MPLS Network Action (MNA) Sub-Stack Specification including In-Stack Network Actions and Data
draft-ietf-mpls-mna-hdr-20
| Document | Type | Active Internet-Draft (mpls WG) | |
|---|---|---|---|
| Authors | Jaganbabu Rajamanickam , Rakesh Gandhi , Royi Zigler , Haoyu Song , Kireeti Kompella | ||
| Last updated | 2026-02-06 | ||
| Replaces | draft-jags-mpls-mna-hdr | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Reviews |
TSVART Telechat review
(of
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by Brian Trammell
Ready w/issues
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Associated WG milestone |
|
||
| Document shepherd | Tarek Saad | ||
| Shepherd write-up | Show Last changed 2025-10-14 | ||
| IESG | IESG state | IESG Evaluation::AD Followup | |
| Action Holder | |||
| Consensus boilerplate | Yes | ||
| Telechat date |
(None)
Has a DISCUSS. Has enough positions to pass once DISCUSS positions are resolved. |
||
| Responsible AD | Jim Guichard | ||
| Send notices to | tsaad@cisco.com | ||
| IANA | IANA review state | Version Changed - Review Needed |
draft-ietf-mpls-mna-hdr-20
MPLS Working Group J. Rajamanickam, Ed.
Internet-Draft R. Gandhi, Ed.
Intended status: Standards Track Cisco Systems, Inc.
Expires: 10 August 2026 R. Zigler
Broadcom
H. Song
Futurewei Technologies
K. Kompella
Juniper Networks
6 February 2026
MPLS Network Action (MNA) Sub-Stack Specification including In-Stack
Network Actions and Data
draft-ietf-mpls-mna-hdr-20
Abstract
This document specifies the MPLS Network Actions (MNA) sub-stack for
carrying Network Actions and Ancillary Data in the MPLS label stack.
MNA can be used to influence packet forwarding decisions, carry
additional Operations, Administration, and Maintenance information in
the MPLS packet or perform user-defined operations.
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 10 August 2026.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Label Stack Entry Formats . . . . . . . . . . . . . . . . . . 7
4.1. LSE Format A: The MNA Sub-Stack Indicator . . . . . . . . 7
4.2. LSE Format B: The initial opcode . . . . . . . . . . . . 7
4.3. LSE Format C: Subsequent opcodes . . . . . . . . . . . . 8
4.4. LSE Format D: Additional Data . . . . . . . . . . . . . . 9
5. The MNA Sub-Stack . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2. Ancillary Data . . . . . . . . . . . . . . . . . . . . . 10
5.3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.4. Unknown Network Action Handling . . . . . . . . . . . . . 12
5.5. Ordering . . . . . . . . . . . . . . . . . . . . . . . . 13
6. Special Opcodes . . . . . . . . . . . . . . . . . . . . . . . 13
6.1. bSPL Protection . . . . . . . . . . . . . . . . . . . . . 13
6.2. Flag-Based NAIs without AD . . . . . . . . . . . . . . . 13
6.3. No-Operation Opcode . . . . . . . . . . . . . . . . . . . 14
6.4. Extension Opcode . . . . . . . . . . . . . . . . . . . . 14
7. NAS placement in the Label Stack . . . . . . . . . . . . . . 14
7.1. Actions when Pushing Labels . . . . . . . . . . . . . . . 15
8. Node Capability Signaling . . . . . . . . . . . . . . . . . . 16
9. Processing the Network Action Sub-Stack . . . . . . . . . . . 16
9.1. Encapsulating Node Responsibilities . . . . . . . . . . . 17
9.2. Transit Node Responsibilities . . . . . . . . . . . . . . 17
9.3. Penultimate Node Responsibilities . . . . . . . . . . . . 17
9.4. Egress Node Responsibilities . . . . . . . . . . . . . . 17
10. Network Action Indicator Opcode Definition . . . . . . . . . 17
11. Implementation Status . . . . . . . . . . . . . . . . . . . . 18
11.1. University of Tuebingen Implementation . . . . . . . . . 19
12. Security Considerations . . . . . . . . . . . . . . . . . . . 19
13. Operational Considerations . . . . . . . . . . . . . . . . . 20
13.1. Manageability Considerations . . . . . . . . . . . . . . 20
13.2. Performance and Scale Considerations . . . . . . . . . . 20
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13.3. Backward Compatibility . . . . . . . . . . . . . . . . . 21
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
14.1. MNA bSPL Label . . . . . . . . . . . . . . . . . . . . . 22
14.2. MPLS Network Actions Parameters . . . . . . . . . . . . 22
14.3. Network Action Flags Without Ancillary Data . . . . . . 22
14.4. Network Action Opcodes . . . . . . . . . . . . . . . . . 23
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
15.1. Normative References . . . . . . . . . . . . . . . . . . 24
15.2. Informative References . . . . . . . . . . . . . . . . . 25
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 26
A.1. Network Action Encoding Examples . . . . . . . . . . . . 26
A.1.1. Network Action Flags without AD . . . . . . . . . . . 26
A.1.2. Network Action Opcode with AD . . . . . . . . . . . . 27
A.1.3. Network Action Opcode with more AD with Format-B . . 28
A.1.4. Network Action Opcode with more AD with Format C . . 29
A.2. Network Action Processing Order . . . . . . . . . . . . . 30
A.2.1. Network Action Processing Order . . . . . . . . . . . 30
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 31
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32
1. Introduction
[RFC3032] defines the encoding of the MPLS label stack, the basic
structure used to define a forwarding path. There are applications
that require MPLS packets to perform special network actions and
carry optional Ancillary Data (AD) that can affect the packet
forwarding decision or trigger Operations, Administration, and
Maintenance (OAM) logging, for example as described in [RFC9791].
Ancillary Data can be used to carry additional information, for
network slice purpose, as an example [RFC9791].
The requirements for In-stack network action and In-stack data (ISD)
are described in [RFC9613].
This document defines the syntax and semantics of network actions and
ancillary data encoded in an MPLS label stack. In-stack actions and
ancillary data are contained in a Network Action Sub-Stack (NAS),
which is recognized by a new base Special Purpose Label (bSPL). This
document follows the framework specified in [RFC9789].
2. Conventions Used in This Document
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2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, [RFC2119]
[RFC8174] when, and only when, they appear in all capitals, as shown
here.
2.2. Abbreviations
The abbrevations defined in [RFC9789] and [RFC9613] are used in this
document.
+==============+=============================+===============+
| Abbreviation | Meaning | Reference |
+==============+=============================+===============+
| AD | Ancillary Data | [RFC9613] |
+--------------+-----------------------------+---------------+
| bSPL | Base Special Purpose Label | [RFC9017] |
+--------------+-----------------------------+---------------+
| BOS | Bottom Of Stack | [RFC9789] |
+--------------+-----------------------------+---------------+
| ECMP | Equal Cost Multi-Path | [RFC6790] |
+--------------+-----------------------------+---------------+
| HBH | Hop-By-Hop Scope | [RFC9789] |
+--------------+-----------------------------+---------------+
| I2E | Ingress-To-Egress Scope | [RFC9789] |
+--------------+-----------------------------+---------------+
| IHS | I2E, HBH, or Select Scope | [RFC9789], |
| | | This document |
+--------------+-----------------------------+---------------+
| ISD | In-stack Data | [RFC9613] |
+--------------+-----------------------------+---------------+
| LSE | Label Stack Entry | [RFC9789] |
+--------------+-----------------------------+---------------+
| LSP | Label Switched Path | [RFC3031] |
+--------------+-----------------------------+---------------+
| MNA | MPLS Network Actions | [RFC9789] |
+--------------+-----------------------------+---------------+
| NAI | Network Action Indicator | [RFC9613] |
+--------------+-----------------------------+---------------+
| NAL | Network Action Length | This document |
+--------------+-----------------------------+---------------+
| NAS | Network Action Sub-Stack | [RFC9789] |
+--------------+-----------------------------+---------------+
| NASI | Network Action Sub-Stack | This document |
| | Indicator | |
+--------------+-----------------------------+---------------+
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| NASL | Network Action Sub-Stack | This document |
| | Length | |
+--------------+-----------------------------+---------------+
| OAM | Operations, Administration, | [RFC6291] |
| | and Maintenance | |
+--------------+-----------------------------+---------------+
| RLD | Readable Label Depth | [RFC9789] |
+--------------+-----------------------------+---------------+
| TC | Traffic Class | [RFC5462] |
+--------------+-----------------------------+---------------+
| TTL | Time To Live | [RFC3032] |
+--------------+-----------------------------+---------------+
Table 1: Abbreviations
2.3. Terminology
The following terms are used in this document.
MPLS egress node:
An MPLS edge node in its role in handling traffic as it leaves an
MPLS domain [RFC3031].
MPLS ingress node:
An MPLS edge node in its role in handling traffic as it enters an
MPLS domain [RFC3031].
MPLS domain:
A contiguous set of nodes which operate MPLS routing and
forwarding and which are also in one Routing or Administrative
Domain [RFC3031].
Encapsulating Node:
An encapsulating node is a node that adds an NAS to the label
stack.
3. Overview
The MPLS Network Action Sub-Stack is a set of Label Stack Entries
(LSEs) that appear as part of an MPLS label stack and serve to encode
information about the network actions that should be invoked for the
packet. Multiple NASes may appear in a label stack and be placed as
described in Section 5.
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This document specifies how network actions and their optional
ancillary data are encoded as part of a NAS as a stack of LSEs.
Mechanisms that allow sharing of ancillary data (AD) between multiple
network actions encoded in the same NAS can be described in other
documents and do not rely on any explicit provision in the encodings
described in this document.
This document defines new LSE formats beyond [RFC3032] that define
behaviors or are processed in different ways to MPLS labels as
defined in [RFC3031]. Three new LSE formats are defined to carry 7
bits of network action opcodes and varying amounts of opcode-specific
ancillary data. Specifically, Format-B LSE carries up to 13 bits of
ancillary data in an LSE and Format-C LSE carries up to 20 bits of
ancillary data in an LSE. Format-D LSE is used when additional
ancillary data is needed by the opcodes in Format-B or Format-C LSEs.
As shown in an example in the Figure 1, the first LSE in an MNA Sub-
Stack uses Format-A. The second LSE uses Format-B and is followed by
a Format-D LSE to carry additional data. Next, there may be a
Format-C LSE for an additional network action followed by another
Format-D LSE for additional data. You can add more Format-C and
Format-D LSEs as needed for additional network actions and data.
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=bSPL | TC |S| TTL |A
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--
| Opcode | 13-bit Data |R|IHS|S| NASL |U| NAL |B
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--
|1| 22-bit Data |S| 8-bit Data |D*
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--
| Opcode | 16-bit Data |S|4b Data|U| NAL |C
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--
|1| 22-bit Data |S| 8-bit Data |D*
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--
| Opcode | 16-bit Data |S|4b Data|U| NAL |C
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--
Legend: * Format-D LSE presence indicated by NAL greater than one
Figure 1: An MNA Sub-Stack Encoding Example
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4. Label Stack Entry Formats
The NAS uses a variety of different formats of LSEs for different
purposes. This section describes the syntax of the various formats
while the overall structure of the NAS and the semantics of the
various LSEs are described in the sections below.
4.1. LSE Format A: The MNA Sub-Stack Indicator
LSE Format A is an LSE as described in [RFC3032] and [RFC5462]. The
label value is an IANA-assigned value (TBA) for the MNA bSPL label
from the "Base Special-Purpose MPLS Label Values" registry to
indicate the presence of MNA in the packet and the beginning of an
MNA Sub-Stack in the label stack.
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=bSPL | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: LSE Format A: The MNA Sub-Stack Indicator
* S (1 bit): The Bottom of Stack [RFC3032]. MUST be set to 0 on
transmitted packets. If a packet is received with an LSE
containing the bSPL (value TBA) and with S bit set to 1, then the
packet MUST be dropped.
4.2. LSE Format B: The initial opcode
LSE Format B is used to encode the first opcode in the NAS, plus a
number of other fields about the NAS. This LSE can carry up to 13
bits of ancillary data.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode | 13-bit Data |R|IHS|S| NASL |U| NAL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: LSE Format B: The initial opcode
* Opcode (7 bits): The operation code for this LSE. See
Section 5.1.
* Data (13 bits): Opcode-specific ancillary data.
