]> Cisco Systems, Inc.

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Futurewei Technologies

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Comcast

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Comcast

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Routing MPLS Working Group Internet-Draft IOAM MPLS Network Action 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, Edge-to-Edge, 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 Direct Export.

Introduction In situ Operations, Administration, and Maintenance (IOAM) 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) 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 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. defines mechanisms for carrying a Network Action Sub-Stack (NAS) as part of the MPLS label stack, i.e., the In-Stack MNA solution. defines mechanisms for carrying MNA and Ancillary Data (AD) below the MPLS label stack, i.e., as the Post-Stack MNA solution. 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 data fields for 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.

Conventions Used in This Document

Acronyms The terminology defined in , , and is used in this document. Acronyms

Abbreviation	Meaning	Reference
HbH	Hop-by-Hop
I2E	Ingress to Egress
E2E	Edge-to-Edge
IHS	I2E, HbH, or Select
IOAM	In situ Operations, Administration, and Maintenance
IOAM-DEX	IOAM Direct Export
IOAM-DEX-MNA-ISD	IOAM Direct Export as MPLS Network Action ISD	This document
ISD	In-Stack Data
LSE	Label Stack Entry
MNA	MPLS Network Action
MPLS	Multiprotocol Label Switching
NAI	Network Action Indicator
NAL	Network Action Length
NAS	Network Action Sub-Stack
NASL	Network Action Sub-Stack Length
OAM	Operations, Administration, and Maintenance
POT	Proof-of-Transit
PFN	Post-Stack First Nibble
PSD	Post-Stack Data
PSMH	Post-Stack MPLS Header
S	Bottom of Stack bit
TC	Traffic Class
TTL	Time to Live
U bit	Unknown Action Handling bit

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 when, and only when, they appear in all capitals, as shown here.

Applicability of IOAM and IOAM-DEX in an MPLS Network Pre-allocated Trace, POT, and E2E IOAM Option-Types use user packets to collect and transport the operational state and telemetry information. This document defines the Post-Stack MNA solution supporting Pre-allocated Trace, POT, and E2E IOAM Option-Types (). 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 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 allows to collect the IOAM data defined in using on-path telemetry information. In this document, the In-Stack and Post-Stack realizations of IOAM-DEX are specified in and , 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. 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. 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.

Realization of IOAM and IOAM-DEX as MPLS Network Actions

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 . An example of a NAS and the corresponding PSMH carrying IOAM and IOAM-DEX Option-Types is shown in .

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 . The U, NAL, and NASL fields are set as specified in . P: The P bit is set as specified in . Opcode (7-bit): The opcode is set as specified in . The Data (13-bit, next to the Opcode field): The data is set as specified in . The IHS scope field defined in 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.

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 .

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 .

PFN (4-bit):

The Post-Stack First Nibble (PFN) (value 0x0) as defined in .

PSMH-Len (8-bit):

The PSMH total length is set as defined in .

Type (16-bit):

Type for MNA Post-Stack Header (value 1) as defined in .

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 . The IOAM data fields MUST follow the definitions corresponding to their IOAM Option-Types (e.g., see Section 4.4 of and the IOAM-DEX Option-Type in Section 3 of ). 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 , and the IOAM-DEX Option-Type defined in .

IOAM-Opt-Type (7-bit):

The field to carry the IOAM Option-Type, as defined in the "IOAM Option-Type Registry" in and .

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 4.4 of and Section 3 of ).

Block-Number (8-bit):

The block number for the alternate marking method is 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.

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 .

Example of Multiple Post-Stack Network Actions with IOAM and IOAM-DEX with the Same Scope

Realization of IOAM-DEX as In-Stack MNA This document uses all the elements of the IOAM-DEX Option-Type format defined in to support IOAM-DEX in an MPLS network using MNA In-Stack Data (ISD) . To support the direct export of the operational state and telemetry information, the IOAM-DEX-MNA-ISD 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 . Using the IHS field, the IOAM-DEX-MNA-ISD can operate in Hop-by-Hop, Ingress-to-Egress, or Select modes to collect the operational state and telemetry information using an MNA Opcode ().

