Internet-Draft IOAM Using MPLS Network Actions August 2026
Gandhi, et al. Expires 12 February 2027 [Page]
Workgroup:
MPLS Working Group
Internet-Draft:
draft-ietf-mpls-mna-ioam-10
Published:
Intended Status:
Standards Track
Expires:
Authors:
R. Gandhi, Ed.
Cisco Systems, Inc.
G. Mirsky, Ed.
Individual
H. Song
Futurewei Technologies
B. Wen
Comcast
V. Kozak
Comcast

Supporting In Situ Operations, Administration, and Maintenance Using MPLS Network Actions

Abstract

In situ Operations, Administration, and Maintenance (IOAM), defined in RFC 9197, collects operational and telemetry information in the packet using IOAM-Data-Fields while the packet traverses a path between two points in the network. Several IOAM Option-Types are available, for example, Pre-allocated Trace, Proof-of-Transit (POT), Edge-to-Edge (E2E), and Incremental Trace, that can be used to collect information for calculating various performance metrics.

RFC 9326 defines the IOAM Direct Export (IOAM-DEX) Option-Type in which the operational state and telemetry information are collected according to the specified profile and exported in a manner and format defined by a local policy on each node along the path.

MPLS Network Actions (MNA) techniques indicate actions to be performed on any combination of Label Switched Paths, MPLS packets, and the node itself, and to transport data needed for these actions. This document employs the MNA mechanisms to collect and transport the operational state and telemetry information using IOAM-Data-Fields as well as IOAM-DEX.

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 12 February 2027.

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Table of Contents

1. Introduction

In situ Operations, Administration, and Maintenance (IOAM) [RFC9197] collects operational and telemetry information in the packet using IOAM-Data-Fields while the packet traverses a path between two points in the network. Several IOAM Option-Types are available, for example, Pre-allocated Trace, Proof-of-Transit (POT), Edge-to-Edge (E2E), and Incremental Trace, that can be used to collect information for calculating various performance metrics. Such mechanisms transport the collected information from an IOAM encapsulating node to an IOAM decapsulating node (both typically located at the edge of the IOAM domain within the data path).

IOAM Direct Export (IOAM-DEX) [RFC9326] is an IOAM Option-Type in which the operational state and telemetry information are collected according to the specified profile and exported in a manner and format defined by a local policy on each node along the path.

MPLS Network Actions (MNA) techniques [RFC9789] indicate actions to be performed on any combination of Label Switched Paths, MPLS packets, and the node itself, and allow for the transport of data needed for these actions. [RFC9994] defines mechanisms for carrying a Network Action Sub-Stack (NAS) as part of the MPLS label stack, i.e., the In-Stack MNA solution. [I-D.ietf-mpls-mna-ps-hdr] defines mechanisms for carrying MNA and Ancillary Data (AD) below the MPLS label stack, i.e., as the Post-Stack MNA solution. [RFC9791] describes various use cases that can be realized using the MNA solution, including the IOAM and IOAM-DEX.

This document employs the MNA mechanisms to collect and transport the operational state and telemetry information using IOAM Option-Types, including Pre-allocated Trace, POT, and E2E, as well as IOAM-DEX. The mechanism for exporting the collected information for the IOAM-DEX Option-Type is outside the scope of this document. Also, support for the Incremental Trace IOAM Option-Type is outside the scope of this document.

2. Conventions Used in This Document

2.1. Acronyms

The terminology defined in [RFC9789], [RFC9994], and [I-D.ietf-mpls-mna-ps-hdr] is used in this document.

