[mpls] Re: draft-ietf-mpls-mna-hdr-17 ietf last call Rtgdir review

["Matthew Bocci (Nokia)" <[e-mail]>]

Hi Jags

Thank you for considering my comments and updating the draft. I am good with all the resolutions.

Best regards

Matthew

From: Jaganbabu Rajamanickam (jrajaman) <[e-mail]>
Date: Tuesday, 13 January 2026 at 12:35
To: Matthew Bocci (Nokia) <[e-mail]>, [e-mail] <[e-mail]>
Cc: [e-mail] <[e-mail]>, [e-mail] <[e-mail]>, [e-mail] <[e-mail]>
Subject: Re: draft-ietf-mpls-mna-hdr-17 ietf last call Rtgdir review

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Hello Matthew,
   Thanks for your feedback.
   We have updated the draft with your feedback.
   We are attaching the diff  and the our response to your feedback.

   Please let us know if you have any questions.

Thanx,
Jags


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From: Matthew Bocci via Datatracker <[e-mail]>
Date: Friday, December 19, 2025 at 11:38 AM
To: [e-mail] <[e-mail]>
Cc: [e-mail] <[e-mail]>, [e-mail] <[e-mail]>, [e-mail] <[e-mail]>
Subject: draft-ietf-mpls-mna-hdr-17 ietf last call Rtgdir review

Document: draft-ietf-mpls-mna-hdr
Title: MPLS Network Action (MNA) Sub-Stack Solution
Reviewer: Matthew Bocci
Review result: Has Issues

Hello,

I have been selected as the Routing Directorate reviewer for this draft. The
Routing Directorate seeks to review all routing or routing-related drafts as
they pass through IETF last call and IESG review, and sometimes on special
request. The purpose of the review is to provide assistance to the Routing ADs.
For more information about the Routing Directorate, please see
https://wiki.ietf.org/en/group/rtg/RtgDir

Although these comments are primarily for the use of the Routing ADs, it would
be helpful if you could consider them along with any other IETF Last Call
comments that you receive, and strive to resolve them through discussion or by
updating the draft.

Document: draft-ietf-mpls-mna-hdr-17
Reviewer: Matthew Bocci
Review date: 18-12-2025

Summary
-------
In general, the draft is clear and readable. Thank you!
I appreciate that the draft is the a part of a wider set of protocol extensions
required to achieve MPLS Network Actions, so I have primarily reviewed this
from the context of the header format and processing that it defines, rather
than broader questions of the overall trajectory of the MNA design. I believe
my comments are fairly minor but these should be resolved before progressing
the draft.

Detailed Comments.
-----------------
Comments are embedded below, prefixed by MB>. Line numbers are generated by
id-nits.

2       MPLS Working Group                                  J. Rajamanickam, Ed.
3       Internet-Draft                                            R. Gandhi, Ed.
4       Intended status: Standards Track                     Cisco Systems, Inc.
5       Expires: 4 June 2026                                           R. Zigler
6                                                                       Broadcom
7                                                                        H. Song
8                                                         Futurewei Technologies
9                                                                    K. Kompella
10                                                              Juniper Networks
11                                                               1 December 2025

13                    MPLS Network Action (MNA) Sub-Stack Solution
14                             draft-ietf-mpls-mna-hdr-17

MB> Can the title of the document better reflect its content? The draft
specifies the MNA Sub-stack, including support for in-stack data, but not
support for post-stack data. Also, it is not an MNA solution as described in
RFC9782 Section 2, but is primarily a header specification. I would suggest
updating the title to something like: "MPLS Network Action (MNA) Sub-Stack
Specification including In-Stack Network Action Indicators and In-Stack Data.",
or something along those lines.