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* R (1 bit): Reserved. This bit MUST be set to zero on transmission
and ignored upon receipt.
* IHS (2 bits): The scope of all the network actions in this NAS.
See Section 5.3.
* S (1 bit): The Bottom of Stack [RFC3032]. If NASL value is non-
zero, then S bit MUST be 0. If a packet is received with S bit
set to 1 and a non-zero NASL value, then the packet MUST be
dropped. The encapsulating node MUST ensure that the S bit is set
to 1 only in the Last LSE in the MPLS header.
* NASL (4 bits): The Network Action Sub-Stack Length (NASL). The
number of Format C and Format D LSEs in the NAS, i.e., not
including the leading Format A LSE and the Format B LSE.
* U (1 bit): Unknown Network Action Handling. See Section 5.4.
* NAL (3 bits): Network Action Length. The number of LSEs of
additional data, encoded in Format D LSEs (Section 4.4) following
this Format B LSE. The NAL value MUST be less than or equal to
the NASL value in the Format B LSE, if not the packet MUST be
dropped. A Format C LSE would be following when the NAL value is
less than the NASL value.
4.3. LSE Format C: Subsequent opcodes
LSE Format C is used to encode the subsequent opcodes in the 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode | 16-bit Data |S|4b Data|U| NAL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: LSE Format C: Subsequent opcodes
* Opcode (7 bits): The operation code for this LSE. See
Section 5.1.
* Data (16 bits + 4 bits): Opcode-specific ancillary data.
* S (1 bit): The Bottom of Stack [RFC3032]. If NAL value is non-
zero and if S bit is set to 1, then the packet MUST be dropped.
If this is not the last LSE in the NAS and if S bit is set to 1
then the packet MUST be dropped. The encapsulating node MUST
ensure that the S bit is set to 1 only in the Last LSE.
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* U (1 bit): Unknown Network Action Handling. See Section 5.4.
* NAL (3 bits): Network Action Length. The number of LSEs of
additional data, encoded in Format D LSEs (Section 4.4) following
this Format C LSE. The NAL value MUST be less than or equal to
the NASL value in the Format B LSE, if not the packet MUST be
dropped.
A Format A and a Format B LSE MUST be present when a Format C LSE is
carried in the NAS.
4.4. LSE Format D: Additional Data
LSE Format D is used to encode additional data that did not fit in
the LSE with the preceding opcode.
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| 22-bit Data |S| 8-bit Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: LSE Format D: Additional Data
* 1 (1 bit): The most significant bit MUST be set. This prevents
legacy implementations from misinterpreting this LSE as containing
a special purpose label if the data begins with zeros.
* S (1 bit): The Bottom of Stack [RFC3032]. If this is not the last
LSE for the Network Action based on the NAL value and if S bit is
set to 1 then the packet MUST be dropped. If this is not the last
LSE in the NAS and if S bit is set to 1 then the packet MUST be
dropped. The encapsulating node MUST ensure that the S bit is set
to 1 only in the Last LSE.
* Data (22 bits + 8 bits): Opcode-specific ancillary data.
A Format A and a Format B LSE MUST be present when a Format D LSE is
carried in the NAS.
5. The MNA Sub-Stack
The MNA Sub-Stack MUST begin with a Format A LSE (Section 4.1). The
label value of the LSE contains the MNA bSPL (value TBA) to indicate
the presence of the MNA Sub-Stack.
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The TC and TTL values of the Format A LSE retain their semantics as
defined in [RFC3032] and [RFC5462]. The TTL and TC values in the
Format A LSE are copied from the forwarding label at the top of the
label stack. The penultimate node on the path copies the TTL and TC
values from the preceding LSE to the next LSE on the label stack,
overwriting the TTL and TC values of the next LSE, as specified in
Section 3.5 of [RFC3443] and Section 2.6.3 of [RFC3270] in the
Uniform Mode LSPs. If the node performing this copy is not aware of
MNA, this could overwrite the values in the Format-A LSE of the NAS.
The second LSE in a NAS MUST be a Format B LSE (Section 4.2). This
LSE contains an initial opcode plus additional fields that describe
the NAS.
The Format B LSE (Section 4.2) could optionally carry additional data
in Format D (Section 4.4) LSEs, up to the length encoded in the LSE's
NAL value.
A NAS MAY contain more Format C (Section 4.3) and Format D
(Section 4.4) LSEs, up to the length encoded in the NASL value. All
Format D LSEs MUST follow a Format C or B LSE and be included in that
LSE's NAL value.
5.1. Opcodes
The opcode is a 7-bit field that indicates the semantics of its LSE.
Several opcodes are assigned special semantics (Section 6), others
act as Network Action Indicators and are assigned through IANA
(Section 10 and Section 14.4).
5.2. Ancillary Data
The data field carries opcode-specific data that is ancillary data
for a network action. In the case of opcode 1, the data field
carries Flag-Based Network Action Indicators without ancillary data.
The label value (most significant 20 bits) in one or more consecutive
LSEs is commonly used for load balancing data flows in an ECMP
environment. Modifying the first 20 bits in an LSE might alter a
packet's path and result in out-of-order delivery of packets
belonging to a given flow. To maintain the stability of deployed
services in ECMP environments that rely on label value information
for load-balancing, care must be taken when encoding network action
data in the given LSE. If the network action data may differ among
packets in the same flow or change during forwarding across the MPLS
network, it MUST NOT be placed in the most significant 20 bits of a
Format B LSE (Section 4.2), a Format C LSE (Section 4.3), or a Format
D LSE (Section 4.4). Thus, the available bits for data that can
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change by a transit node or differ among packets of the same flow in
Format A and Format B LSEs are 0, Format C LSE is 7 (bits 20-22 and
25-28) and Format D LSE is 11 (bits 20-22 and 24-31).
Similarly, to preserve service stability, such data also MUST NOT be
carried in the most significant 23 bits of these LSEs when the legacy
implementation also uses the TC value, in addition to the label
value, in all LSEs when computing ECMP decisions.
The available mitigations for these problems are to use additional
Format D LSEs to carry the data, or to place the data in Post-Stack
Data as described in [RFC9789].
In network deployments where it is known that a load-balancing of
data flows is not used, or, otherwise, if only the explicitly
signaled entropy value is used, and it is certain that the load-
balancing path selection will not be based on the label value of the
LSEs, then the data in the label value of the LSEs in ISD MAY be
mutable within the data flow without causing the out-of-order
delivery of packets.
5.3. Scope
The IHS field in the Format B LSE indicates the scope of all the NAIs
encoded in the NAS. Scope defines which nodes along the MPLS path
should perform the network actions found within the NAS. The
specific values of the IHS field are as follows:
+======+=========================+
| Bits | Scope |
+======+=========================+
| 00 | I2E |
+------+-------------------------+
| 01 | HBH |
+------+-------------------------+
| 10 | Select |
+------+-------------------------+
| 11 | Reserved for future use |
+------+-------------------------+
Table 2: IHS Scope Values
Ingress To Egress (I2E) - The Network Actions in this NAS MUST NOT
be processed by any node except the egress node.
Hop-By-Hop (HBH) - All nodes along the path MUST process the NAS.
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Select - Only specific nodes along the path that brings NAS to top
of the stack will perform the action.
A given NAS can only carry NAIs with the same scope (I2E/HBH/Select).
To support multiple scopes for a single packet, multiple NASes MAY be
included in a single label stack.
The egress node is included in the HBH scope. This implies that the
penultimate node MUST NOT remove a HBH NAS. The egress node may
receive a NAS at the top of the label stack as discussed in
Section 9.
An I2E scope NAS, if present, MUST be encoded after any HBH or
Select-scope NASes. This makes it easier for the transit nodes to
process a NAS with HBH or Select scope.
If a packet is received with the IHS scope set to "Reserved for
future use", the packet is processed based on the U bit in the Format
B LSE in the NAS.
5.4. Unknown Network Action Handling
The Unknown Network Action Handling (U) field in a Format B LSE
(Section 4.2) and Format C LSE (Section 4.3) is a 1-bit value that
defines the action to be taken by a node that does not understand an
action within the NAS. The different types of Unknown Network Action
Handling actions are defined below.
+=====+=====================+
| Bit | Action |
+=====+=====================+
| 0 | Skip to the next NA |
+-----+---------------------+
| 1 | Drop the packet |
+-----+---------------------+
Table 3: Unknown Network
Action Handling
When a packet with an unknown Network Action is dropped, the node
should maintain a local counter for this event, and may send a rate-
limited notification to the operator.
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5.5. Ordering
The network actions encoded in the NAS MUST be processed in the order
that they appear in the NAS, from the top of the NAS to the bottom.
NAIs encoded as flags (see Section 6.2) MUST be processed from the
most significant bit to the least significant bit. If a label stack
contains multiple NASes, they MUST be processed in the order that
they appear in the label stack, subject to the restrictions in
Section 7.
6. Special Opcodes
Below are the special opcodes defined to build a basic In-stack MNA
solution and has been assigned through IANA registry (Section 14.4).
In the future, additional special opcodes can be defined and their
code-points assigned from the "Network Action Opcodes" IANA registry
(Section 14.4).
6.1. bSPL Protection
Opcode: 0
Purpose: Legacy implementations may scan the label stack looking for
bSPL values. As long as the opcode field is non-zero, an LSE cannot
be misinterpreted as containing a bSPL. Opcode 0 is therefore
reserved and not to be used.
6.2. Flag-Based NAIs without AD
Opcode: 1
Purpose: This opcode is used for Network actions that do not require
Ancillary Data. A single flag can be used to indicate each of these
network actions.
LSE Formats: B, C, D
Data: The data field carries Network Action Indicators, which should
be evaluated from the most significant bit to the least significant
bit. If this opcode is used with LSE Format B only, then up to 13
flags may be carried. If this opcode is used with LSE Format C only,
then up to 20 flags may be carried. Format D LSEs can be used with
format C LSEs to encode more than 20 flags. Flags are assigned from
the "Network Action Flags Without Ancillary Data" registry
(Section 14.3). If flags need to be evaluated in a different order,
multiple LSEs using this opcode may be used to specify the requested
order. The Flag-Based Network Action Indicators MUST follow the
procedure for data specified in Section 5.2.
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Scope: This opcode can be used with any scope.
6.3. No-Operation Opcode
Opcode: 2
Purpose: This opcode is used to indicate that this opcode does not
perform any Network Action and MUST be skipped.
LSE Format: B
Scope: Any scope value may be set and MUST be ignored.
6.4. Extension Opcode
Opcode: 127
Purpose: This opcode is used to extend the current opcode range
beyond 127 in the future. If this opcode is not supported, then the
packet with the opcode 127 MUST be dropped regardless of the setting
of the U bit. Use of this opcode is outside the scope of this
document.
7. NAS placement in the Label Stack
The node adding a NAS to the label stack places a copy of the NAS
where the relevant nodes can read it. Each downstream node along the
path has a Readable Label Depth (RLD). If the NAS is to be processed
by a downstream MNA-capable node, then the entire NAS MUST be placed
so that it is within RLD by the time the packet reaches the
downstream MNA-capable node.
If the label stack is deep, several copies of the NAS may need to be
encoded in the label stack.
For a NAS with HBH scope, every node will process the top copy of the
NAS, but the NAS MUST NOT appear at the top of the stack at any MNA-
incapable node on the path, that is ensured by the encapsulating node
using the node capability, as described in Section 8.
A NAS MUST NOT appear at the top of the stack after popping the
forwarding label on an MNA-incapable node on the path.
The node behaviour, where a NAS with I2E and HBH scopes is also
removed along with popping the forwarding label on a PHP node, is
outside the scope of this document.
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For a NAS with Select scope, it is processed by the node that brings
it to the top of stack (for example, in the case of using MPLS label
pop operation in Segment Routing) and then the NAS is removed from
the stack. The select-scoped NAS needs to be inserted after the
forwarding label and before the next forwarding label. It could be
inserted before or after a HBH NAS. Note that the case of a NAS with
Select scope with MPLS label swap operation (for example, with RSVP
Traffic Engineering LSPs) is for future study.
For I2E scope, only one copy of the NAS needs to be added at the
bottom of the stack.
Transit, non-penultimate nodes that pop a forwarding label and expose
a copy of a NAS MUST remove it.
An MNA-capable node performing Penultimate Hop Popping (PHP) that
pops the forwarding label with only the NAS(es) remaining on the
stack MUST NOT remove the NAS(es). Instead, it forwards the packet
with the NAS(es) at the top of stack to the next node. Note that the
behavior of the PHP node, as defined in [RFC3270] for TC processing,
and as defined in [RFC3443] for TTL processing, is not modified
regardless of whether the PHP node supports MNA.
The node that receives the NAS at the top of the label stack MUST
process and remove it.
7.1. Actions when Pushing Labels
An MNA-capable node may need to push additional labels as well as
push new network actions onto a received packet.
While pushing additional labels on to the label stack of the received
packet, the MNA-capable node MUST verify that the entire top-most NAS
with HBH scope is still within the RLD of the downstream MNA-capable
nodes. If required, the MNA-capable node MAY create a copy of the
top-most NAS with HBH scope and insert it within the RLD of the
downstream MNA-capable nodes on the label stack.
When an MNA-capable node needs to push a new NAS with HBH scope on to
a received packet that already has a NAS with HBH scope, it SHOULD
copy (and merge) the network actions (including their Ancillary Data)
from the received top-most NAS with HBH scope in the new NAS with HBH
scope. The new NAS MUST be placed within the RLD of the downstream
MNA-capable nodes. This behavior can be based on local policy.
The new network actions added MUST NOT conflict with the network
actions in the received NAS with HBH scope. The mechanism to resolve
such conflicts depend on the network actions and can be based on
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local policy. The MNA-capable node that pushes entries MUST
understand any network actions which it is pushing which may result
in a conflict, and MUST resolve any conflicts between new and
received network actions. In the usual case of a conflict of
duplicating a network action, the definition of a network action MUST
give guidance on conflict resolution.
8. Node Capability Signaling
The encapsulating node MUST make sure that the NAS can be processed
by the transit and egress nodes. In addition, the encapsulated
packet MUST NOT exceed the path MTU as described in [RFC3032].
* The node responsible for selecting a path through the MPLS network
needs to know and consider the MNA-capabilities and RLD of the
transit nodes, and the MNA-capabilities of the egress node as
described in Section 2.3 of [RFC9789].
* Information about the capabilities of the nodes may be configured,
collected through management protocols, or distributed by control
protocols (such as advertising by routing protocols).
* The mechanisms by which the capabilities of the nodes are known by
the node responsible for selecting a path through the MPLS network
are out of scope for this document.
* In the case of MPLS Segment Routing (SR-MPLS), as well as the RLD,
the path computation system needs to know the MSD [RFC8664] that
can be imposed at the ingress node of a given SR path. This
ensures that the label stack depth of a computed path does not
exceed the maximum number of labels (i.e., MSD) the node is
capable of imposing and the maximum number of labels that can be
read by the MNA-processing nodes in the path. The MSD MUST
include the MNA Sub-Stacks that will be added.
* The encapsulating node MAY learn about RLD of the nodes in the
path via signalling. The work in-progress document
[I-D.liu-lsr-mpls-inspection-msd] defines the mechanism to signal
MPLS RLD.
9. Processing the Network Action Sub-Stack
This section defines the specific responsibilities for nodes along an
LSP [RFC3031].
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9.1. Encapsulating Node Responsibilities
The encapsulating node MAY add NASes to the label stack in accordance
with its policies, the placement restrictions in Section 7, and the
capabilities learned from Section 8.
If there is an existing label stack, the encapsulating node MUST NOT
modify the first 20 bits of any LSE in the label stack when the ECMP
technique in the network is using the hashing of the labels on the
label stack.
9.2. Transit Node Responsibilities
The transit node is the node that processes a NAS in the Label stack
but does not push any new NAS.
The transit node MUST follow the procedure for data specified in
Section 5.2.
Transit nodes MUST process the NASes in the label stack, according to
the rules set out in Section 5.5.
A transit node that processes a NAS and does not recognize the value
of an opcode MUST follow the rules according to the setting of the
Unknown Action Handling value in the NAS as described in
(Section 5.4).
9.3. Penultimate Node Responsibilities
In addition to the transit node responsibilities, the penultimate
node and penultimate SR-MPLS segment node MUST NOT remove the last
copy of an HBH or I2E NAS when it is exposed after removing the
forwarding (transport) label. This allows the egress node to process
the NAS.
9.4. Egress Node Responsibilities
The egress node MUST remove any NAS it receives.
10. Network Action Indicator Opcode Definition
The following information MUST be defined for a new Network Action
Indicator opcode request in the document that specifies the Network
Action.
A request for a new NAI opcode MUST include the following
information:
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* Format: The definition of the new Network Action MUST specify the
LSE Formats. The opcode can define Network Action in Format B or
C or both Format B and C. Both Format B and C LSEs MAY optionally
carry Format D LSEs.
* Scope: The definition of the new Network Action MUST specify at
least one scope (I2E, HBH, Select) for the Network Action, and MAY
specify more than one scope.
* Ancillary Data: The definition of the new Network Action MUST
specify the quantity, syntax, and semantics of any associated
Ancillary Data. The Ancillary Data MAY be variable length, but
the NAL MUST be computable based on the data added in the NAS.
* Processing: The definition of the new Network Action MUST specify
the detailed procedure for processing the network action.
* Interactions: The definition of the new Network Action MUST
specify its interaction including merging with other currently
defined Network Action if there is any.
An assignment for a NAI MAY make requests from any combination of the
"Network Action Opcodes" or "Network Action Flags Without Ancillary
Data" assignments. This decision should optimize for eventual
encoding efficiency. If the NAI does not require any ancillary data,
then a flag is preferred as only one bit is used in the encoding.
11. Implementation Status
[Note to the RFC Editor - remove this section before publication, as
well as remove the reference to [RFC7942]]
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
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11.1. University of Tuebingen Implementation
The solution defined in the document draft-ietf-mpls-mna-hdr-08 has
been implemented using P4 pipeline. The implementation code can be
found at https://github.com/uni-tue-kn/P4-MNA. This implementation
uses bSPL value 4 as an MNA label.
12. Security Considerations
The security considerations in [RFC3032] and [RFC9789] also apply to
this document.
In addition, MNA creates a new dimension in security concerns:
* The actions of an encapsulating node can affect any or all of the
nodes along the path. In the most common and benign situations,
such as a syntactically incorrect packet could result in packet
loss or corruption.
* The semantics of a network action are unbounded and may be
insecure. A network action could be defined that made arbitrary
changes to the memory of the forwarding router, which could then
be used by the encapsulating node to compromise every MNA-capable
router in the network.
* The MNA architecture supports locally-defined network actions.
For such actions, there will be limited oversight to ensure that
the semantics do not create security issues. Implementors and
network operators will need to ensure that even the locally-
defined network actions do not compromise the security of the
network by following the security considerations specified in this
document.
* The MPLS domain border nodes MUST ensure that the MPLS packets
with MNA from any domain with a different administrative control
can be filtered to prevent entering the provider MPLS domain. The
filtering capability MAY be enabled on a per network action basis
and it can be based on a local policy. The filtering capability
MUST be implemented on those nodes before deploying MNA in the
provider MPLS domain. The RLD on the filtering node MUST be
higher than the RLD on all other nodes in the provider MPLS
domain.
* The MNA architecture supports modifying the AD on the intermediate
nodes, so the critical network functions should either not rely on
the data or should be aware of the risks and use other means to
verify the security of the whole network.
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* The "private Use" opcodes in "Network Action Opcodes" Section 14.4
and "Network Action Flags Without Ancillary Data" Section 14.3
Registry are subject to the considerations described in [RFC8126].
* System designers must be aware that information included in
Ancillary Data may be transmitted "in the clear." Network actions
that require the exchange of sensitive data, must be defined in
such a way that the data is encrypted in transit. Otherwise,
sensitive data MUST NOT be transmitted using these mechanisms.
* Mis-delivery of a packet due to malformed forwarding action data
could be considered a security risk.
13. Operational Considerations
13.1. Manageability Considerations
An MNA implementation MAY collect the following counters:
* Packets with MNA received
* MNA sub-stacks processed
* MNA per-network-action counters
* Packets with MNA dropped due to unknown actions
* Packets with MNA skipped due to unknown actions
* Packets with MNA dropped due to malformed NAS
Additionally, tracking both successful invocations and failures for
each specific Network Action, are RECOMMENDED to provide granular
visibility. Nodes MAY generate rate-limited notifications or alarms
for significant operational events, such as sustained high rates of
MNA packet drops, frequent encounters of malformed MNA sub-stacks, to
alert operators to potential issues. Comprehensive logging of MNA
processing details and outcomes can aid in the network diagnostics
and post-mortem analysis.
13.2. Performance and Scale Considerations
The considerations for performance and scale assessments are outside
the scope of this document but are encouraged to be addressed in the
MNA application documents.
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13.3. Backward Compatibility
This section discusses interactions between MNA-capable and MNA-
incapable nodes.
An MNA-encapsulating node MUST ensure that the MPLS Network Action
Sub-Stack indicator is not at the top of the MPLS label stack when
the packet arrives at an MNA-incapable node. If such a packet did
arrive at an MNA-incapable node, it will most likely be dropped as
described in Section 2.1.1 of [RFC7325].
Any node could scan the label stack, potentially looking for a label
value containing a bSPL. To ensure that the LSE formats described
herein do not appear to contain a bSPL value, the opcode value of 0
has been reserved. By ensuring that there is a non-zero value in the
high order 7 bits, we are assured that the high order 20 bits cannot
be misinterpreted as containing a bSPL value (0-15).
The TC and TTL values of the Format A LSE are not re-purposed for
encoding, as the penultimate node on the MPLS packet path may
propagate TTL from the transport (or forwarding) label to the next
label on the label stack, overwriting the TTL on the next label. If
the penultimate node is a legacy node, it might perform this action,
potentially corrupting other values stored in the TC and TTL values.
To protect against this, we retain the TC and TTL values in the
Format A LSE.
When adding the Entropy Label Indicator (ELI) (bSPL 7) and Entropy
Label (EL) as defined in [RFC6790], along with an MNA NAS, the RLD
MUST be considered for the placement of both, and they both can be
placed in any order. If a transit LSR chooses to use as much of the
whole label stack as feasible as keys for the load-balancing
function, the MNA reserved label MUST NOT be used as a key for the
load-balancing function, as specified in Section 4.3 of [RFC6790].
Note that the behavior of an MNA-incapable transit LSR that scans the
label stack for ELI and EL but encounters a different, unrecognized
reserved label first, is not modified by this document.
Similarly, when adding the Flow-ID Label Indicator (FLI) (including
the extension label 15) and Flow-ID Label (FL) as defined in
[RFC9714], along with an MNA NAS, the RLD MUST be considered for the
placement of both, and they both can be placed in any order. Note
that the behavior of an MNA-incapable transit LSR that scans the
label stack for FLI (including the extension label 15) and FL, but
encounters a different, unrecognized reserved label first, is not
modified by this document.
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However, as the existing behavior is not specified for transit LSRs,
upon encountering any unrecognized bSPLs or eSPLs below the top of
the label stack, some existing implementations may have chosen to
implement non-standardized actions, such as discarding packets. Any
uses of a new bSPL or eSPL would cause issues with such existing
implementations using the non-standardized actions upon encountering
unrecognized bSPLs or eSPLs below the top of the label stack. Since
this is a generic problem, any clarifications for the treatment of
unrecognized bSPL or eSPL are outside the scope of this document.
14. IANA Considerations
14.1. MNA bSPL Label
This document requests that IANA allocate a value (TBA) for the MNA
bSPL label from the "Base Special-Purpose MPLS Label Values" registry
to indicate the presence of an MNA Sub-Stack in the label stack. The
description of the value should be "MPLS Network Actions". The
reference should be this document.
14.2. MPLS Network Actions Parameters
This document requests that IANA create a new registry group called
"MPLS Network Actions Parameters" within the "Multiprotocol Label
Switching Architecture (MPLS)" category. The registries described
below should belong to this new registry group.
14.3. Network Action Flags Without Ancillary Data
This document requests that IANA create a new registry with the name
"Network Action Flags Without Ancillary Data". Registration requests
should comply with Section 10. The registration procedure for this
registry is "IETF Review", "Experimental Use" and "Private Use" as
defined in [RFC8126]. The fields in this registry are "Bit Position"
(integer), "Description" (string), and "Reference" (string).
Bit Position refers to the position relative to the most significant
bit in LSE Format B or C Data fields and any subsequent Format D
LSEs. Bit Position 0 is the most significant bit in an LSE Format B
or C Data field. Bit Position 20 is the most significant bit in the
first LSE Format D Data field. There are 20 bits available in LSE
Format C and 30 bits available in LSE Format D. There are at most 14
Format D LSEs per opcode (due to NASL limit of 15 and Format D
requires Format C LSE), so there are at most 20 + 14 * 30 = 440 bit
positions. The Bit Position is an integer with value 0-439.
The registration procedures for the code points allocation for this
registry are defined in Table 4:
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+==============+==================+===============+
| Bit Position | Description | Reference |
+==============+==================+===============+
| 0-14 | IETF Review | This document |
+--------------+------------------+---------------+
| 15-16 | Experimental Use | This document |
+--------------+------------------+---------------+
| 17-19 | Private Use | This document |
+--------------+------------------+---------------+
| 20-439 | IETF Review | This document |
+--------------+------------------+---------------+
Table 4: Network Action Flags Without Ancillary
Data Registry
14.4. Network Action Opcodes
This document requests that IANA create a new registry with the name
"Network Action Opcodes". Registration requests should comply with
Section 10 as well as security review. The registration procedure
for this registry is "IETF Review", "Experimental Use" and "Private
Use" as defined in [RFC8126]. The fields are "Opcode" (integer),
"Description" (string), and "Reference" (string). Opcode is an
integer with value 1-126.
+=========+==================+===============+
| Opcode | Description | Reference |
+=========+==================+===============+
| 1-110 | IETF Review | This document |
+---------+------------------+---------------+
| 111-114 | Experimental Use | This document |
+---------+------------------+---------------+
| 115-126 | Private Use | This document |
+---------+------------------+---------------+
| 127 | IETF Review | This document |
+---------+------------------+---------------+
Table 5: Network Action Opcodes Registry
IANA has allocated values for the following Network Action Opcodes
from the "Network Action Opcodes" registry.
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+========+===========================+===============+
| Opcode | Description | Reference |
+========+===========================+===============+
| 0 | Reserved | This document |
+--------+---------------------------+---------------+
| 1 | Flag-Based Network Action | This document |
| | Indicators without AD | |
+--------+---------------------------+---------------+
| 2 | No operation Opcode | This document |
+--------+---------------------------+---------------+
| 127 | Opcode Range Extension | This document |
| | Beyond 127 | |
+--------+---------------------------+---------------+
Table 6: Network Action Opcodes
15. References
15.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC3270] Le Faucheur, F., Ed., Wu, L., Davie, B., Davari, S.,
Vaananen, P., Krishnan, R., Cheval, P., and J. Heinanen,
"Multi-Protocol Label Switching (MPLS) Support of
Differentiated Services", RFC 3270, DOI 10.17487/RFC3270,
May 2002, <https://www.rfc-editor.org/info/rfc3270>.
[RFC3443] Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing
in Multi-Protocol Label Switching (MPLS) Networks",
RFC 3443, DOI 10.17487/RFC3443, January 2003,
<https://www.rfc-editor.org/info/rfc3443>.
[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, February
2009, <https://www.rfc-editor.org/info/rfc5462>.
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[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC9017] Andersson, L., Kompella, K., and A. Farrel, "Special-
Purpose Label Terminology", RFC 9017,
DOI 10.17487/RFC9017, April 2021,
<https://www.rfc-editor.org/info/rfc9017>.
[RFC9789] Andersson, L., Bryant, S., Bocci, M., and T. Li, "MPLS
Network Actions (MNAs) Framework", RFC 9789,
DOI 10.17487/RFC9789, July 2025,
<https://www.rfc-editor.org/info/rfc9789>.
15.2. Informative References
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<https://www.rfc-editor.org/info/rfc3031>.
[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, June 2011,
<https://www.rfc-editor.org/info/rfc6291>.
[RFC7325] Villamizar, C., Ed., Kompella, K., Amante, S., Malis, A.,
and C. Pignataro, "MPLS Forwarding Compliance and
Performance Requirements", RFC 7325, DOI 10.17487/RFC7325,
August 2014, <https://www.rfc-editor.org/info/rfc7325>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
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[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
[RFC9613] Bocci, M., Ed., Bryant, S., and J. Drake, "Requirements
for Solutions that Support MPLS Network Actions (MNAs)",
RFC 9613, DOI 10.17487/RFC9613, August 2024,
<https://www.rfc-editor.org/info/rfc9613>.
[RFC9714] Cheng, W., Ed., Min, X., Ed., Zhou, T., Dai, J., and Y.
Peleg, "Encapsulation for MPLS Performance Measurement
with the Alternate-Marking Method", RFC 9714,
DOI 10.17487/RFC9714, February 2025,
<https://www.rfc-editor.org/info/rfc9714>.
[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, July 2025,
<https://www.rfc-editor.org/info/rfc9791>.
[I-D.liu-lsr-mpls-inspection-msd]
Liu, Y., "Signaling MPLS Readable Label Depth(RLD)", Work
in Progress, Internet-Draft, draft-liu-lsr-mpls-
inspection-msd-04, 18 September 2023,
<https://datatracker.ietf.org/doc/html/draft-liu-lsr-mpls-
inspection-msd-04>.
Appendix A. Examples
A.1. Network Action Encoding Examples
A.1.1. Network Action Flags without AD
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=bSPL | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=1 | 13-bit Flags |R|IHS|S|NASL=0 |U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: NAS with Network Action Flags
This is an example of a NAS with Flag-Based NAIs without Ancillary
Data.
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Details:
Opcode=1: This opcode to indicates that the LSE carries Flag-Based
NAIs without AD.
Data: The data field carries the Flag-Based NAIs.
S: This is the bottom of stack bit. Set if and only if this LSE
is the bottom of the stack.
U: Action to be taken if one of the NAIs are not recognized by the
processing node.
NASL: The NASL value is set to 0, as there are no additional LSEs.
NAL: The NAL value is set to 0, as there are no additional AD
encoded using Format D.