Table 1: Acronyms
Abbreviation Meaning Reference
AD Ancillary Data [I-D.ietf-mpls-mna-ps-hdr]
BoS Bottom of Stack [RFC3032]
HbH Hop-by-Hop [RFC9789]
I2E Ingress to Egress [RFC9789]
E2E Edge-to-Edge [RFC9197]
IHS I2E, HbH, or Select [RFC9994]
IOAM In situ Operations, Administration, and Maintenance [RFC9197]
IOAM-DEX IOAM Direct Export [RFC9326]
IOAM-DEX-MNA-ISD IOAM Direct Export as MPLS Network Action ISD This document
ISD In-Stack Data [RFC9613]
LSE Label Stack Entry [RFC9789]
MNA MPLS Network Action [RFC9789]
MPLS Multiprotocol Label Switching [RFC3032]
NAI Network Action Indicator [RFC9613]
NAL Network Action Length [RFC9994]
NAS Network Action Sub-Stack [RFC9789]
NASL Network Action Sub-Stack Length [RFC9994]
OAM Operations, Administration, and Maintenance [RFC6291]
P bit Post-Stack Data Presence bit [I-D.ietf-mpls-mna-ps-hdr]
POT Proof-of-Transit [RFC9197]
RLD Readable Label Depth [RFC9789]
PFN Post-Stack First Nibble [I-D.ietf-mpls-mna-ps-hdr]
PSD Post-Stack Data [I-D.ietf-mpls-mna-ps-hdr]
PSMH Post-Stack MPLS Header [I-D.ietf-mpls-mna-ps-hdr]
S bit Bottom of Stack bit [RFC3032]
TC Traffic Class [RFC5462]
TTL Time to Live [RFC3032]
U bit Unknown Network Action Handling bit [RFC9994]

2.2. Requirements Language

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.

3. Applicability of IOAM and IOAM-DEX in an MPLS Network

Pre-allocated Trace, POT, and E2E IOAM Option-Types [RFC9197] use user packets to collect and transport the operational state and telemetry information. This document defines the Post-Stack MNA [I-D.ietf-mpls-mna-ps-hdr] solution supporting Pre-allocated Trace, POT, and E2E IOAM Option-Types (Section 4.1).

However, for some use cases, e.g., mobile backhaul, in which network resources are closely controlled, collecting and transporting telemetry information within a user packet may noticeably reduce the cost efficiency of network operations. As such, collecting and transporting the operational state and telemetry information using the management plane is a viable option for some environments. IOAM-DEX [RFC9326] allows collecting the IOAM-Data-Fields defined in [RFC9197] using on-path telemetry information. In this document, the In-Stack and Post-Stack realizations of IOAM-DEX are specified in Section 4.2 and Section 4.1, respectively.

The procedure defined in this document for carrying IOAM Option-Types using the MNA solution can be applied to user traffic packets and active measurement test packets. [I-D.gandhi-ippm-stamp-mpls-hdr] uses the mechanisms defined in this document to transport IOAM Option-Types using the MNA solution, with Simple Two-Way Active Measurement Protocol (STAMP) test packets for Hop-by-Hop (HbH) and E2E measurements. [I-D.ietf-ippm-on-path-active-measurements] also describes active measurement methods where the mechanisms defined in this document can carry IOAM Option-Types for on-path telemetry in MPLS networks using MNA.

4. Realization of IOAM and IOAM-DEX as MPLS Network Actions

4.1. Realization of IOAM and IOAM-DEX as Post-Stack MNA

The presence of a corresponding Post-Stack MPLS Header (PSMH) is indicated using the P bit in the NAS as defined in [I-D.ietf-mpls-mna-ps-hdr]. An example of a NAS and the corresponding PSMH carrying IOAM and IOAM-DEX Option-Types is shown in Figure 1.

  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                MNA Label (value 4)    | TC  |S|  TTL          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Opcode     |  13-bit Data (Format B) |P|IHS|S|  NASL |U| NAL |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                Label                  | TC  |1|  TTL          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~ Post-Stack MPLS Header for IOAM and IOAM-DEX per Figure 2     ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                Optional Payload + Padding                     ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: An Example of In-Stack Network Action Sub-Stack for Post-Stack MPLS Header Carrying IOAM and IOAM-DEX

The MNA Label (value 4) is defined in [RFC9994].

S (1-bit): The BoS [RFC3032].

P (1-bit): The P bit is set as specified in [I-D.ietf-mpls-mna-ps-hdr].

The NAL and NASL fields are set as specified in [RFC9994].

Opcode (7-bit): The opcode is set as specified in [RFC9994].

The Data (13-bit, next to the Opcode field): The data is set as specified in [RFC9994].

The U bit is set as specified in [RFC9994] for In-Stack Network Actions and updated in [I-D.ietf-mpls-mna-ps-hdr] for Post-Stack Network Actions.

The IHS scope field is set as defined in [RFC9994] and updated in [I-D.ietf-mpls-mna-ps-hdr] to indicate that I2E, HbH, or Select processing scope for the Post-Stack Network Action and the associated Post-Stack Data when the P bit is set.

If both edge and intermediate nodes need to process the IOAM Option-Types, then the IHS scope MUST be set to "HbH, value 0x1". If only edge nodes need to process the IOAM Option-Types, then the IHS scope MUST be set to "I2E, value 0x0". The I2E scope allows skipping IOAM processing on the intermediate nodes, i.e., it avoids the need to parse all IOAM Option-Types to detect the one that requires HbH processing.

4.1.1. MPLS Network Action Post-Stack MPLS Header for IOAM and IOAM-DEX

An example encoding of PSMH carrying IOAM and IOAM-DEX in Post-Stack Data (PSD) is shown in Figure 2.

  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  PFN  |Reserve|  PSMH-Len     | Type = MNA Post-Stack Header  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  MNA-PS-OP  |R|R|   PS-NAL    | Block-Number  |R|IOAM-Opt-Type|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~       IOAM Option-Type and Data Space [RFC9197] [RFC9326]     ~
 ~       Beginning from Namespace-ID                             ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: An Example of Post-Stack MPLS Header Carrying IOAM and IOAM-DEX

The Post-Stack MPLS Base Header is added and contains the following fields as defined in [I-D.ietf-mpls-mna-ps-hdr].

PFN (4-bit):
The Post-Stack First Nibble (PFN) (value 0x0) as defined in [I-D.ietf-mpls-mna-ps-hdr].
PSMH-Len (8-bit):
The PSMH total length is set as defined in [I-D.ietf-mpls-mna-ps-hdr].
Type (16-bit):
Type for MNA Post-Stack Header (value 1) as defined in [I-D.ietf-mpls-mna-ps-hdr].

The PSMH is added after the Post-Stack MPLS Base Header and contains the Post-Stack Network Action Opcode for IOAM and IOAM-DEX, the length in 4-octet units, and the IOAM Option-Type with IOAM-Data-Fields in the Post-Stack ancillary data as shown in Figure 2. The IOAM-Data-Fields MUST follow the definitions corresponding to their IOAM Option-Types (e.g., see Section 4 of [RFC9197] and the IOAM-DEX Option-Type in Section 3 of [RFC9326]).

An IOAM Option-Type is added to the PSMH and contains the following fields:

MNA-PS-OP (7-bit):
Set to Opcode TBA1 (Network Action Opcode for IOAM and IOAM-DEX in PSD) for the IOAM Option-Type defined in [RFC9197], and the IOAM-DEX Option-Type defined in [RFC9326].
IOAM-Opt-Type (7-bit):
The field to carry the IOAM Option-Type, as defined in the "IOAM Option-Type Registry" in [RFC9197] and [RFC9326].
PS-NAL (7-bit):
Unsigned integer representing the length of the IOAM-Data-Fields in 4-octet units for the MNA-PS-OP. This excludes the first 4-octet unit.
IOAM Option-Type and Data Space:
IOAM-Data-Fields as specified by the IOAM-Opt-Type field, beginning from the Namespace-ID field. IOAM-Data-Fields are defined according to the IOAM Option-Type (e.g., see Section 4 of [RFC9197] and Section 3 of [RFC9326]).
Block-Number (8-bit):
The Block-Number is used for the alternate marking method [RFC9341] to aggregate the IOAM-Data-Fields collected in the data plane and to correlate IOAM-Data-Fields exported from different nodes along the packet path, e.g., to compute measurement metrics for each block of a data flow. When the Flow ID field is present, the Block-Number is scoped per data flow within the IOAM Namespace identified by the Namespace-ID field. When the Flow ID field is absent, the Block-Number is scoped per IOAM Namespace (identified by the Namespace-ID field) and applies to all flows sharing that Namespace. The Block-Number is incremented sequentially at every measurement interval provisioned on the encapsulating node. When the alternate marking method is not used, the Block-Number SHOULD be set to 0.
4.1.1.1. Multiple IOAM and IOAM-DEX Option-Types in PSMH