16      Abstract

18         This document defines the MPLS Network Actions (MNA) sub-stack
19         solution for carrying Network Actions and Ancillary Data in the MPLS
20         label stack.  MNA can be used to influence packet forwarding
21         decisions, carry additional Operations, Administration, and
22         Maintenance information in the MPLS packet or perform user-defined
23         operations.  The solution specified in this document addresses the
24         requirements for In-stack network action and In-stack data found in
25         RFC 9613.  This document follows the architectural framework for the

MB> I suggest re-phrasing to:

8          This document specifies the MPLS Network Actions (MNA) sub-stack
19         for carrying Network Actions and Ancillary Data in the MPLS
20         label stack.  MNA can be used to influence packet forwarding
21         decisions, carry additional Operations, Administration, and
22         Maintenance information in the MPLS packet or perform user-defined
23         operations.  This document addresses the
24         requirements for In-stack network actions and In-stack data found in
25         RFC 9613.

[snip]

115     1.  Introduction

117        [RFC3032] defines the encoding of the MPLS label stack, the basic
118        structure used to define a forwarding path.  Forthcoming applications

MB> The term "forthcoming" could become outdated very rapidly. Rather than
saying "Forthcoming applications" it would be clearer to move the reference to
RFC9791 up front and say "There are applications that... ".

119        require MPLS packets to perform special network actions and carry
120        optional Ancillary Data (AD) that can affect the packet forwarding
121        decision or trigger Operations, Administration, and Maintenance (OAM)
122        logging, for example.  Ancillary Data can be used to carry additional
123        information, such as a network slice identifier or an entropy value
124        for load-balancing.  Several MPLS Network Actions (MNA) applications
125        are described in [RFC9791].

127        The solution specified in this document addresses the requirements
128        for In-stack network action and In-stack data (ISD) found in
129        [RFC9613].

131        This document defines the syntax and semantics of network actions and
132        ancillary data encoded in an MPLS label stack.  In-stack actions and
133        ancillary data are contained in a Network Action Sub-Stack (NAS),
134        which is recognized by a new base Special Purpose Label (bSPL).  This
135        document follows the framework specified in [RFC9789].

[snip]

201     3.  Overview

203        The MPLS Network Action Sub-Stack (NAS) is a set of Label Stack
204        Entries (LSEs) that appear as part of an MPLS label stack and serve
205        to encode information about the network actions that should be
206        invoked for the packet.  Multiple NASes may appear in a label stack
207        and be placed as described in Section 5.

209        This document describes how network actions and their optional
210        ancillary data are encoded as part of an NAS as a stack of LSEs.

MB> s/an NAS/a NAS
MB> I think it is worth adding a statement that this document defines new LSE
formats beyond RFC3032 that define behaviors or are processed in different ways
to MPLS labels as defined in RFC3031.

211        Mechanisms that allow sharing of ancillary data (AD) between multiple
212        network actions encoded in the same NAS can be described in other
213        documents and do not rely on any explicit provision in the encodings
214        described in this document.

216     4.  Label Stack Entry Formats

218        The NAS uses a variety of different formats of LSEs for different
219        purposes.  This section describes the syntax of the various formats
220        while the overall structure of the NAS and the semantics of the
221        various LSEs are described in the sections below.

223     4.1.  LSE Format A: The MNA Sub-Stack Indicator

225        LSE Format A is an LSE as described in [RFC3032] and [RFC5462].  The
226        label value is an IANA-assigned value (TBA) for the MNA bSPL label
227        from the "Base Special-Purpose MPLS Label Values" registry to
228        indicate the presence of MNA in the packet and the beginning of an
229        MNA Sub-Stack in the label stack.

231         0                   1                   2                   3
232         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
233        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
234        |      MNA-Label=bSPL                   | TC  |S|    TTL        |
235        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

237                 Figure 1: LSE Format A: The MNA Sub-Stack Indicator

239        *  S (1 bit): The Bottom of Stack [RFC3032].  MUST be set to 0 on
240           transmitted packets.  If a packet is received with an LSE
241           containing the bSPL (value TBA) and with S bit set to 1, then the
242           packet MUST be dropped.

244     4.2.  LSE Format B: The initial opcode

246        LSE Format B is used to encode the first opcode in the NAS, plus a
247        number of other fields about the NAS.  This LSE can carry up to 13
248        bits of ancillary data.

