Internet DRAFT - draft-jags-mpls-mna-hdr
draft-jags-mpls-mna-hdr
MPLS Working Group J. Rajamanickam, Ed.
Internet-Draft R. Gandhi, Ed.
Intended status: Standards Track Cisco Systems, Inc.
Expires: 14 July 2023 R. Zigler, Ed.
Broadcom
H. Song, Ed.
Futurewei Technologies
K. Kompella, Ed.
Juniper Networks
10 January 2023
MPLS Network Action (MNA) Sub-Stack Solution
draft-jags-mpls-mna-hdr-05
Abstract
This document defines the MPLS Network Action (MNA) sub-stack
solution for carrying Network Actions and Ancillary Data in the label
stack. MPLS Network Actions can be used to influence packet
forwarding decisions, carry additional OAM information in the MPLS
packet, or perform user-defined operations. This document addresses
the MNA requirements specified in draft-ietf-mpls-mna-requirements.
This document follows the MNA framework specified in draft-ietf-mpls-
mna-fwk.
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
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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
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This Internet-Draft will expire on 14 July 2023.
Copyright Notice
Copyright (c) 2023 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
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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
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Label Stack Entry Formats . . . . . . . . . . . . . . . . . . 5
4.1. LSE Format A: The MNA Sub-Stack Indicator . . . . . . . . 5
4.2. LSE Format B: The initial opcode . . . . . . . . . . . . 6
4.3. LSE Format C: Subsequent opcodes . . . . . . . . . . . . 6
4.4. LSE Format D: Additional Data . . . . . . . . . . . . . . 7
5. The MNA Sub-Stack . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Data . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.4. Unknown Action Handling . . . . . . . . . . . . . . . . . 9
5.5. Ordering . . . . . . . . . . . . . . . . . . . . . . . . 10
5.6. Examples . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Special Opcodes . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. bSPL Protection . . . . . . . . . . . . . . . . . . . . . 11
6.2. PSD Offset . . . . . . . . . . . . . . . . . . . . . . . 11
6.3. Flag-Based NAIs without AD . . . . . . . . . . . . . . . 12
6.4. Flag based NAIs with AD . . . . . . . . . . . . . . . . . 12
6.5. PSD-ISD Ordering . . . . . . . . . . . . . . . . . . . . 13
6.6. Extension Opcode . . . . . . . . . . . . . . . . . . . . 13
7. NAS placement in the Label Stack . . . . . . . . . . . . . . 13
8. Node Capability Signaling . . . . . . . . . . . . . . . . . . 14
9. Processing the Network Action Sub-Stack . . . . . . . . . . . 14
9.1. Encapsulating Node Responsibilities . . . . . . . . . . . 14
9.2. Transit Node Responsibilities . . . . . . . . . . . . . . 15
9.3. Penultimate Node Responsibilities . . . . . . . . . . . . 15
9.4. Decapsulating Node Responsibilities . . . . . . . . . . . 15
10. Network Action Indicator Allocation Procedures . . . . . . . 15
11. Backward Compatibility . . . . . . . . . . . . . . . . . . . 16
12. Security Considerations . . . . . . . . . . . . . . . . . . . 17
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
13.1. MNA bSPL Label . . . . . . . . . . . . . . . . . . . . . 17
13.2. MPLS Network Actions Parameters . . . . . . . . . . . . 18
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13.3. Network Action Flags With Ancillary Data . . . . . . . . 18
13.4. Network Action Flags Without Ancillary Data . . . . . . 18
13.5. Network Action Opcodes . . . . . . . . . . . . . . . . . 19
14. Appendix A: Examples . . . . . . . . . . . . . . . . . . . . 20
14.1. Network Action Encoding Examples . . . . . . . . . . . . 20
14.1.1. Network Action Flags without AD . . . . . . . . . . 20
14.1.2. Network Action Opcode with AD . . . . . . . . . . . 21
14.1.3. Network Action Opcode with more AD . . . . . . . . . 22
14.2. Post-Stack Network Action Encoding . . . . . . . . . . . 22
14.2.1. NAS that only indicates Post-Stack NAs . . . . . . . 23
14.2.2. NAS with both in-stack and post-stack NAs . . . . . 23
14.2.3. NASes with multiple scopes . . . . . . . . . . . . . 24
14.3. Network Action Processing Order . . . . . . . . . . . . 24
14.3.1. Network Action Processing Order . . . . . . . . . . 24
14.3.2. Post-Stack NA Processing Order . . . . . . . . . . . 25
14.3.3. A mix of in-stack and post-stack NAs . . . . . . . . 26
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
15.1. Normative References . . . . . . . . . . . . . . . . . . 26
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 28
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction
[RFC3032] defines the encoding of the MPLS label stack, the basic
structure used to define a forwarding path. Forthcoming applications
require MPLS packets to perform special network actions and carry
optional Ancillary Data (AD) that can affect the packet forwarding
decision or trigger OAM logging, for example. Ancillary Data can be
used to carry additional information, such as a network slice
identifier or an entropy value for load balancing. Several MNA
applications are described in [I-D.ietf-mpls-mna-usecases]. User-
defined network actions allow new, local actions to be defined.
