Internet-Draft IOAM Using MPLS Network Actions July 2026
Gandhi, et al. Expires 19 January 2027 [Page]
Workgroup:
MPLS Working Group
Internet-Draft:
draft-ietf-mpls-mna-ioam-07
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, is an on-path telemetry method to collect and record the operational state and telemetry information using, for example, Pre-allocated Trace, Proof-of-Transit, Edge-to-Edge, or Incremental Trace Option-Types that can be used to calculate 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 are meant to 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 on-path operational state, and telemetry information using IOAM data fields as well as using direct export.

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 19 January 2027.

Table of Contents

1. Introduction

In situ OAM (IOAM) [RFC9197] is an on-path telemetry method used to collect and record the operational state and telemetry information that can be used to calculate various performance metrics. Several IOAM Option-Types (e.g., Pre-allocated Trace, Proof-of-Transit (POT), Edge-to-Edge (E2E), and Incremental Trace) use user packets to collect the operational state and telemetry information. Such mechanisms transport the collected information to an IOAM decapsulating node (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 also allow for the transport of data needed for these actions. [RFC9994] defines mechanisms for carrying the 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 on-path operational state and telemetry information using IOAM data fields for IOAM Option-Types, IOAM Pre-allocated Trace, POT, E2E, and 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 Incremental Trace IOAM Option-Type is outside the scope of this document.

2. Conventions Used in This Document

2.1. Acronyms

OAM: Operations, Administration, and Maintenance

HBH: Hop-by-Hop

I2E: Ingress-to-Egress

IHS: Ingress-to-Egress (I2E), Hop-by-Hop (HBH) or Select Scope

IOAM: In situ OAM

IOAM-DEX: IOAM Direct Export

IOAM-DEX-ISD-MNA: IOAM Direct Export as MPLS Network Action ISD

ISD: In-Stack Data

PFN: Post-Stack First Nibble

PSD: Post-Stack Data

PSMH: Post-Stack MPLS Header

LSE: Label Stack Entry

MPLS: Multiprotocol Label Switching

MNA: MPLS Network Action

NAI: Network Action Indicator

NAS: Network Action Sub-Stack

NASL: Network Action Sub-Stack Length

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 the telemetry information within a user packet may noticeably decrease 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] is capable of collecting the IOAM data fields defined in [RFC9197]. In this document, the In-Stack and Post-Stack realizations of IOAM-DEX are defined in Section 4.2 and Section 4.1, respectively.

The procedure defined in this document to carry 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 to transport IOAM Option-Types using the MNA solution defined in this document, with Simple Two-Way Active Measurement Protocol (STAMP) test packets for Hop-by-Hop (HBH) and E2E measurements.

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 in the NAS as defined in [I-D.ietf-mpls-mna-ps-hdr] and 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 |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Opcode     |  16-bit Data (Format C)       |S|4b Data|U| NAL |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                Label                  | TC  |1|  TTL          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~ Post-Stack MPLS Header for IOAM and IOAM-DEX as 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].

The IHS scope field defined in [RFC9994] is used to indicate that I2E, HBH, or Select processing is required for the Network Action and Ancillary Data.

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

U: The U flag for Unknown Action Handling is specified in [RFC9994].

S: The Bottom of Stack bit [RFC3032].

IHS (2-bit): The IHS field is set as specified in [RFC9994].

P: The P flag is set as specified in [I-D.ietf-mpls-mna-ps-hdr].

NASL (4-bit): The Network Action Sub-Stack Length (NASL) is set as specified in [RFC9994].

Opcode (7-bit): Opcode TBA1 for Network Action for IOAM and IOAM-DEX in PSD, for carrying an IOAM Option-Type and the associated data fields defined in [RFC9197] and the IOAM-DEX Option-Type and the associated data fields defined in [RFC9326], both in the PSMH. This network action is optional and can be carried in a Format B or Format C Label Stack Entry (LSE).

The Data (13-bit, next to the Opcode field) in the LSE contains the PSMH offset for this In-Stack Network Action in 4-octet units after the BoS LSE to the start of the corresponding Post-Stack Network Action Opcode. Due to the Post-Stack MPLS Base Header, the minimum value for the offset is 1 (i.e., 4 octets).

NAL (3-bit): The Length of Network Action (NAL) [RFC9994] is set to 0 for the In-Stack Network Action for the IOAM and IOAM-DEX Option-Type in Post-Stack ancillary data.

A packet may carry more than one In-Stack Network Action in an MNA Sub-Stack for IOAM and IOAM-DEX in the PSMH (for example, for different IOAM Option-Types as identified in Post-Stack ancillary data). There may be a different In-Stack Network Action (other than for the IOAM and IOAM-DEX) in the In-Stack MNA Sub-Stack.