250         0                   1                   2                   3
251         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
252        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
253        |   Opcode    |        13-bit Data      |R|IHS|S|  NASL |U| NAL |
254        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

256                      Figure 2: LSE Format B: The initial opcode

258        *  Opcode (7 bits): The operation code for this LSE.  See
259           Section 5.1.

261        *  Data (13 bits): Opcode-specific ancillary data.

263        *  R (1 bit): Reserved.  This bit MUST be transmitted as zero and
264           ignored upon receipt.

MB> Suggest rephrasing to "This bit MUST be set to zero on transmission and
ignored upon receipt." to be more consistent with other MPLS RFCs.

266        *  IHS (2 bits): The scope of the sub-stack.  See Section 5.3.

MB> Isn't this the scope of the network action rather than the sub-stack? That
would be consistent with RFC9613 and Section 5.3.

268        *  S (1 bit): The Bottom of Stack [RFC3032].  If NASL value is non-
269           zero, then S bit MUST be 0.  If a packet is received with S bit
270           set to 1 and a non-zero NASL value, then the packet MUST be
271           dropped.  The encapsulating node MUST ensure that the S bit is set
272           to 1 only in the Last LSE in the MPLS header.

[snip]

338        *  S (1 bit): The Bottom of Stack [RFC3032].  If this is not the last
339           LSE for the Network Action based on the NAL value and if S bit is
340           set to 1 then the packet MUST be dropped.  If this is not the last
341           LSE in the NAS and if S bit is set to 1 then the packet MUST be
342           dropped.  The encapsulating node MUST ensure that the S bit is set
343           to 1 only in the Last LSE.

345        *  Data (22 bits + 8 bits): Opcode-specific ancillary data

MB> Full stop/period is missing at the end of the above bullet.

347        NOTE: A Format A and a Format B LSE MUST be present when a Format D
348        LSE is carried in the NAS.

350     5.  The MNA Sub-Stack

352        The MNA Sub-Stack begins with a Format A LSE (Section 4.1).  The
353        label value of the LSE contains the MNA bSPL (value TBA) to indicate
354        the presence of the MNA Sub-Stack.

[snip]

371        The Format B LSE (Section 4.2) could optionally carry additional data
372        in Format D (Section 4.4) LSEs, up to the length encoded in the LSE's
373        NAL value.

375        An NAS MAY contain more Format C (Section 4.3) and Format D

MB> s/An NAS/A NAS.

376        (Section 4.4) LSEs, up to the length encoded in the NASL value.  All
377        Format D LSEs MUST follow a Format C or B LSE and be included in that
378        LSE's NAL value.

380     5.1.  Opcodes

382        The opcode is a 7-bit field that indicates the semantics of its LSE.
383        Several opcodes are assigned special semantics (Section 6), others
384        act as Network Action Indicators and are assigned through IANA
385        (Section 10 and Section 14.4).

387     5.2.  Ancillary Data

389        The data field carries opcode-specific data that is ancillary data
390        for a network action.  In the case of opcode 1, the data field
391        carries Flag-Based Network Action Indicators without ancillary data.

393        Legacy implementations might use the label value (most significant 20

MB> I am not sure you mean "Leagacy implementations" since this document does
not obsolete RFC3031 or any other RFC. Label based hashing is a perfectly valid
way of ensuring ECMP behavior does not lead to out of order packet delivery on
an MPLS-based service, and it is very widely deployed. Maybe rephrase to: "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."

394        bits) in one or more consecutive LSEs when load-balancing data flows
395        in an ECMP environment.  Modifying the first 20 bits in an LSE might
396        alter that packet's path and result in out-of-order delivery of
397        packets.  To maintain the stability of deployed services in ECMP

MB> The sentence above doesn't quite capture what it is trying to say, I think.
I suggest modifying to: "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."

398        environments that rely on label value information for load-balancing,
399        care must be taken when encoding network action data in the given
400        LSE.  If the network action data may differ among packets in the same
401        flow or change during forwarding across the MPLS network, it MUST NOT
402        be placed in the most significant 20 bits of a Format B LSE
403        (Section 4.2), a Format C LSE (Section 4.3), or a Format D LSE
404        (Section 4.4).  Thus, the available bits for data that can change by
405        a transit node or differ among packets of the same flow in Format A
406        and Format B LSEs are 0, Format C LSE is 7 (bits 20-22 and 25-28) and
407        Format D LSE is 11 (bits 20-22 and 24-31).

[snip]

426     5.3.  Scope

428        The IHS field in the Format B LSE indicates the scope of all the NAIs
429        encoded in the NAS.  Scope defines which nodes along the MPLS path
430        should perform the network actions found within the NAS.  The
431        specific values of the IHS field are as follows:

433                         +======+=========================+
434                         | Bits | Scope                   |
435                         +======+=========================+
436                         | 00   | I2E                     |
437                         +------+-------------------------+
438                         | 01   | HBH                     |
439                         +------+-------------------------+
440                         | 10   | Select                  |
441                         +------+-------------------------+
442                         | 11   | Reserved for future use |
443                         +------+-------------------------+

445                             Table 2: IHS Scope Values

447           Ingress To Egress (I2E) - The NAS MUST NOT be processed by any
448           node except the egress node.

MB> Is it the NAS or the network action (or NAI) that is scoped? The
terminology in RFC9789 seems to suggest that it is the NA. I suggest aligning
the definitions in this section with that RFC.

450           Hop-By-Hop (HBH) - All nodes along the path MUST process the NAS.

452           Select - Only specific nodes along the path that brings NAS to top
453           of the stack will perform the action.

455        A single NAS carries only one of the three scopes (I2E/HBH/Select).
456        To support multiple scopes for a single packet, multiple NASes MAY be
457        included in a single label stack.

MB> Ah OK. So now you say it is the NAS that is scoped. Would it be more recise
to say that a given NAS can only carry NAIs with the same scope?

459        The egress node is included in the HBH scope.  This implies that the
460        penultimate node MUST NOT remove a HBH NAS.  The egress node MAY
461        receive an NAS at the top of the label stack as discussed in
462        Section 10.

464        An I2E scope NAS, if present, MUST be encoded after any HBH or
465        Select-scope NASes.  This makes it easier for the transit nodes to
466        process a NAS with HBH or Select scope.

468        If a packet is received with the IHS scope set to "Reserved for
469        future use", the packet is processed based on the U bit in the Format
470        B LSE in the NAS.

[snip]

565     7.  NAS placement in the Label Stack

567        The node adding an NAS to the label stack places a copy of the NAS
568        where the relevant nodes can read it.  Each downstream node along the
569        path has a Readable Label Depth (RLD).  If the NAS is to be processed
570        by a downstream MNA-capable node, then the entire NAS MUST be placed
571        so that it is within RLD by the time the packet reaches the
572        downstream MNA-capable node.

574        If the label stack is deep, several copies of the NAS may need to be
575        encoded in the label stack.

577        For an NAS with HBH scope, every node will process the top copy of

MB> s/an NAS/a NAS

578        the NAS, but the NAS MUST NOT appear at the top of the stack at any
579        MNA-incapable node on the path.

581        An NAS MUST NOT appear at the top of the stack after popping the
582        forwarding label on an MNA-incapable node on the path.

MB> Can you provide more guidance on how the MNA capable inress LER can ensure
this if the downstream node is MNA incapable?

584        The node behaviour, where an NAS with I2E and HBH scopes is also
585        removed along with popping the forwarding label on a PHP node, is
586        outside the scope of this document.

588        For an NAS with Select scope, it is processed by the node that brings

MB> s/an NAS/a NAS

589        it to the top of stack (for example, in the case of using MPLS label
590        pop operation in Segment Routing) and then the NAS is removed from
591        the stack.  The select-scoped NAS needs to be inserted after the
592        forwarding label and before the next forwarding label.  It could be
593        inserted before or after a HBH NAS.  Note that the case of an NAS
594        with Select scope with MPLS label swap operation (for example, with
595        RSVP Traffic Engineering LSPs) is for future study.

[snip]

614     7.1.  Actions when Pushing Labels

616        An MNA-capable node may need to push additional labels as well as
617        push new network actions onto a received packet.

619        While pushing additional labels on to the label stack of the received
620        packet, the MNA-capable node MUST verify that the entire top-most NAS
621        with HBH scope is still within the RLD of the downstream MNA-capable
622        nodes.  If required, the MNA-capable node MAY create a copy of the
623        top-most NAS with HBH scope and insert it within the RLD of the
624        downstream MNA-capable nodes on the label stack.

626        When an MNA-capable node needs to push a new NAS with HBH scope on to
627        a received packet that already has an NAS with HBH scope, it SHOULD
628        copy (and merge) the network actions (including their Ancillary Data)
629        from the received top-most NAS with HBH scope in the new NAS with HBH
630        scope.  The new NAS MUST be placed within the RLD of the downstream
631        MNA-capable nodes.  This behavior can be based on local policy.

633        The new network actions added MUST NOT conflict with the network
634        actions in the received NAS with HBH scope.  The mechanism to resolve
635        such conflicts depend on the network actions and can be based on
636        local policy.  The MNA-capable node that pushes entries MUST
637        understand any network actions which it is pushing which may result
638        in a conflict, and MUST resolve any conflicts between new and
639        received network actions.  In the usual case of a conflict of
640        duplicating a network action, the definition of the network action
641        will generally give guidance on likely resolutions.

MB> The last sentence above is unclear. Also, I think this should be more
prescriptive so that such that the resolution of conflicts is deterministic. I
propose rephrasing to "The definition of a network action MUST give guidance on
confict resolution."

643     8.  Node Capability Signaling

645        The Encapsulating Node is the node that pushes an NAS on to the Label
646        stack.

MB> 'encapsulating node' to be consistent wiht the captulaisation below.

648        The encapsulating node MUST make sure that the NAS can be processed
649        by the transit and egress nodes.

651        *  The node responsible for selecting a path through the MPLS network
652           needs to know and consider the MNA-capabilities and RLD of the
653           transit nodes, and the MNA-capabilities of the end point.

655        *  Information about the capabilities of the nodes may be configured,
656           collected through management protocols, or distributed by control
657           protocols (such as advertising by routing protocols).

659        *  The mechanisms by which the capabilities of the nodes are known by
660           the node responsible for selecting a path through the MPLS network
661           are out of scope for this document.

663        *  In the case of MPLS Segment Routing (SR-MPLS), as well as the,
664           RLD, the path computation system needs to know the MSD [RFC8664]
665           that can be imposed at the ingress node of a given SR path.  This
666           ensures that the label stack depth of a computed path does not
667           exceed the maximum number of labels (i.e., MSD) the node is
668           capable of imposing and the maximum number of labels that can be
669           read by the MNA-processing nodes in the path.  The MSD needs to
670           include the MNA Sub-Stacks to be added.

MB> I think this is 'MUST include'.

672     9.  Processing the Network Action Sub-Stack

674        This section defines the specific responsibilities for nodes along an
675        LSP [RFC3031].

677     9.1.  Encapsulating Node Responsibilities

679        The encapsulating node MAY add NASes to the label stack in accordance
680        with its policies, the placement restrictions in Section 7, and the
681        limitations learned from Section 8.

683        The encapsulating node MUST NOT add an NAS to the label stack if the
684        egress node does not support MNA.

MB> s/an NAS/a NAS

686        If there is an existing label stack, the encapsulating node MUST NOT
687        modify the first 20 bits of any LSE in the label stack when the ECMP
688        technique in the network is using the hashing of the labels on the
689        label stack.

691        If the encapsulating node is also a transit node, then it MUST also
692        follow the rules set out in Section 9.2.

[snip]

724        The following information MUST be defined for a new Network Action
725        Indicator opcode request in the document that specifies the Network
726        Action.

728        A request for a new NAI opcode MUST include the following
729        information:

731        *  Format: The definition of the new Network Action MUST specify the
732           LSE Formats.  The opcode can define Network Action in Format B or
733           C or both Format B and C.  Both Format B and C LSEs MAY optionally
734           carry Format D LSEs.

736        *  Scope: The definition of the new Network Action MUST specify at
737           least one scope (I2E, HBH, Select) for the Network Action, and MAY
738           specify more than one scope.

740        *  Ancillary Data: The definition of the new Network Action MUST
741           specify the quantity, syntax, and semantics of any associated
742           Ancillary Data.  The Ancillary Data MAY be variable length, but
743           the length MUST be computable based on the data present in the
744           NAS.

746        *  Processing: The definition of the new Network Action MUST specify
747           the detailed procedure for processing the network action.

749        *  Interactions: The definition of the new Network Action MUST
750           specify its interaction with other currently defined Network
751           Action if there is any.

MB> Including any considerations in merging network actions?

753        An assignment for an NAI MAY make requests from any combination of
754        the "Network Action Opcodes" or "Network Action Flags Without
755        Ancillary Data" assignments.  This decision should optimize for
756        eventual encoding efficiency.  If the NAI does not require any
757        ancillary data, then a flag is preferred as only one bit is used in
758        the encoding.

760     11.  Backward Compatibility

762        This section discusses interactions between MNA-capable and legacy,
763        MNA-incapable nodes.

MB> remove the work 'legacy' in this section as suggested above. It is just
'MNA-incapable'.

765        An MNA-encapsulating node MUST ensure that the MPLS Network Action
766        Sub-Stack indicator is not at the top of the MPLS label stack when
767        the packet arrives at an MNA-incapable node.  If such a packet did
768        arrive at an MNA-incapable node, it will most likely be dropped as
769        described in Section 2.1.1 of [RFC7325].

771        Legacy nodes may scan the label stack, potentially looking for a
772        label value containing a bSPL.  To ensure that the LSE formats

MB> *any* node cold scan the label stack looking for a bSPL.

773        described herein do not appear to contain a bSPL value, the opcode
774        value of 0 has been reserved.  By ensuring that there is a non-zero
775        value in the high order 7 bits, we are assured that the high order 20
776        bits cannot be misinterpreted as containing a bSPL value (0-15).

778        The TC and TTL values of the Format A LSE are not re-purposed for
779        encoding, as the penultimate node on the MPLS packet path may
780        propagate TTL from the transport (or forwarding) label to the next
781        label on the label stack, overwriting the TTL on the next label.  If
782        the penultimate node is a legacy node, it might perform this action,
783        potentially corrupting other values stored in the TC and TTL values.
784        To protect against this, we retain the TC and TTL values in the
785        Format A LSE.

787        When adding the Entropy Label Identifier (ELI) (bSPL 7) and Entropy

MB> Entropy Label Identifier / Entropy Label Indicator

788        Label (EL) as defined in [RFC6790], along with an MNA NAS, the RLD
789        MUST be considered for the placement of both, and they both can be
790        placed in any order.  If a transit LSR chooses to use as much of the
791        whole label stack as feasible as keys for the load-balancing
792        function, the MNA reserved label MUST NOT be used as a key for the
793        load-balancing function, as specified in Section 4.3 of [RFC6790].
794        Note that the behavior of an MNA-incapable transit LSR that scans the
795        label stack for ELI and EL but encounters a different, unrecognized
796        reserved label first, is not modified by this document.

798        Similarly, when adding the Flow-ID Label Indicator (FLI) (including
799        the extension label 15) and Flow-ID Label (FL) as defined in
800        [RFC9714], along with an MNA NAS, the RLD MUST be considered for the
801        placement of both, and they both can be placed in any order.  Note
802        that the behavior of an MNA-incapable transit LSR that scans the
803        label stack for FLI (including the extension label 15) and FL, but
804        encounters a different, unrecognized reserved label first, is not
805        modified by this document.

807        However, as the existing behavior is not specified for transit LSRs,
808        upon encountering any unrecognized bSPLs or eSPLs below the top of
809        the label stack, some existing implementations may have chosen to
810        implement non-standardized actions, such as discarding packets.  Any
811        uses of a new bSPL or eSPL would cause issues with such existing
812        implementations using the non-standardized actions upon encountering
813        unrecognized bSPLs or eSPLs below the top of the label stack.  Since
814        this is a generic problem, any clarifications for the treatment of
815        unrecognized bSPL or eSPL are outside the scope of this document.