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=bSPL | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | Data=0 |R|IHS|S|NASL=2 |U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=1 | Flag-Based NAIs |S| NAIs |U|NAL=1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Additional Flag-Based NAIs |S|Flag-Based-NAIs|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Network Action Flags without AD using LSE Format D
In this example, the NAS contains a Format B LSE with No-Operation
Opcode value 2. The next LSE uses Format C, but the Network Action
Flag is not in a bit position contained within the Format C LSE, so a
single Format D LSE has been added to the NAS to carry the flag.
NAL is set to 1 to indicate that Flag-Based NAIs are also encoded in
the next LSE.
NASL is set to 2 to indicate that 2 additional LSEs are used.
A.1.2. Network Action Opcode with AD
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-Label=bSPL | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=8 | Ancillary Data |R|IHS|S|NASL=0 |U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Network action opcode with Ancillary Data
In this example, the NAS is carrying only one Network Action that
requires 13 bits of Ancillary Data.
Details on the Second LSE
Opcode=8: A network action allocation is outside of this document.
Data: The data field contains 13 bits of ancillary data.
A.1.3. Network Action Opcode with more AD with Format-B
A network action may require more Ancillary Data than can fit in a
single LSE. In this example, a Format D LSE is added to carry
additional Ancillary Data.
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=bSPL | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=10 | Ancillary Data |R|IHS|S|NASL=1 |U|NAL=1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Ancillary Data |S|Ancillary Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Network Action With Additional Ancillary Data
In this example, opcode 10 is encoded in Format B and it requires
more than one LSE's worth of Ancillary Data, so a Format D LSE is
added.
Details on the second LSE:
Opcode=10: An opcode allocation is outside of this document.
Ancillary Data: Ancillary data required to process the Network
Action opcode 10.
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NAL: Length of additional LSEs used to encode its Ancillary data.
Details on the third LSE:
Ancillary Data: 22 bits of additional Ancillary data.
Ancillary Data: 8 bits of additional Ancillary Data.
A.1.4. Network Action Opcode with more AD with Format C
A network action may require more Ancillary Data than can fit in a
single LSE. In this example, a Format D LSE is added to carry
additional Ancillary Data.
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=bSPL | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | Data=0 |R|IHS|S|NASL=2 |U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=9 | Ancillary Data |S| AD |U|NAL=1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Ancillary Data |S|Ancillary Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Network Action With Additional Ancillary Data
In this example, opcode 9 requires more than one LSE's worth of
Ancillary Data, so a Format D LSE is added.
Details on the third LSE:
Opcode=9: An opcode allocation is outside of this document
Ancillary Data: Most significant bits of Ancillary data
AD: 4 bits of additional Ancillary Data
Details on the fourth LSE:
Ancillary Data: 22 bits of additional Ancillary data.
Ancillary Data: 8 bits of additional Ancillary Data.
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A.2. Network Action Processing Order
The semantics of a network action can vary widely and the results of
processing one network action may affect the processing of a
subsequent network action. See Section 5.5.
A.2.1. Network Action Processing Order
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=bSPL | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=8 | Ancillary Data |R|IHS|S|NASL=2 |U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=7 | Ancillary Data7 |S| AD7 |U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=1 | Flag-Based NAIs |S| NAI |U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: In-stack NA processing order
In this example, opcode 8 is processed first, then opcode 7, and then
the network action flags are processed from most significant to least
significant.
In a different case, some Flag-Based NAIs may need to be processed
before opcode 7 and some Flag-Based NAIs may need to be processed
after Opcode 7. This can be done by causing some NAIs to appear
earlier in the 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=bSPL | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=8 | Ancillary Data |R|IHS|S|NASL=3 |U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=1 | 0x01 |S| NAI |U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=7 | Ancillary Data7 |S| AD7 |U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=1 | 0x02 |S| NAI |U|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: Interleaving network actions
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In the above example, opcode 8 is processed first, then Flag-Based
NAI 0x01 is processed, then opcode 7 is processed, and finally NAI
0x02 is processed.
Acknowledgments
The authors of this document would like to thank the MPLS Working
Group Open Design Team for the discussions and comments on this
document. The authors would also like to thank Amanda Baber for
reviewing the IANA Considerations and providing many useful
suggestions. The authors would like to thank Loa Andersson, Stewart
Bryant, Greg Mirsky, Joel M. Halpern and Adrian Farrel for reviewing
this document and providing many useful suggestions. The authors
would like to thank Fabian Ihle and Michael Menth, both from
University of Tuebingen, for reviewing and implementing the solution
defined in this document in P4 pipeline. Also, thank you, Tarek Saad
for the Shepherd's review, Joe Clarke for OpsDir review, Matthew
Bocci for Rtgdir review, Derrell Piper for Secdir review, and James
Guichard for the AD review, Mohamed Boucadair, Eric Vyncke, Deb
Cooley, Ketan Talaulikar, Mahesh Jethanandani for IESG review, which
helped improve this document.
Contributors
The following people have substantially contributed to this document:
Jisu Bhattacharya
Cisco Systems, Inc.
Email: jisu@cisco.com
Bruno Decraene
Orange
Email: bruno.decraene@orange.com
Weiqiang Cheng
China Mobile
Email: chengweiqiang@chinamobile.com
Xiao Min
ZTE Corp.
Email: xiao.min2@zte.com.cn
Luay Jalil
Verizon
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Email: luay.jalil@verizon.com
Jie Dong
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: jie.dong@huawei.com
Tianran Zhou
Huawei Technologies
China
Email: zhoutianran@huawei.com
Bin Wen
Comcast
Email: Bin_Wen@cable.comcast.com
Sami Boutros
Ciena
Email: sboutros@ciena.com
Tony Li
Juniper Networks
United States
Email: tony.li@tony.li
John Drake
Juniper Networks
United States
Email: jdrake@juniper.net
Figure 13
Authors' Addresses
Jaganbabu Rajamanickam (editor)
Cisco Systems, Inc.
Canada
Email: jrajaman@cisco.com
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Rakesh Gandhi (editor)
Cisco Systems, Inc.
Canada
Email: rgandhi@cisco.com
Royi Zigler
Broadcom
Email: royi.zigler@broadcom.com
Haoyu Song
Futurewei Technologies
Email: haoyu.song@futurewei.com
Kireeti Kompella
Juniper Networks
United States
Email: kireeti.ietf@gmail.com
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