An example of multiple Post-Stack Network Actions with the same scope carrying different IOAM Option-Types is 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  PFN  |Reserve|  PSMH-Len     | Type = MNA Post-Stack Header  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  MNA-PS-OP  |R|R|   PS-NAL    | Block-Number  |R|IOAM-Opt-Type|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~  IOAM Option-Type and Data Space [RFC9197] [RFC9326]          ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 .                                                               .
 .                                                               .
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  MNA-PS-OP  |R|R|   PS-NAL    | Block-Number  |R|IOAM-Opt-Type|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~  IOAM Option-Type and Data Space [RFC9197] [RFC9326]          ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                 Optional Payload + Padding                    ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Example of Multiple Post-Stack Network Actions with IOAM and IOAM-DEX with the Same Scope

4.2. Realization of IOAM-DEX as In-Stack MNA

This document adopts the IOAM-DEX Option-Type format defined in [RFC9326] to support IOAM-DEX in an MPLS network using MNA In-Stack Data (ISD) [RFC9994].

To support the direct export of the operational state and telemetry information, the IOAM-DEX-MNA-ISD Binary Large OBject (blob) is placed as part of the ISD block in an MPLS label stack according to the MNA encoding procedures defined in [RFC9994].

Using the IHS field, the IOAM-DEX-MNA-ISD can operate in HbH, I2E, or Select modes [RFC9789] to collect the operational state and telemetry information using an MNA Opcode (Figure 4).

  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                MNA Label (value 4)    | TC  |S|    TTL        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |Opcode = TBA2|  13-bit Data (Format B) |P|IHS|S|  NASL |U| NAL |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~1|     IOAM-DEX-MNA-ISD per Figure 5         |S|               ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: An Example of IOAM-DEX Encapsulation as an MNA Opcode

Here, the enclosed elements are defined as follows:

  • The MNA Label (value 4) is defined in [RFC9994].
  • S (1-bit): The BoS [RFC3032].
  • P (1-bit): The P bit is set as specified in [I-D.ietf-mpls-mna-ps-hdr].
  • The IHS, U bit, and NAL fields are set as specified in [RFC9994].
  • NASL (4-bit): The number of LSEs that compose the IOAM-DEX-MNA-ISD blob.
  • Opcode (7-bit): Set to TBA2 for the Network Action Opcode for IOAM-DEX in ISD.
  • Data: Data field is not used and MUST be set to 0.
  • IOAM-DEX-MNA-ISD: IOAM-DEX in MPLS Network Action ISD encoding.

Policies controlling the processing of the collected operational state and telemetry information, and their transport, are outside the scope of this document.

4.2.1. IOAM-DEX Option-Type Encoding as MNA ISD

The IOAM-DEX-MNA-ISD blob in a NAS uses the LSE Format D, as defined in Section 4.4 of [RFC9994], that maps to the IOAM-DEX Option-Type format [RFC9326]. In addition to the requirement to preserve the S bit, the most significant bit in LSE Format D is always set to 1, avoiding a possible mix-up of the LSE with one of the Base Special Purpose Labels [RFC9994]. The format of the IOAM-DEX-MNA-ISD blob in an NAS is shown in Figure 5.

  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |1|         Namespace-ID          | Reserved  |S|     Flags     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |1|         IOAM-Trace-Type-MNA               |S|O|R| Ext-Flags |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |1|         Flow ID MNA (Optional)            |S|  Flow ID MNA  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |1|         Sequence Number MNA (Optional)    |S|  Seq Num MNA  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: IOAM-DEX Option-Type Format for MPLS Network Action ISD

Where fields are defined as follows:

  • Namespace-ID (16-bit): Identifier of the IOAM Namespace, as defined in Section 3.2 of [RFC9326].
  • Reserved (6-bit): The Reserved field MUST be set to 0 on transmit and ignored on receipt.
  • Flags (8-bit): The flags field comprises eight one-bit subfields. The subfields in the Flags field is allocated by IANA in the IOAM-DEX Flags registry, as defined in Section 4.2 of [RFC9326].
  • IOAM-Trace-Type-MNA (22-bit): The IOAM-Trace-Type-MNA corresponds to the IOAM-Trace-Type field defined in Section 3.2 of [RFC9326]. The interpretation of bit positions, from bit 0 through bit 21, is as specified in [RFC9197]. Note that bits as specified in [RFC9197] are right-shifted one bit, so for example, bit 0 in [RFC9197] (leftmost bit for hop_Lim and node_id in short format) is mapped to bit 1 (second leftmost bit) in the MNA encoding. The registry that contains the assigned code points is found in IANA's IOAM Trace-Type registry [IANA-IOAM-Trace-Type].
  • O: This is a one-bit flag identical to the interpretation of bit 22 of the IOAM-Trace-Type field as defined in Section 3.2 of [RFC9326], marked as "variable-length Opaque State Snapshot" per [RFC9197]; assigned code points are found in IANA's IOAM Trace-Type registry [IANA-IOAM-Trace-Type].
  • R: This is a one-bit flag identical to the interpretation of bit 23 of the IOAM-Trace-Type field as defined in Section 3.2 of [RFC9326], marked as "reserved" per [RFC9197]; assigned code points are found in IANA's IOAM Trace-Type registry [IANA-IOAM-Trace-Type]. Similarly to [RFC9326], the R bit is reserved to allow for future extensions of the IOAM-Trace-Type-MNA bit field, i.e., it indicates the presence of the extended IOAM-Trace-Type-MNA field in the next LSE in Format D.
  • The concatenation of the 22-bit IOAM-Trace-Type-MNA field with O and R flags, explained above, is identical to the 24-bit IOAM-Trace-Type field in Section 3.2 of [RFC9326], and in the interpretation of those bits as defined in [RFC9197] and assigned code points found in IANA's IOAM Trace-Type registry [IANA-IOAM-Trace-Type].
  • Ext-Flags (6-bit): This field comprises six one-bit subfields. The allocation of the subfields in the Ext-Flags field are according to Section 4.3 of [RFC9326]. Four flags have been assigned by IANA: two as defined in Section 4.3 of [RFC9326] indicating the presence of the optional Flow ID MNA and Sequence Number MNA fields, and two as defined in Section 4.1 of [RFC9630] indicating the presence of the optional Multicast Branch ID field. The length of the Ext-Flags field in the IOAM-DEX Option-Type in MNA is shorter by two one-bit fields compared to the length of the Extension Flags field defined in Section 3.2 of [RFC9326]. In the 6-bit Ext-Flags field of the IOAM-DEX-MNA-ISD header, four flags have been mapped to those IANA assigned flags in the IOAM-DEX Option-Type, and two flags remain unmapped. Figure 6 displays the detailed format of the Ext-Flags field.
  • According to Section 3.2 in [RFC9326], the Reserved field is used to align optional fields at the 4-octet word boundary in IOAM-DEX Option-Type. In the case of the IOAM-DEX in MNA, for optional fields such as Flow ID MNA and Sequence Number MNA, such alignment is achieved without adding such Reserved field as padding.
  • Flow ID MNA: An optional 4-octet field containing a 30-bit Flow ID (after removing leading 1 and S bits). The semantics of the Flow ID MNA field are as those of the Flow ID field defined in Section 3.2 of [RFC9326]. The most significant bit MUST be set to 1. The bit 23 MUST be set according to the definition of the S bit in [RFC3032].
  • Sequence Number MNA: An optional 4-octet field containing a 30-bit sequence number (after removing leading 1 and S bits). The semantics of the Sequence Number MNA field are as those of the Sequence Number field defined in Section 3.2 of [RFC9326]. The most significant bit MUST be set to 1. The bit 23 MUST be set according to the definition of the S bit in [RFC3032]. In MPLS network environments where label stack information is used for load-balancing flows, the 19-bit-long part of the Sequence Number MNA, starting from the bit 1 position of the LSE, MUST remain immutable for a particular packet flow that the value of the Flow ID MNA field identifies. In MPLS networks, where other load-balancing techniques are used, all bits of the Sequence Number MNA field can be varied. 
                          0 1 2 3 4 5
                         +-+-+-+-+-+-+
                         |F|Q|N|I|U|U|
                         +-+-+-+-+-+-+
Figure 6: Ext-Flags Field Format

Where fields are defined as follows:

  • F: One-bit flag. When the F flag is set to 1, it indicates the presence of the Flow ID field in the IOAM-DEX-MNA-ISD header.
  • Q: One-bit flag. When the Q flag is set to 1, it indicates the presence of the Sequence Number field in the IOAM-DEX-MNA-ISD header. The designation as Q flag is used to avoid conflicting with the existing S bit for Bottom-of-Stack (BoS) in the MPLS header.
  • N: One-bit flag. When the N flag is set to 1, it indicates the presence of the Multicast Branching Node ID in the Multicast Branch ID field, as defined in Section 4.1 of [RFC9630].
  • I: One-bit flag. When the I flag is set to 1, it indicates the presence of the Multicast Branching Interface Index in the Multicast Branch ID field, as defined in Section 4.1 of [RFC9630]. The N and I flags MUST be both set or both cleared; otherwise the header is considered malformed and the packet MUST be dropped.
  • U: Unassigned one-bit flag. It MUST be set to zero on transmission and the value MUST be ignored upon receipt.

5. Considerations for IOAM and IOAM-DEX in MPLS Networks

5.1. Ingress-to-Egress Scope IOAM and IOAM-DEX Network Actions

The Network Actions with I2E scope carry IOAM Option-Types that require processing on the encapsulating and egress nodes only.

The IOAM Option-Type carried can be the IOAM E2E Option-Type (value 3) defined in [RFC9197] or the IOAM-DEX Option-Type (value 4) defined in [RFC9326]. The Network Actions with I2E scope SHOULD NOT carry any IOAM Option-Type that requires IOAM processing on the intermediate nodes, as it will not be processed by them when the IHS scope is set to "I2E, value 0x0".

The IOAM and IOAM-DEX Network Action procedure with I2E scope is summarized as follows:

  • The encapsulating node inserts a NAS with the IHS scope set to "I2E, value 0x0", as well as one or more Network Actions for IOAM and IOAM-DEX in the MPLS packet.
  • The intermediate nodes do not process the IOAM Option-Types carried with I2E scope.
  • The egress node processes the IOAM-Data-Fields using the procedures defined in [RFC9197] and [RFC9326]. An example of IOAM processing is to export the IOAM-Data-Fields for streaming telemetry.
  • The egress node MUST remove the Network Actions and IOAM-Data-Fields from the received packet. The decapsulated packet is forwarded downstream similar to the regular data packets or terminated locally.

5.2. Hop-by-Hop Scope IOAM and IOAM-DEX Network Actions

The Network Actions with HbH scope carry IOAM Option-Types that require processing at the intermediate and/or encapsulating and egress nodes.

The IOAM Option-Type carried can be Pre-allocated Trace (value 0), POT (value 2), or E2E (value 3) defined in [RFC9197], or IOAM-DEX (value 4) defined in [RFC9326].

Note that the MPLS Network Action defined in this document is not supported for the IOAM Incremental Trace Option-Type (value 1), which requires HbH processing.

The IOAM and IOAM-DEX Network Action procedure with HbH scope is summarized as follows:

  • The encapsulating node inserts a NAS with the IHS scope set to "HbH, value 0x1", as well as one or more Network Actions for IOAM and IOAM-DEX in the MPLS packet.
  • The intermediate node that is enabled for the IOAM function processes the IOAM-Data-Fields as defined in [RFC9197] and [RFC9326] when the node recognizes the HbH scope in the NAS.
  • The intermediate node forwards the data packet downstream.
  • The processing on the egress node is the same as in the I2E case.

Both HbH and I2E scope Network Actions for IOAM and IOAM-DEX may be carried in the Post-Stack MNA in an MPLS packet. In this case, the PSMH carrying HbH-scoped Network Actions MUST be added after the BoS and before the PSMH carrying I2E-scoped Network Actions. This minimizes the Readable Label Depth (RLD) required for intermediate node processing.

5.3. Node Capability

The egress node that needs to remove the IOAM-Data-Fields and IOAM-DEX data and perform the IOAM and IOAM-DEX functions may not be capable of supporting them. The encapsulating node needs to know if the egress node can support the IOAM and IOAM-DEX functions. 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 and IOAM-DEX functions defined in this document can simply skip the IOAM and IOAM-DEX processing.

5.4. Nested MPLS Encapsulation

When a packet is received with an MPLS-encapsulated Network Action for IOAM and IOAM-DEX, and the nested MPLS encapsulating node needs to add a different Network Action for IOAM and IOAM-DEX, the node MUST add a new NAS and the corresponding PSMH with the Network Action for IOAM and IOAM-DEX as part of the new MPLS encapsulation.

5.5. Readable Label Depth Consideration

The encapsulating node needs to ensure that the IOAM-Data-Fields and IOAM-DEX data in a NAS and the associated PSMH are added within the RLD of the downstream MNA-capable nodes so that they can process the IOAM-Data-Fields and IOAM-DEX data.

6. Operational Considerations

Operational considerations discussed in [RFC9994] and [I-D.ietf-mpls-mna-ps-hdr], management considerations discussed in [RFC9789], and management and deployment considerations discussed in [RFC9197] apply to this document. The performance considerations discussed in Section 5 of [RFC9326] are also applicable here.

Additional operational considerations are described in Section 5 for deploying IOAM and IOAM-DEX in MPLS networks.

Policies controlling the processing of the collected operational state and telemetry information, and their transport, are outside the scope of this document.

7. Security Considerations

Security considerations discussed in [RFC9197], [RFC9326], [RFC9789], [RFC9994], and [I-D.ietf-mpls-mna-ps-hdr] apply to this document.

The usage of MPLS Network Actions defined in this document for IOAM and IOAM-DEX is intended for deployment in a single network administrative domain. As such, it assumes that the operator enabling the IOAM and IOAM-DEX operations has previously verified the integrity of the path. However, operators need to properly secure the IOAM and IOAM-DEX in the domain to avoid malicious configuration and use, which could include injecting malicious IOAM and IOAM-DEX packets into the domain.

8. IANA Considerations

8.1. MPLS Network Action Opcodes

IANA is requested to assign code points from its Network Action Opcodes registry (created in [RFC9994] and updated in [I-D.ietf-mpls-mna-ps-hdr]) as specified in Table 2.

Table 2: MPLS Network Action Opcodes
Opcode Description In-Stack Only, Post-Stack Only, In-Stack and Post-Stack Reference
TBA1 Network Action for IOAM and IOAM-DEX in PSD Post-Stack Only This document
TBA2 Network Action for IOAM-DEX in ISD In-Stack Only This document

9. References

9.1. Normative References

[I-D.ietf-mpls-mna-ps-hdr]
Rajamanickam, J., Gandhi, R., Zigler, R., Dong, J., and J. Bhattacharya, "MPLS Network Action (MNA) Post-Stack Header Specification", Work in Progress, Internet-Draft, draft-ietf-mpls-mna-ps-hdr-19, , <https://datatracker.ietf.org/doc/html/draft-ietf-mpls-mna-ps-hdr-19>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC3032]
Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC 3032, DOI 10.17487/RFC3032, , <https://www.rfc-editor.org/info/rfc3032>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.
[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, , <https://www.rfc-editor.org/info/rfc9197>.
[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, , <https://www.rfc-editor.org/info/rfc9326>.
[RFC9341]
Fioccola, G., Ed., Cociglio, M., Mirsky, G., Mizrahi, T., and T. Zhou, "Alternate-Marking Method", RFC 9341, DOI 10.17487/RFC9341, , <https://www.rfc-editor.org/info/rfc9341>.
[RFC9630]
Song, H., McBride, M., Mirsky, G., Mishra, G., Asaeda, H., and T. Zhou, "Multicast On-Path Telemetry Using In Situ Operations, Administration, and Maintenance (IOAM)", RFC 9630, DOI 10.17487/RFC9630, , <https://www.rfc-editor.org/info/rfc9630>.
[RFC9789]
Andersson, L., Bryant, S., Bocci, M., and T. Li, "MPLS Network Actions (MNAs) Framework", RFC 9789, DOI 10.17487/RFC9789, , <https://www.rfc-editor.org/info/rfc9789>.
[RFC9994]
Rajamanickam, J., Ed., Gandhi, R., Ed., Zigler, R., Song, H., and K. Kompella, "MPLS Network Action (MNA) Sub-Stack Specification Including In-Stack Network Actions and Data", RFC 9994, DOI 10.17487/RFC9994, , <https://www.rfc-editor.org/info/rfc9994>.

9.2. Informative References

[I-D.gandhi-ippm-stamp-mpls-hdr]
Gandhi, R., Zhou, T., Li, Z., Ihle, F., and B. Wen, "Simple Two-Way Active Measurement Protocol (STAMP) Extensions for Reflecting STAMP Packet MPLS Network Action Headers", Work in Progress, Internet-Draft, draft-gandhi-ippm-stamp-mpls-hdr-08, , <https://datatracker.ietf.org/doc/html/draft-gandhi-ippm-stamp-mpls-hdr-08>.
[I-D.ietf-ippm-on-path-active-measurements]
Fioccola, G., Zhu, K., Zhou, T., Zhu, Y., and X. Min, "On-Path Telemetry for Active Performance Measurements", Work in Progress, Internet-Draft, draft-ietf-ippm-on-path-active-measurements-02, , <https://datatracker.ietf.org/doc/html/draft-ietf-ippm-on-path-active-measurements-02>.
[IANA-IOAM-Trace-Type]
IANA, "IOAM Trace-Type", <https://www.iana.org/assignments/ioam/ioam.xhtml#trace-type>.
[RFC5462]
Andersson, L. and R. Asati, "Multiprotocol Label Switching (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic Class" Field", RFC 5462, DOI 10.17487/RFC5462, , <https://www.rfc-editor.org/info/rfc5462>.
[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, , <https://www.rfc-editor.org/info/rfc6291>.
[RFC9613]
Bocci, M., Ed., Bryant, S., and J. Drake, "Requirements for Solutions that Support MPLS Network Actions (MNAs)", RFC 9613, DOI 10.17487/RFC9613, , <https://www.rfc-editor.org/info/rfc9613>.
[RFC9791]
Saad, T., Makhijani, K., Song, H., and G. Mirsky, "Use Cases for MPLS Network Action Indicators and Ancillary Data", RFC 9791, DOI 10.17487/RFC9791, , <https://www.rfc-editor.org/info/rfc9791>.

Appendix A: Examples

Example 1: In-Stack and Post-Stack Network Action Processing Order

The PSMH Start Offset Network Action can be added to interleave Post-Stack Network Actions with In-Stack Network Actions. The following example shows how to process the Post-Stack Network Action before some of the In-Stack Network Actions.

  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           MNA Label (value 4)         | TC  |0|    TTL        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Opcode=L    |      Ancillary Data     |1|IHS|0| NASL=3|U|NAL=0|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Opcode=1    |      Flag-Based NAIs          |0| NAIs  |U|NAL=0|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Opcode=TBA3 |      0                        |0|  0    |U|NAL=0|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Opcode=M    |      Ancillary Data           |1|  AD   |U|NAL=0|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | PFN   |Reserve|    PSMH-Len   | Type = MNA Post-Stack Header  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |Opcode = TBA1|R|R|   PS-NAL    | Block-Number  |R|IOAM-Opt-Type|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~       IOAM Option-Type and Data Space [RFC9197] [RFC9326]     ~
 ~       Beginning from Namespace-ID                             ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Example of Post-Stack and In-Stack Network Action Processing Order

In this example, shown in Figure 7, opcode L is processed first, followed by opcode 1 for Flag-Based NAIs, then opcode TBA3 (PSMH Start Offset defined in [I-D.ietf-mpls-mna-ps-hdr]), and the opcode TBA1 in the corresponding PSMH, and finally opcode M.

The network action allocation for Opcode L and Opcode M is outside the scope of this document.

Acknowledgments

The authors would like to thank Adrian Farrel and Xueyan Song for reviewing this document and providing review comments. The authors would also like to thank Patrick Khordoc, Sagar Soni, Shwetha Bhandari, Vengada Prasad Govindan, Tarek Saad, Stewart Bryant, Xiao Min, Jaganbabu Rajamanickam, and Cheng Li for reviewing the early version of this document. The authors would also like to thank Mach Chen, Andrew Malis, Matthew Bocci, and Nick Delregno for the MPLS-RT expert review of the early version of this document. The authors also thank Giuseppe Fioccola for the PerfMetrDir review, which helped improve this document.

Contributors

The following people have substantially contributed to this document:


Zafar Ali
Cisco Systems, Inc.
Email: zali@cisco.com

Frank Brockners
Cisco Systems, Inc.
Germany
Email: fbrockne@cisco.com

Loa Andersson
Huawei Technologies
Email: loa@pi.nu

Authors' Addresses

Rakesh Gandhi (editor)
Cisco Systems, Inc.
Canada
Greg Mirsky (editor)
Individual
Haoyu Song
Futurewei Technologies
United States of America
Bin Wen
Comcast
United States of America
Voitek Kozak
Comcast
United States of America