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 .
• The IHS, U, and NAL fields are set as specified in .
• P: The P bit is set as specified in .
• NASL (4-bit): The number of LSEs that compose the IOAM-DEX-MNA-ISD blob.
• Opcode (7-bit): Set to TBA2 for MNA-IOAM-DEX.
• 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.

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 , that maps to the IOAM-DEX Option-Type format . 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 . The format of the IOAM-DEX-MNA-ISD blob in an NAS is shown in .

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 .
• 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 .
• IOAM-Trace-Type-MNA (22-bit): The interpretation of bit positions in the IOAM-Trace-Type-MNA is as specified in , from bit 0 through bit 21. Note that bits as specified in are right-shifted one bit, so for example, bit 0 in (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 .
• O: This is a one-bit flag identical to the interpretation of bit 22 marked as "variable-length Opaque State Snapshot" as defined in and assigned code points found in IANA's IOAM Trace-Type registry .
• R: This is a one-bit flag identical to the interpretation of bit 23 marked as "reserved" as defined in and assigned code points found in IANA's IOAM Trace-Type registry . Similarly to , 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 , and in the interpretation of those bits as defined in and assigned code points found in IANA's IOAM Trace-Type registry .
• 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 . The allocated flags indicate the presence of the optional Flow ID MNA and/or Sequence Number MNA fields in the IOAM-DEX-MNA-ISD 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 . However, currently only two flags have been assigned by IANA as defined in Section 4.3 of , and six flags remain unassigned in that registry. Similarly, in the 6-bit Ext-Flags field of the IOAM-DEX-MNA-ISD header, two flags have been mapped to those IANA assigned flags in the IOAM-DEX Option-Type, and four flags remain unmapped. displays the detailed format of the Ext-Flags field.
• According to Section 3.2 in , 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 . The most significant bit MUST be set to 1. The bit 23 MUST be set according to the definition of the S bit in .
• 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 . The most significant bit MUST be set to 1. The bit 23 MUST be set according to the definition of the S bit in . 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.

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.
• 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-MNA-ISD header.
• U: Unassigned one-bit flag. It MUST be set to zero on transmission and the value MUST be ignored upon receipt.

Considerations for IOAM and IOAM-DEX in MPLS Networks

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 or the IOAM-DEX Option-Type (value 4) defined in . 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 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 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 and . 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 similar to the regular data packets or terminated locally.

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 Pre-allocated Trace (value 0), POT (value 2), or E2E (value 3) defined in , or IOAM-DEX (value 4) defined in . 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 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 HbH IOAM function processes the data packet including the IOAM data fields as defined in and when the node recognizes the HbH scope in the NAS.
• 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 and IOAM-DEX 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 minimizes the Readable Label Depth (RLD) required for intermediate node processing.

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.

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.

Readable Label Depth Consideration The encapsulating node needs to ensure that the IOAM and IOAM-DEX data fields in an MNA are added within the RLD of the downstream MNA-capable nodes so that they can process the IOAM and IOAM-DEX data fields.

Operational Considerations Operational considerations discussed in and , management considerations discussed in , and management and deployment considerations discussed in apply to this document. The performance considerations discussed in Section 5 of are also applicable here. Additional operational considerations are described in Section 5 for deploying IOAM and IOAM-DEX in MPLS networks.

Security Considerations Security considerations discussed in , , , , and 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.

IANA Considerations

MPLS Network Action Opcodes IANA is requested to assign code points from its Network Action Opcodes registry (created in and updated in ) as specified in . 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

Appendix A: Examples

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.

Post-Stack and In-Stack Nework Action Processing Order

In this example, shown in Figure 7, opcode 8 is processed first, followed by opcode 1 for Flag-Based NAIs, then opcode TBA3 (PSMH Start Offset defined in ), and the corresponding PSMH (with opcode TBA1), and finally opcode 7.

References Normative References Informative References IANA

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: