exchange is outside the scope of this document.

   The intermediate node that is not capable of supporting the IOAM
   functions defined in this document, can simply skip the IOAM
   processing.

7.3.  Nested MPLS Encapsulation

   The packets with IOAM-Data-Fields may carry one or more Entropy
   Labels with an IOAM Indicator in the MPLS header.  An intermediate
   node that supports IOAM SHOULD check the first Entropy Label in the
   label stack for the IOAM Indicator and the HBH Indicator to process
   the IOAM-Data-Fields.

   An intermediate node that supports IOAM, SHOULD copy the ELC field
   from the received Entropy Label to the new Entropy Label when
   inserting the new Entropy Label in the MPLS header and this can be
   based on a local policy.

   When a packet is received with IOAM, the nested MPLS encapsulating
   node that supports a different IOAM, the node MUST add a new Entropy
   Label with the supported IOAM as part of the new MPLS encapsulation.







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8.  Security Considerations

   The security considerations of IOAM in general are discussed in
   [I-D.ietf-ippm-ioam-data] and apply to the procedure defined in this
   document.

   IOAM is considered a "per domain" feature, where one or several
   operators decide on configuring IOAM according to their needs.  IOAM
   is intended for deployment in limited domains [RFC8799].  As such, it
   assumes that a node involved in IOAM operation has previously
   verified the integrity of the path.  Still, operators need to
   properly secure the IOAM domain to avoid malicious configuration and
   use, which could include injecting malicious IOAM packets into the
   domain.

   Routers that support G-ACh are subject to the same security
   considerations as defined in [RFC4385] and [RFC5586].

9.  IANA Considerations

   IANA maintains G-ACh Type Registry (see
   https://www.iana.org/assignments/g-ach-parameters/g-ach-
   parameters.xhtml).  IANA is requested to allocate a value for IOAM
   G-ACh Type from "MPLS Generalized Associated Channel (G-ACh) Types
   (including Pseudowire Associated Channel Types)" registry.

                +=======+=================+===============+
                | Value | Description     | Reference     |
                +=======+=================+===============+
                | TBA1  | IOAM G-ACh Type | This document |
                +-------+-----------------+---------------+

                          Table 1: IOAM G-ACh Type

10.  Appendix

10.1.  MPLS Encapsulation with Control Word and Another G-ACh for IOAM
       Data Fields

   The IOAM-Data-Fields, including IOAM G-ACh header are added in the
   MPLS encapsulation immediately after the MPLS header.  Any Control
   Word [RFC4385] or another G-ACh [RFC5586] MUST be added after the
   IOAM-Data-Fields in the packet as shown in the Figure 6 and Figure 7,
   respectively.  This allows the intermediate nodes to easily access
   the HBH IOAM-Data-Fields located immediately after the MPLS header.
   The decapsulating node can remove the MPLS encapsulation including
   the IOAM-Data-Fields and then process the Control Word or another
   G-ACh following it.  The subsequent G-ACh and Control Word are



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   located through the use of the "Length" field in the IOAM G-ACh.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Entropy Label Indicator (7)          | TC  |0|  TTL          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Entropy Label                        | TC  |1| ELC(IOI, HBI) |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 1|Version| Length        | IOAM G-ACh                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
    | IOAM-OPT-Type | IOAM HDR Len  | Block Number  | Reserved      |  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  I
    |                                                               |  O
    |                                                               |  A
    ~                 IOAM Option and Data Space                    ~  M
    |                                                               |  |
    |                                                               |  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
    |0 0 0 0| Specified by PW Encapsulation [RFC4385]               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                                                               |
    ~                 Payload + Padding                             ~
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 6: Example MPLS Encapsulation with Generic PW Control Word
                               with HBH IOAM





















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    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Entropy Label Indicator (7)          | TC  |0|  TTL          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Entropy Label                        | TC  |1| ELC(IOI, HBI) |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 1|Version| Length        | IOAM G-ACh                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
    | IOAM-OPT-Type | IOAM HDR Len  | Block Number  | Reserved      |  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  I
    |                                                               |  O
    |                                                               |  A
    ~                 IOAM Option and Data Space                    ~  M
    |                                                               |  |
    |                                                               |  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
    |0 0 0 1|Version| Reserved      | Channel Type                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                                                               |
    ~                 Payload + Padding                             ~
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Figure 7: Example MPLS Encapsulation with Another G-ACh with HBH IOAM

11.  References

11.1.  Normative References

   [I-D.decraene-mpls-slid-encoded-entropy-label-id]
              Decraene, B., Filsfils, C., Henderickx, W., Saad, T.,
              Beeram, V. P., and L. Jalil, "Using Entropy Label for
              Network Slice Identification in MPLS networks.", Work in
              Progress, Internet-Draft, draft-decraene-mpls-slid-
              encoded-entropy-label-id-02, 6 August 2021,
              <https://www.ietf.org/archive/id/draft-decraene-mpls-slid-
              encoded-entropy-label-id-02.txt>.

   [I-D.ietf-ippm-ioam-data]
              Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields
              for In-situ OAM", Work in Progress, Internet-Draft, draft-
              ietf-ippm-ioam-data-17, 13 December 2021,
              <https://www.ietf.org/archive/id/draft-ietf-ippm-ioam-
              data-17.txt>.




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   [I-D.ietf-ippm-ioam-direct-export]
              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, 13 October 2021,
              <https://www.ietf.org/archive/id/draft-ietf-ippm-ioam-
              direct-export-07.txt>.

   [I-D.ietf-ippm-ioam-flags]
              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,
              13 October 2021, <https://www.ietf.org/archive/id/draft-
              ietf-ippm-ioam-flags-07.txt>.

   [I-D.jags-mpls-ext-hdr-entropy-lbl]
              Rajamanickam, J., Gandhi, R., Bhattacharya, J., Decraene,
              B., and R. Zigler, "MPLS Extension Header Encodings Using
              Entropy Label", Work in Progress, Internet-Draft, draft-
              jags-mpls-ext-hdr-entropy-lbl-00, 26 January 2022,
              <https://www.ietf.org/archive/id/draft-jags-mpls-ext-hdr-
              entropy-lbl-00.txt>.

   [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>.

   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
              "MPLS Generic Associated Channel", RFC 5586,
              DOI 10.17487/RFC5586, June 2009,
              <https://www.rfc-editor.org/info/rfc5586>.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, DOI 10.17487/RFC6790, November 2012,
              <https://www.rfc-editor.org/info/rfc6790>.

   [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>.

11.2.  Informative References







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   [RFC4385]  Bryant, S., Swallow, G., Martini, L., and D. McPherson,
              "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
              Use over an MPLS PSN", RFC 4385, DOI 10.17487/RFC4385,
              February 2006, <https://www.rfc-editor.org/info/rfc4385>.

   [RFC8799]  Carpenter, B. and B. Liu, "Limited Domains and Internet
              Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
              <https://www.rfc-editor.org/info/rfc8799>.

Acknowledgements

   The authors would like to thank Patrick Khordoc, Sagar Soni, Shwetha
   Bhandari, Clarence Filsfils, and Vengada Prasad Govindan for the
   discussions on IOAM.  The authors would also like to thank Tarek
   Saad, Loa Andersson, Greg Mirsky, Stewart Bryant, Xiao Min, and Cheng
   Li for providing many useful comments.  The authors would also like
   to thank Mach Chen, Andrew Malis, Matthew Bocci, and Nick Delregno
   for the MPLS-RT reviews.

Authors' Addresses

   Rakesh Gandhi (editor)
   Cisco Systems, Inc.
   Canada

   Email: rgandhi@cisco.com


   Zafar Ali
   Cisco Systems, Inc.

   Email: zali@cisco.com


   Frank Brockners
   Cisco Systems, Inc.
   Hansaallee 249, 3rd Floor
   DUESSELDORF, NORDRHEIN-WESTFALEN 40549
   Germany

   Email: fbrockne@cisco.com


   Bin Wen
   Comcast

   Email: Bin_Wen@cable.comcast.com




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   Bruno Decraene
   Orange

   Email: bruno.decraene@orange.com


   Voitek Kozak
   Comcast

   Email: Voitek_Kozak@comcast.com









































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