MPLS Working Group M. Bocci
Internet-Draft Nokia
Intended status: Informational S. Bryant
Expires: November 6, 2022 University of Surrey 5GIC
May 05, 2022
Requirements for MPLS Network Action Indicators and MPLS Ancillary Data
draft-ietf-mpls-miad-mna-requirements-00
Abstract
This draft specifies requirements for indicators in the MPLS label
stack to support ancillary data in the packet and high level
requirements on that ancillary data. This work is the product of the
IETF MPLS Open Design Team. Requirements are derived from a number
of new proposals for additions to the MPLS label stack to allow
forwarding or other processing decisions to be made, either by a
transit or terminating LSR (i.e. the LER), based on application data
that may be in or below the bottom of the label stack.
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
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on November 6, 2022.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Background . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5
3. MPLS Network Action Indicator Requirements . . . . . . . . . 5
3.1. General Requirements . . . . . . . . . . . . . . . . . . 5
3.2. Requirements on Network Action Indicators . . . . . . . . 6
3.3. Requirements on Ancillary Data . . . . . . . . . . . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Working Group Adoption Comments . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
There is significant interest in developing the MPLS data plane to
address the requirements of new applications
[I-D.saad-mpls-miad-usecases]. These applications typically require
the inclusion of ancillary data in the MPLS packet. This data may be
encoded either in the label stack or below the bottom of the label
stack. This data is then either intercepted and processed, or some
other forwarding decision is taken by routers processing the packet.
The ancillary data is added by the ingress LSR, and is then processed
using mechanisms implemented by intermediate and/or egress LSRs that
comply with the MPLS base architecture and potentially its
extensions, including (but not limited to) [RFC3031], [RFC3032],
[RFC6790].
This draft specifies requirements for indicators in the MPLS label
stack to support these applications, as well as the encoding and use
of the ancillary data.
1.1. Terminology
o Ancillary Data (AD): Data relating to the MPLS packet that may be
used to affect the forwarding or other processing of that packet,
either at an Label Edge Router (LER) [RFC4221] or Label Switching
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Router (LSR). This data may be encoded within a network action
sub-stack (see below) (in-stack data), and/or after the bottom of
the label stack (post-stack data).
o Network Action: An operation to be performed on a packet. A
network action may affect router state, packet forwarding, or it
may affect the packet in some other way.
A network action is said to be present if there is an indicator in
the packet that invokes the action.
o Network Action Indication (NAI): An indication in the packet that
a certain network action is to be perfomed. There may be
associated ancillary data in the packet.
o Network Action Sub-Stack (NAS): A set of related, contiguous Label
Stack Entries (LSEs).
The first LSE contains the NAI. The TC and TTL values in the sub-
stack may be redefined.
The label field in the second and following LSE may be redefined.
Solutions MUST NOT redefine the S bit. See Section 3.1 through
Section 3.5.
o In-Stack Data: Any data within the MPLS label stack including the
outer LSE and the bottom of stack (the LSE with the S-bit set).
o Post-Stack Data: Any data beyond the LSE with the S-Bit set, but
before the first octet of the user payload. This document does
not prescribe whether post-stack data precedes or follows any
other protocol structure such as a control word or associated
channel header (ACH).
o Scope: The set of nodes that should perform a given action.
1.2. Background
The MPLS architecture is specified in [RFC3031] and provides a
mechanism for forwarding packets through a network without requiring
any analysis of the packet payload's network layer header by
intermediate nodes (Label Switching Routers - LSRs). Formally,
inspection may only occur at network ingress (the Label edge router -
LER) where the packet is assigned to a forwarding equivalence class
(FEC).
MPLS uses switching based on a label pushed on the packet to achieve
efficient forwarding and traffic engineering of flows associated with
the FEC. While originally used for IP traffic, MPLS has been
extended to support point-to-point, point-to-multipoint and
multipoint-to-multipoint layer 2 and layer 3 services. An overview
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of the development of MPLS is provided in
[I-D.bryant-mpls-dev-primer].
A number of applications have emerged which require LSRs to make
forwarding or other processing decisions based on inspection of the
network layer header, or some other ancillary information in the
protocol stack encapsulated deeper in the packet. An early example
of this was generation of a hash of the payload header to be used for
load balancing over Equal Cost Multipath (ECMP) or Link Aggregation
Group (LAG) next hops. This is based on an assumption that the
network layer protocol is IP. MPLS was extended to avoid the need
for LSRs to perform this operation if load balancing was needed based
on the payload and instead use only the MPLS label stack, using the
Entropy Label / Entropy Label Indicator [RFC6790] which are inserted
at the LER. Other applications where the intermediate LSRs may need
to inspect and process a packet on an LSP include OAM, which can make
use of mechanisms such the Router Alert Label [RFC3032] or the
Generic Associated Channel Label (GAL) [RFC5586] to indicate that an
intercepted packet should be processed locally. See
[I-D.bryant-mpls-dev-primer] for detailed list of such applications.
There have been a number of new proposals for how ancillary data is
carried in MPLS and how its presence is indicated to the LSR or
egress LER, for example In-situ OAM and Service Function Chaining
(SFC). A summary of these proposals is contained in
[I-D.bryant-mpls-dev-primer], an overview of use cases is provided in
[I-D.saad-mpls-miad-usecases]. [I-D.song-mpls-extension-header]
summarises some of the issues with existing solutions to address
these new applications (note that this document draws on the
requirements and issues without endorsing a specific solution from
[I-D.song-mpls-extension-header]):
These solutions rely on either the built-in next-protocol
indicator in the header or the knowledge of the format and size of
the header to access the following packet data. The node is
required to be able to parse the new header, which is unrealistic
in an incremental deployment environment.
A piecemeal solution often assumes the new header is the only
extra header and its location in the packet is fixed by default.
It is impossible or difficult to support multiple new headers in
one packet due to the conflicted assumption. An example of this
is that the GAL/G-ACH mechanism assumes that if the GAL is
present, only a single G-ACH header follows.
New applications therefore require the definition of extensions to
the MPLS architecture and label stack operations that can be used
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across these applications in order to minimise implementation
complexity and promote interoperability and extensibility.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. MPLS Network Action Indicator Requirements
This document specifies requirements of MPLS Network Action
Indicators, and the associated Ancillary Data. The requirements are
for the behavior of the protocol mechanisms and procedures that
constitute building blocks out of which indicators for network
actions and associated ancillary data are constructed.
It does not specify the detailed actions and processing that may be
required by an application for any ancillary data by an LSR or LER.
The requirements in this document do not describe what functions an
implementation must support. The purpose of this document is to
identify the toolkit and any new protocol work that is required.
This new protocol work MUST be based on the existing MPLS
architecture.
3.1. General Requirements
1. MPLS combines extensibility, flexibility and efficiency by using
control plane context combined with a simple data plane mechanism
to allow the network to make forwarding decisions about a packet.
Any solution MUST maintain these properties of MPLS.
2. Any solutions to these requirements MUST NOT restrict the
generality of MPLS architecture [RFC3031], [RFC3032].
3. If extensions to the MPLS data plane are required, they MUST NOT
be inconsistent with the MPLS architecture [RFC3031], [RFC3032].
4. Solutions meeting the requirements set out in this document MUST
be able to coexist with and MUST NOT obsolete existing MPLS
mechanisms.
5. The design of any mechanism SHOULD be such that an LSR is able to
efficiently parse the label stack.
6. Mechanisms MUST NOT increase the size of the MPLS label stack
more than is necessary.
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7. The design of solutions MUST NOT expose confidential information
[RFC6973] [RFC3552] to the LSRs.
8. Solution specifications MUST document any changes to the existing
MPLS data plane security model that they introduce.
3.2. Requirements on Network Action Indicators
1. When an MPLS Network Action is required, and indicator is
REQUIRED in the label stack.
2. An MPLS Network Action MUST specify whether ancillary data is
required in the label stack and/or post-stack data.
3. Any solution MUST respect the principle that Special Purpose
Labels are the mechanism of last resort and therefore must
minimise the number of new SPLs that are allocated.
4. Insertion, parsing, processing and disposition of Network Action
Indicators SHOULD make use of existing MPLS data plane
operations.
5. An NAI MUST NOT be delivered to a node that is not capable of
processing in the way in a way that is acceptable to the
imposing LER.
6. NAI MUST NOT become top of stack at a node that does not
understand how to perform a disposition operation on it.
Disposition includes both processing and ignoring.
7. The NAI design MUST support scoping of network actions.
8. A given NAI specification MUST specify if the scope is end-to-
end, hop-by-hop, or directed at one or more selected nodes.
9. If a design allows more than one scope, a mechanism MUST be
provided to specify the precedence of the scopes.
10. A mechanism is REQUIRED to enable an LER inserting NAIs to
determine if the far-end LER can accept and process a packet
containing a given NAI.
11. NAIs SHOULD be supported for both P2P and P2MP paths, but any
specific NAI may only be supported for one or the other.
12. Data plane mechanisms for NAIs MUST be consistent across
different control plane protocol types.
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13. A mechanism MUST be defined for control / management planes in
use to determine the ability of downstream LSRs/LERs to accept/
process a given NAI.
14. A mechanism is REQUIRED to enable an LSR to determine if an NAI
is present in a packet.
15. NAIs can only be inserted at LERs, but MAY be processed at LSRs
and LERs. If it is required to insert an NAI at a transit LSR
on an LSP, then a new label stack MUST be pushed.
16. It SHOULD be possible to include indicators for multiple network
actions in the same packet.
17. The solution MUST allow NAI-carrying and non-NAI-carrying
packets to coexist on the same LSP.
18. The solution MUST support the processing of a subset of the NAIs
on a packet.
19. Any specification of a solution that inserts or modifies the NAI
MUST discuss the possible ECMP consequences.
3.3. Requirements on Ancillary Data
1. Solutions for in-stack ancillary data MUST be able to coexist
with and MUST NOT obsolete existing MPLS mechanisms.
2. A common preamble for ancillary data MUST be defined so that a
node receiving the ancillary data can determine whether to
process, ignore, skip over or discard it according to network or
local policies.
3. Any specification of a mechanism MUST describe whether it can
coexist with existing post-stack data mechanisms e.g. control
words and G-ACH, and if so how this coexistence operates.
4. A mechanism MUST be defined for an LER inserting ancillary data
to determine that each node that needs to process the ancillary
data can read the required distance into the packet at that
node, for example [RFC9088].
5. Ancillary data MAY be associated with control or maintenance
information for traffic carried by an LSP, and/or it MAY be
associated with the user traffic itself.
6. For scoped ancillary data, a mechanism is REQUIRED to enable an
LER inserting NAIs whose network actions make use of that
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ancillary data, to determine if the NAI and ancillary data will
be processed by LSRs within the scope along the path. Such a
mechanism MAY need to determine if LSRs along the path can
process a specific type of AD implied by the NAI at the depth in
the stack that it will be presented to the LSR.
7. Network action specifications MUST specify if the ancillary data
needs to be processed as a part of the immediate forwarding
operation and whether packet mis-ordering is allowed to occur as
a result of the time taken to process the ancillary data.
8. In order to prevent unnecessary scanning of the packet, care
needs to be taken in the location of post stack ancillary data,
for example it SHOULD be located as close to the bottom of the
label stack as possible.
9. A solution MUST be provided to verify the authenticity of
ancillary data processed to LSRs [RFC3552].
10. The design of the ancillary data MUST NOT expose confidential
information [RFC6973] [RFC3552] to the LSRs.
4. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
5. Security Considerations
The mechanisms required by this document introduce new security
considerations to MPLS. Individual solution specifications meeting
these requirements MUST address any security considerations.
6. Acknowledgements
The authors gratefully acknowledge the contributions from Greg
Mirsky, Yingzhen Qu, Haoyu Song, Tarek Saad, Loa Andersson, Tony Li,
John Drake and Bruno Decraene.
The authors also gratefully acknowledge the input of the members of
the MPLS Open Design Team.
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7. References
7.1. 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>.
[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>.
7.2. Informative References
[I-D.bryant-mpls-dev-primer]
Bryant, S., "A Primer on the Development of MPLS", draft-
bryant-mpls-dev-primer-01 (work in progress), December
2021.
[I-D.saad-mpls-miad-usecases]
Saad, T., Makhijani, K., Song, H., and G. Mirsky, "Use
Cases for MPLS Network Action Indicators and MPLS
Ancillary Data", draft-saad-mpls-miad-usecases-02 (work in
progress), April 2022.
[]
Song, H., Li, Z., Zhou, T., Andersson, L., and Z. Zhang,
"MPLS Extension Header", draft-song-mpls-extension-
header-06 (work in progress), January 2022.
[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>.
[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>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/info/rfc3552>.
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[RFC4221] Nadeau, T., Srinivasan, C., and A. Farrel, "Multiprotocol
Label Switching (MPLS) Management Overview", RFC 4221,
DOI 10.17487/RFC4221, November 2005,
<https://www.rfc-editor.org/info/rfc4221>.
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009,
<https://www.rfc-editor.org/info/rfc5586>.
[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>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>.
[RFC9088] Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
and M. Bocci, "Signaling Entropy Label Capability and
Entropy Readable Label Depth Using IS-IS", RFC 9088,
DOI 10.17487/RFC9088, August 2021,
<https://www.rfc-editor.org/info/rfc9088>.
Appendix A. Working Group Adoption Comments
1. Normative Language
Use of the normative language, Terminology section in
particular. For example, in "There may be associated ancillary
data in the packet."
2. The NAS abbreviation
Network Action Sub-Stack is abbreviated as NAS. I think that
abbreviating as NASS or presenting the extended term as Network
Action Sub-stack improves correlation between the full form and
acronym.
3. non-use of NAS abbreviation
Also, I've noticed that NAS is not used throughout the document.
It might not be useful after all.
4. Section 3.2 typo
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Perhaps a typo in the first requirement Section 3.2 s/and/an/ It
is not clear what "NAI is delivered to a node" might mean in the
requirement 5 of Section 3.2. Perhaps the next requirement is
sufficient and #5 can be removed from the document.
5. Extra words
Also, #5 seems like it has some extra wording. Perhaps s/in the
way in a way/in a way/?
6. Merging of drafts?
One thing I'm debating is whether draft-bryant-mpls-dev-
primer-01 - A Primer on the Development of MPLS (ietf.org)
should be merged with this draft?
7. ADI -> NAI
In this version the term "Ancillary Data Indicator" is changed
to "Network Action Indicator". While there is some difference
between the definition of the two terms: Ancillary Data
Indicator (ADI): A indicator in the MPLS label stack that
ancillary data exists in this packet. It MAY also indicate the
specific type of the ancillary data. Network Action Indication
(NAI): An indication in the packet that a certain network action
is to be performed. There may be associated ancillary data in
the packet. The above definition shows that ADI firstly is the
indicator of the existence of the ancillary data, and optionally
can be the indicator of specific type of ancillary data. While
NAI is only the indicator of a certain type of network action.
Thus NAI cannot replace ADI directly in this document. I'd
suggest to add the ADI back to the terminology section, and
change all the NAI in section 3.2 back to ADI. If needed, the
requirements on NAI can be added as separate items.
8. Addition to section 3.1
For backward compatibility and consistency, It is suggested to
add the below items to section 3.1 as general requirements: a)
Solutions meeting the requirements set out in this document MUST
be compatible with existing MPLS mechanisms. b) Solutions
meeting the requirements set out in this document MUST reuse
existing MPLS mechanisms when possible. c) For network actions
which are developed or under development in IETF, the encoding
and processing of the network action data MUST be reused.
9. Action Indicators without AD
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Do not use the ADI for Network Actions that does not have
ancillary data, use NADI (non-ADI).
10. AD definition
I was under the impression reading Jie's note that actions
_itself_ are the Ancillary Data. Your definition of "Ancillary
Data" seems to be limited to action parameters or metadata which
is likely why you draw such conclusions.
11. Optional AD?
AD definition treats anything new to the current label stack as
an optional add-on == ancillary while NAI treats only optional
parameters or metadata associated with newly defined actions as
ancillary.
12. ADI and NAI are different
It is also my understanding that the definition of ADI and NAI
are different. ADI is used to indicate that there is
information in addition to the legacy label stack in the packet,
while NAI is used to indicate a certain type of network action.
The existence of NAI and the optional data associated with the
action need an indicator, which is the ADI.
13. Retire ADI
There is no need for an ancillary data indicator and we should
probably retire the term.
14. AD generic?
As Robert and I mentioned, the term ancillary data is generic
and refers to all types network actions information, including
those with and without additional action data.
Thus NAI can be considered as one type of ancillary data.
15. What ADI indicates
An ADI is the indicator of the presence of ANY non-label
information in the MPLS packet. Following it there may be
indicators of each specific network action. And my
understanding is the requirements in section 3.2 was mainly on
the ADI.
16. Common requirement to carry AD
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According to the use cases collected, their common requirement
is to carry ancillary data in the data packet to affect the
packet forwarding or processing behavior, or the network states.
There is no specific requirement on where the ancillary data
should be put in the packet. Thus in the requirement document
it would be clear enough to just mention ancillary data and its
indicator (ADI).
17. Not discussed
We have not discussed changing ADI to NAI.
18. Discussed when draft presented in the Open DT
The change of ADI to NAI was presented when the new version of
the Framework were discussed in the Open DT.
19. Comment from Loa
I think both comment 17 and 18, could be misunderstod, yes the
NAI was introduced (for good reason) in new Framework, however
it does not in itself exclude have an ADI in a packet, only that
is not the all-emcompassing term that it was earlier.
20. Keep using ADI
My suggestions would be to keep using ADI for the generic
indicator, and could use NAI for the indicator of specific
action. I don'think we need to mention NAS here, which is
specific to ISD based solution.
21. Use of NSI
I propose Network Action Sub-stack Indcator (NSI) for this
purpose.
Proposed definition: An LSE used to indicate the presence of a
Network Action Sub-stack.
22. Revise definition of NAS
We should also revise the definition of NAS to use this (21).
23. Popping NAS
When you pop a stack in programming, the concept that MPLS
borrowed, you pop the procedure indicator and the procedure
parameters. This is consistent with popping an NAS
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24. More than a name change
No it is more than just a name change. There is a concept
change and we re-wrote a bunch of text to align with the NAI
approach. For example an NAI may not have AD to indicate.
25. Writeable NAS
I have some further questions. NAS is something within the
label stack but writable by intermediate nodes. Is this the
stack operation? Besides, if NAS emerges at ToS, you said it'll
be popped and discarded. What if the NAS also needs to be
applied to the labels below it? Whatever measures you will take
here, are those the stack operations?
26. The NFRR use case
I have several questions about the NFRR use case. As I
understand it, a point of local repair (PLR) imposes NAS with
the NFRR indicator so that it becomes ToS at the merge node
(MN). If that is correct, then the MN will remove the NAS with
the NFRR indicator as the packet is returned on the "normal"
path. Hence, I don't see why an intermediate node would need to
write into an existing in the label stack NAS in support of
NFRR.
27. Intermediate node re-writing
I may not see a case for an intermediate node re-writing the
existing NAI. I think that the node should impose a new NAS. I
see the case for an intermediate node writing into PSD (e.g.,
HbH IOAM though I think that is too expensive and the IOAM
Direct Export or Hybrid Two-Step are a better choice). To
summarize, I don't see the need for an intermediate node to
write into ISD and am open to discussing the node writing into
PSD.
28. Two types of indicators
One of my concern is that there are two types of indicators, and
they cannot be represented using the same term. - The first one
(call it indicator-1) is used to indicate the presence of any
non-forwarding-label information in the packet. As discussed it
may be realized as a bSPL. It does not indicate the type of
actions to be performed. - The second type of indicator (call
it indicator-2) is used to indicate the presence of a specific
type of action. Such action may or may not have associated data
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with it. This may be realized as a Flag or an action type in
the packet.
29. Second term needed
do not understand why we need another term. We have not had a
situation where we wanted to refer to "NAS + PSD" and lacked a
term for it.
30. Propose text
That said, please feel free to propose a term and a definition.
I do not understand why we need another term. We have not had a
situation where we wanted to refer to "NAS + PSD" and lacked a
term for it.
That said, please feel free to propose a term and a definition.
31. NAS not general enough
Thus NAS is not general enough to cover the PSD. What we need
is a generic term to cover all the possible cases of ancillary
data. Furthermore, the indicator and the ancillary data would
need separate terms anyway and does not need to be coupled under
one term.
32. Use of ancillary data
* We are already using ancillary data for this purpose
* Exactly, and that' why we don't need to mention NAS in the
requirement document.
33. What the NAS contain
* Let me put it this way: By definition, NAS contains: ADI,
Optional NAI and Optional ISD. While what we want to refer
to with the term is: Optional NAI Optional ISD and Optional
PSD. Note it does not include the ADI.
* This is incorrect. It contains a network action sub-stack
indicator, network action indicators, and any in-stack
ancillary data (as defined by the specified network actions)
34. User-defined actions
user-defined network actions? Should we mentione in the
requirements doc?
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35. draft-ietf-mpls-mna-requirements
I hope, if adopted, the filename can be adjusted to use MRN not
MIAD-ADI.
Comment from Loa: I think the filename we are considering is:
draft-ietf-mpls-mna-requirements
36. In the Abstract (1)
This work is the product of the IETF MPLS Open Design Team.
Before posting as a Working Group draft, this sentence needs to
be removed. It's OK to say something in the Acknowledgements.
Loa: Depending on what is meant by "before", I have a comment on
this, just because info is at the wrong place it should not be
considered "blocking" and could be update at any time.
Personally I think working group draft version -01 would be a
good place to do this update.
37. In the Abstract (2)
The term "application data" may be (is) confusing. While you
probably mean it to imply an application of MPLS, it may be
confused with the type of application that runs end-to-end
(i.e., on a host). Although, reading some of the text, it does
feel like some of the time you _are_ intending to imply that the
application software may somehow be able to provide the
ancillary data that is ultimately carried by MPLS.
I think, in the Abstract, you could say...
based on ancillary data that may be carried in or below the
bottom of the label stack.
...but you should probably look through the rest of the text and
consider the use of the word "application." Maybe one approach
would be to specifically call out the term near the top of the
document in order to correctly set the context.
38. In section 1 (1).
is then processed using mechanisms implemented by intermediate
and/or egress LSRs that comply with the MPLS base architecture
and potentially its extensions, including (but not limited to)
[RFC3031], [RFC3032],[RFC6790].
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This sounds like the mechanisms to process the ancillary data
are already specified in those RFCs, but (of course) that's not
the case.
You are probably making a point about the nodes being "MPLS" and
also saying something about backward compatibility of the
mechanism. But it should be clear that only nodes that contain
new functionality will be able to recognise and process
ancillary data.
39. In section 1 (2).
This draft specifies
Say 'document' so that you are future-proofed for publication as
an RFC.
40. In section 1.1 (1)
s/an Label/a Label/ s/perfomed/performed/
41. In section 1.1 (2).
* Network Action: An operation to be performed on a packet. A
network action may affect router state, packet forwarding, or
it may affect the packet in some other way.
If the operation affects router state, is it really performed on
the packet?
42. In section 1.1 (3)
* Network Action Indication (NAI): An indication in the packet
that a certain network action is to be perfomed. There may
be associated ancillary data in the packet
* Network Action Sub-Stack (NAS): A set of related, contiguous
Label Stack Entries (LSEs). The first LSE contains the NAI.
The TC and TTL values in the sub-stack may be redefined.
The first bullet simply says that the NAI is "in the packet",
but the second bullet goes on to define where/how it is carried.
I would say that it is totally irrelevant to the _requirements_
how the NAI is encoded/carried (although there may be some
requirements that limit the options). But I note that there is
no further mention of the NAS or of a "sub-stack". I suggest
removing this second bullet.
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43. In section 1.1 (4)
* In-Stack Data: Any data within the MPLS label stack including
the outer LSE and the bottom of stack (the LSE with the S-bit
set).
* Post-Stack Data: Any data beyond the LSE with the S-Bit set,
but before the first octet of the user payload. This
document does not prescribe whether post-stack data precedes
or follows any other protocol structure such as a control
word or associated channel header (ACH).
Does "any data" mean "any ancillary data"?
44. In section 1.2 (1)
s/number of new proposals/number of proposals/
45. In Section 1.2 (2)
for example In-situ OAM and Service Function Chaining (SFC)
Might benefit from references for iOAM and SFC.
46. In section 1.2 (3)
[] summarises some of the issues
with existing solutions to address these new applications (note
that this document draws on the requirements and issues without
endorsing a specific solution from
[I-D.song-mpls-extension-header]):
This gives more emphasis to the referenced draft than I think
you intend. If you intend that people read that draft to see
the issues, it is a normative reference. But if you are just
mentioning it and have pulled the information into this
document, then you need to reduce the emphasis. How about...
[] sets out some of the issues in
how existing solutions address these new applications. This
document draws on the requirements and issues noted in that
document without endorsing any specific solution.
47. Section 2
While I understand the desire to express the requirements in
definitive language, BCP14 is not about requirements. Rather it
is intended to describe implementation behaviours.
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A way around this that is often used is to include a subsequent
paragraph such as...
Although this document is not a protocol specification, this
convention is adopted for clarity of description of
requirements.
See, for example, RFC 4139, RFC 4687, or RFC 5862.
48. In section 3.2 (1)
s/and indicator/an indicator/
49. In section 3.2 (2)
(2). An MPLS Network Action MUST specify whether ancillary data
is required in the label stack and/or post-stack data.
Do you mean this, or do you mean that this must be specified in
the documentation of the NA?
50. In section 3.2 (1)
(3). Any solution MUST respect the principle that Special
Purpose Labels are the mechanism of last resort and therefore
must minimise the number of new SPLs that are allocated.
Presumably a minimum here would be zero?
Loa: No we have considere this and decided that there is room to
specify 1 bSPL for MNA.
Loa: I also think that we should s/Special Purpose Labels/Base
Special-Purpose Labels Note: for the Extended SPLs there sare no
such reestriction.
51. In section 3.2 bullet 5
s/in the way in a way/in a way/
52. In section 3.2 (bullet, 5, 6 and 10)
Bullet 10 is a wholly contained subset of bullet 5. Actually,
bullet 10 is a wholly contained subset of bullet 6. Makes me
think that bullets 5 and 6 possibly say the same thing as each
other.
53. In section 3.2 (2)
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(11). NAIs SHOULD be supported for both P2P and P2MP paths, but
any specific NAI may only be supported for one or the other.
Really? You can't have an NAI that is equally applicable for
both P2P and P2MP? Seems an odd restriction to impose.
54. In section 3.2 (3)
(15). NAIs can only be inserted at LERs, but MAY be processed
at LSRs and LERs. If it is required to insert an NAI at a
transit LSR on an LSP, then a new label stack MUST be pushed.
What does it mean to push a new label stack? If you mean that
we should support "MPLS in MPLS" encapsulation so that the
packet has two bottom of stack bits set, I should point out that
this was previously discussed and abandoned because the presence
of an LSE immediately after a set bottom of stack bit was
considered unacceptable because of the assumptions made by
existing hardware about what follows the bottom of stack.
55. In section 3.2 (4)
(19). Any specification of a solution that inserts or modifies
the NAI MUST discuss the possible ECMP consequences.
This seems to at least partially contradict 3.2/15
It is also not clear what it means "to modify an indication in
the packet that a certain network action is to be performed". I
guess it means to remove the NAI?
56. In section 3.3 (1)
(3.3/1) is surely already covered by 3.3/4
57. In section 3.3 (2)
(3.3/3) seems to be unnecessary given 3.3/1
58. Semantic Routing
I think the proposal here falls in the scope of "Semantic
Routing". That is, adding information to packets so that the
forwarding decisions may be enhanced to act not just on the
destination address or next hop label, but also on the
additional information. The precise forwarding action may be
known by the forwarders by definition (such as a protocol
specification), installed by a routing engine according to a
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routing algorithm acting on information exchanged by routing
protocols, or programmed into the forwarder from a management or
orchestration system.
We wrote an introduction to the idea of Semantic Routing draft-
farrel-irtf-introduction-to-semantic -routing which you can look
at if you want some context.
We also set out to examine the challenges and concerns
introduced by Semantic Routing in draft-king-irtf-challenges-in-
routing and I think it would be good if this work was calibrated
against those challenges.
Loa: While semantic routing is intresting, and good be
"calibrated" against MNA as a whole (guiding documents and
solutions), I think it is out of scope for the requirement
document.
59. Understanding of Use Cases
I would think that a more detailed an understanding of the use
cases is needed before moving ahead with the requirements. I
wouldn't go as far as saying that the use cases need to be
referenced normatively, but I do think they need a little more
attention from the WG to motivate actually adopting this work.
That is, this document shows what we might need to do, but
without the use cases, we would be doing it "because we can" and
"because it might be useful one day." Those are not, I think
really good reasons to make fairly substantial changes to
deployed forwarding paradigms.
This is not to say that I dispute that there may be some
valuable use cases, but that the WG needs to agree which ones
are important in order to be sure that the requirements are on
target.
60. Conflicting text in document
I'm puzzled that some of the text in this document appears to
limit itself to cases that require ancillary data, while other
parts also consider the requirements for network functions that
don't require ancillary data, but do still need to be encoded in
the label stack in some way. I suspect this is just editorial,
but while the document title is "Requirements for MPLS Network
Action Indicators and MPLS Ancillary Data" the Abstract says
"This draft specifies requirements for indicators in the MPLS
label stack to support ancillary data in the packet and high
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level requirements on that ancillary data," and the Introduction
seems entirely focused on the ancillary data case.
It would be good to be clear, at the point of adoption, which
way we are jumping on this question.
draft-andersson-mpls-mna-fwk
seems to be fully behind network actions some of which may also
require ancillary data.
Perhaps this document should reference that one for additional
information?
61. Loa: I have been thinking about a short text (1 or 2 paragraphs)
on how the guiding documents fit togehter that should appear,
e.g. in the introduction of all 3 documents. It could be added
later in the process, but should be there when the documents go
to wglc. Let me know if there are someone that will help work
on this,
Authors' Addresses
Matthew Bocci
Nokia
Email: matthew.bocci@nokia.com
Stewart Bryant
University of Surrey 5GIC
Email: sb@stewartbryant.com
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