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

An example encoding for IOAM and IOAM-DEX carried in a PSMH 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 that 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 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 number of 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 4.4 of [RFC9197] and the IOAM-DEX Option-Type in Section 3 of [RFC9326]).

An IOAM Option-Type is added in the PSMH containing the following fields:

MNA-PS-OP (7-bit):
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):
The unsigned integer. 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 4.4 of [RFC9197] and Section 3 of [RFC9326]).
Block-Number (8-bit):
The block number for the alternate marking method can be used to aggregate the IOAM data collected in the data plane, e.g., to compute measurement metrics for each block of a data flow. It is also used to correlate the collected IOAM data from different nodes along the packet path. The block number is incremented sequentially at every measurement interval provisioned on the encapsulating node.
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 uses all the elements of the IOAM-DEX Option-Type format defined in [RFC9326] to support IOAM-DEX in an MPLS network using MNA ISD [RFC9994].

To support the direct export of the operational state and telemetry information, the IOAM-DEX-ISD-MNA blob (binary large object) 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-ISD-MNA can operate in Hop-by-Hop, Ingress-to-Egress, 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-ISD-MNA as 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) as defined in [RFC9994].
  • S: The Bottom of Stack bit [RFC3032].
  • P: The P flag is set as specified in [I-D.ietf-mpls-mna-ps-hdr].
  • The IHS, U, and NAL fields are set as specified in [RFC9994].
  • NASL (4-bit): The number of LSEs that compose the IOAM-DEX-ISD-MNA blob.
  • Opcode (7-bit): Set to TBA2 for MNA-IOAM-DEX.
  • Data: Data field is not used and set to 0.
  • IOAM-DEX-ISD-MNA: 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-ISD-MNA 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-ISD-MNA 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 [RFC9197].
  • Reserved (6-bit): The Reserved field MUST be set to 0 on transmit and ignored on receipt.
  • S: The Bottom of Stack bit [RFC3032].
  • Flags (8-bit): The flags field comprises of eight one-bit subfields. The subfields in the Flags field are allocated by IANA in the IOAM-DEX Flags registry, as defined in Section 4.2 of [RFC9326].
  • IOAM-Trace-Type-MNA (22-bit): The interpretation of bit positions in the IOAM-Trace-Type-MNA is as specified in [RFC9197], from bit 0 through bit 21. 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 marked as "variable-length Opaque State Snapshot" as defined in [RFC9197] and assigned code points 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 marked as "reserved" as defined in [RFC9197] and assigned code points found in IANA's IOAM Trace-Type registry [IANA-IOAM-Trace-Type]. Similarly to [RFC9197], 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 its 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 of six one-bit subfields. The allocation of the subfields in the Ext-Flags field is according to Section 4.3 of [RFC9326]. The allocated flags indicate the presence of the optional Flow ID MNA and/or Sequence Number MNA fields in the IOAM-DEX-ISD-MNA header. 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]. However, currently only two flags have been assigned by IANA as defined in Section 4.3 of [RFC9326], and six flags have not been assigned by IANA. Similarly, in the Ext-Flags of the IOAM-DEX-ISD-MNA header, two flags have been mapped to those IANA assigned flags in the IOAM-DEX Option-Type, and four 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 and carries 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 and carries 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|N|U|U|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-ISD-MNA header.
  • N: One-bit flag. When the N flag is set to 1, it indicates the presence of the Sequence Number field in the IOAM-DEX-ISD-MNA header.
  • 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 I2E IOAM data fields carry IOAM Option-Types that require processing on the encapsulating and decapsulating nodes only.

The IOAM Option-Type carried can be the IOAM E2E Option-Type (value 3) defined in [RFC9197] as well as the IOAM-DEX Option-Type (value 4) defined in [RFC9326]. The I2E IOAM data fields 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 I2E IOAM and IOAM-DEX Network Action procedure is summarized as follows:

  • The encapsulating node inserts an MNA Sub-Stack with the MNA Label with the IHS scope set to "I2E, value 0x0", one or more In-Stack Network Actions, and one or more IOAM data fields in the MPLS packet.
  • The intermediate nodes do not process the I2E IOAM data fields.
  • The decapsulating node MAY punt the IOAM data fields from the packet with the receive timestamp to the slow path for processing. The receive timestamp is required by the various I2E IOAM 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 [RFC9197] and [RFC9326]. An example of IOAM processing is to export the IOAM data fields for streaming telemetry.
  • The decapsulating node MUST remove the Network Actions and IOAM data fields from the received packet. The decapsulated packet is forwarded downstream or terminated locally similar to the regular data packets.

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

The HBH IOAM data fields carry IOAM Option-Types that require processing at the intermediate and/or encapsulating and decapsulating nodes.

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

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

The Hop-by-Hop IOAM and IOAM-DEX Network Action procedure is summarized as follows:

  • The encapsulating node inserts an MNA Sub-Stack containing the MNA Label, with the IHS scope set to "HBH, value 0x1", one or more In-Stack Network Actions for IOAM, and one or more IOAM data fields in the MPLS packet.
  • The intermediate node that is enabled for the HBH IOAM function processes the data packet including the IOAM data fields as defined in [RFC9197] and [RFC9326] when the node recognizes the HBH scope in the MNA Sub-Stack.
  • The intermediate node MAY punt the IOAM data fields from the packet with the receive timestamp to the slow path for processing when the node recognizes the HBH scope. The receive timestamp is required by the various HBH IOAM use cases, including streaming telemetry. Note that the packet is not necessarily punted to the control-plane.
  • The intermediate node forwards the data packet downstream.
  • The processing on the decapsulating node is the same as in the I2E case.

Both HBH and I2E Scope IOAM may be carried in the Post-Stack MNA in an MPLS packet. In this case, the PSMH with HBH IOAM data fields MUST be added after the BoS and before the PSMH with I2E IOAM data fields. This way, the RLD required to process them on the intermediate nodes is minimized.

5.3. Node Capability

The decapsulating node that needs to remove the IOAM and IOAM-DEX data fields and perform the IOAM and IOAM-DEX functions may not be capable of supporting them. The encapsulating node needs to know if the decapsulating 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 MNA Sub-Stack 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 make sure that the IOAM and IOAM-DEX data fields in the MNA are added within the Readable Label Depth (RLD) of the downstream MNA-capable nodes in order for them to be able to process the IOAM and IOAM-DEX.

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.

7. Security Considerations

Security considerations discussed in [RFC9197], [RFC9326], [RFC9994], [I-D.ietf-mpls-mna-ps-hdr] and [RFC9789] 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. Still, 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 (creation requested in [RFC9994] and update requested in [I-D.ietf-mpls-mna-ps-hdr]) as specified in Table 1.

Table 1: 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 In-Stack and Post-Stack This document
TBA2 Network Action for IOAM-DEX in ISD In-Stack Only This document

9. Appendix A: Examples

9.1. In-Stack and Post-Stack Network Action Processing Order

The In-Stack Network Action with Post-Stack Data can be added to interleave Post-Stack network actions with In-Stack network actions. The following example shows how to process the Post-Stack NA before some of the In-Stack NAs.

  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=8    |      Ancillary Data     |1|IHS|0| NASL=3|U|NAL=0|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Opcode=1    |      Flag-Based NAIs          |0| NAIs  |U|NAL=0|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Opcode=TBA1 |      Post-Stack Offset=1      |0|PS-NAI |U|NAL=0|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Opcode=7    |      Ancillary Data           |1|  AD   |U|NAL=0|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | PFN   |Reserve|    PSMH-Len=1 | Type = MNA Post-Stack Header  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | PS-OP=TBA1  |R|R|  PS-NAL=0   |       Post-Stack Data         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Post-Stack and In-Stack NA Processing Order

In this example, opcode 8 is processed first, followed by opcode 1 for Flag-Based NAIs, then opcode TBA1 (which has the corresponding Network Action opcode TBA1 in Post-Stack at an offset of 1 word, i.e., 4 octets from the BoS), and finally opcode 7.

10. References

10.1. Normative References

[I-D.ietf-mpls-mna-ps-hdr]
Rajamanickam, J., Gandhi, R., Zigler, R., Dong, J., and J. Bhattacharya, "Post-Stack MPLS Network Action (MNA) Header Specification", Work in Progress, Internet-Draft, draft-ietf-mpls-mna-ps-hdr-10, , <https://datatracker.ietf.org/doc/html/draft-ietf-mpls-mna-ps-hdr-10>.
[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>.
[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>.

10.2. Informational References

[I-D.gandhi-ippm-stamp-mpls-hdr]
Gandhi, R., Zhou, T., Li, Z., and F. Ihle, "Simple Two-Way Active Measurement Protocol (STAMP) Extensions for Reflecting STAMP Packet MPLS Extension Headers", Work in Progress, Internet-Draft, draft-gandhi-ippm-stamp-mpls-hdr-07, , <https://datatracker.ietf.org/doc/html/draft-gandhi-ippm-stamp-mpls-hdr-07>.
[IANA-IOAM-Trace-Type]
IANA, "IOAM Trace-Type", <https://www.iana.org/assignments/ioam/ioam.xhtml#trace-type>.
[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>.

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.

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