817     12.  Implementation Status

819        [Note to the RFC Editor - remove this section before publication, as
820        well as remove the reference to [RFC7942]]

822        This section records the status of known implementations of the
823        protocol defined by this specification at the time of posting of this
824        Internet-Draft, and is based on a proposal described in [RFC7942].
825        The description of implementations in this section is intended to
826        assist the IETF in its decision processes in progressing drafts to
827        RFCs.  Please note that the listing of any individual implementation
828        here does not imply endorsement by the IETF.  Furthermore, no effort
829        has been spent to verify the information presented here that was
830        supplied by IETF contributors.  This is not intended as, and must not
831        be construed to be, a catalog of available implementations or their
832        features.  Readers are advised to note that other implementations may
833        exist.

835     12.1.  University of Tuebingen Implementation

837        The solution defined in the document draft-ietf-mpls-mna-hdr-08 has
838        been implemented using P4 pipeline.  The implementation code can be
839        found at https://github.com/uni-tue-kn/P4-MNA.

MB> General comment: It would be useful to record the above implementation
status somewhere public after it is removed from this document. The text should
also be clear as to what value of bSPL is used by this implementation to avoid
the risks of clashes in the wild, since there is no early allocation for the
MNA bSPL.

841     13.  Security Considerations

843        The security considerations in [RFC3032] and [RFC9789] also apply to
844        this document.

846        In addition, MNA-creates a new dimension in security concerns:

848        *  The actions of an encapsulating node can affect any or all of the
849           nodes along the path.  In the most common and benign situations,
850           such as a syntactically incorrect packet could result in packet
851           loss or corruption.

853        *  The semantics of a network action are unbounded and may be
854           insecure.  A network action could be defined that made arbitrary
855           changes to the memory of the forwarding router, which could then
856           be used by the encapsulating node to compromise every MNA-capable
857           router in the network.  The IETF needs to ensure that only secure
858           network actions are defined.

860        *  The MNA architecture supports locally-defined network actions.
861           For such actions, there will be limited oversight to ensure that
862           the semantics do not create security issues.  Implementors and
863           network operators will need to ensure that the locally-defined
864           network actions do not compromise the security of the network.

866        *  The MPLS domain border nodes MUST ensure that the MPLS packets
867           with MNA from any domain with a different administrative control
868           can be filtered to prevent entering the provider MPLS domain.  The
869           filtering capability MAY be enabled on a per network action basis
870           and it can be based on a local policy.  The filtering capability
871           MUST be implemented on those nodes before deploying MNA in the
872           provider MPLS domain.  The RLD on the filtering node MUST be
873           higher than the RLD on all other nodes in the provider MPLS
874           domain.

876        *  The MNA architecture supports modifying the AD on the intermediate
877           nodes, so the critical network functions should either not rely on
878           the data or should be aware of the risks and use other means to
879           verify the security of the whole network.

881        *  The "private Use" opcodes in "Network Action Opcodes" Section 14.4
882           and "Network Action Flags Without Ancillary Data" Section 14.3
883           Registry are subject to the considerations described in [RFC8126].

885        *  System designers must be aware that information included in
886           Ancillary Data may be transmitted "in the clear."  Network actions
887           that require the exchange of sensitive data, must be defined in
888           such a way that the data is encrypted in transit.

MB> MNA can define new forwarding actions. Mis-delivery of a packet due to
malformed forwarding action data could be considered a security risk. I suggest
adding this.

890     14.  IANA Considerations
891     14.1.  MNA bSPL Label

893        This document requests that IANA allocate a value (TBA) for the MNA
894        bSPL label from the "Base Special-Purpose MPLS Label Values" registry
895        to indicate the presence of an MNA Sub-Stack in the label stack.  The
896        description of the value should be "MPLS Network Actions".  The
897        reference should be this document.

899     14.2.  MPLS Network Actions Parameters

901        This document requests that IANA create a new category called "MPLS
902        Network Actions Parameters" within the "Multiprotocol Label Switching
903        Architecture (MPLS)" category.  The registries described below should
904        belong to this new category.

[snip]