This document defines the syntax and semantics of network actions
encoded within an MPLS Label Stack. Network actions can be encoded
with or without Ancillary Data (AD), either in or after the 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) (value TBA). This document addresses
the requirements specified in [I-D.ietf-mpls-mna-requirements]. This
document follows the framework specified in [I-D.ietf-mpls-mna-fwk].
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 [RFC2119] [RFC8174]
when, and only when, they appear in all capitals, as shown here.
2.2. Abbreviations
The terminology defined in [I-D.ietf-mpls-mna-fwk] and
[I-D.ietf-mpls-mna-requirements] are used in this document.
+============+===================+==================================+
|Abbreviation|Meaning | Reference |
+============+===================+==================================+
|AD |Ancillary Data | [I-D.ietf-mpls-mna-requirements] |
+------------+-------------------+----------------------------------+
|bSPL |Base Special | [RFC9017] |
| |Purpose Label | |
+------------+-------------------+----------------------------------+
|BOS |Bottom Of Stack | [RFC3032] |
+------------+-------------------+----------------------------------+
|HBH |Hop-By-Hop Scope | [I-D.ietf-mpls-mna-fwk] |
+------------+-------------------+----------------------------------+
|I2E |Ingress-To-Egress | [I-D.ietf-mpls-mna-fwk] |
| |Scope | |
+------------+-------------------+----------------------------------+
|IHS |I2E, HBH, or | This document |
| |Select Scope | |
+------------+-------------------+----------------------------------+
|ISD |In-Stack Data | [I-D.ietf-mpls-mna-requirements] |
+------------+-------------------+----------------------------------+
|LSE |Label Stack Entry | [RFC3032] |
+------------+-------------------+----------------------------------+
|MNA |MPLS Network | [I-D.ietf-mpls-mna-fwk] |
| |Actions | |
+------------+-------------------+----------------------------------+
|NAI |Network Action | [I-D.ietf-mpls-mna-requirements] |
| |Indicator | |
+------------+-------------------+----------------------------------+
|NAL |Network Action | This document |
| |Length | |
+------------+-------------------+----------------------------------+
|NAS |Network Action | [I-D.ietf-mpls-mna-fwk] |
| |Sub-Stack | |
+------------+-------------------+----------------------------------+
|NASI |Network Action | This document |
| |Sub-Stack | |
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| |Indicator | |
+------------+-------------------+----------------------------------+
|NASL |Network Action | This document |
| |Sub-Stack Length | |
+------------+-------------------+----------------------------------+
|OAM |Operations And | [RFC4377] |
| |Management | |
+------------+-------------------+----------------------------------+
|P |Post-Stack Network | This document |
| |Action Presence | |
| |Indicator | |
+------------+-------------------+----------------------------------+
|PSD |Post-stack data | [I-D.ietf-mpls-mna-requirements] |
| | | and [I-D.ietf-mpls-mna-fwk] |
+------------+-------------------+----------------------------------+
|TC |Traffic Class | [RFC5462] |
+------------+-------------------+----------------------------------+
|TTL |Time To Live | [RFC3032] |
+------------+-------------------+----------------------------------+
Table 1: Abbreviations
3. Overview
The MPLS Network Action Sub-Stack (NAS) 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 encapsulated packet. Multiple NASes may appear in a
label stack and the packet may contain Post-Stack Data, including
additional network actions, as specified in
[I-D.song-mpls-extension-header].
Network actions and their optional Ancillary Data (AD) may be encoded
as part of the NAS as a series of LSEs.
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 a traditional LSE, as described in [RFC3032] and
[RFC5462].
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
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.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode | Data |P|IHS|S| Res |U| NASL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2
* Opcode (7 bits) : The operation code for this LSE. See
Section 5.1.
* Data (13 bits) : Opcode specific data
* P (1 bit) : If set, it indicates the presence of post-stack
network actions.
* IHS (2 bits) : The scope of the sub-stack. See Section 5.3.
* S (1 bit) : The Bottom of Stack [RFC3032].
* Res (3 bits) : Reserved bits. These must be transmitted as zero
and ignored upon receipt.
* U (1 bits): Unknown Action Handling. See Section 5.4.
* NASL (4 bits) : The Network Action Sub-Stack Length (NASL). The
number of additional LSEs in the sub-stack, not including the
leading Format A LSE and the Format B LSE.
4.3. LSE Format C: Subsequent opcodes
LSE Format C is used to encode the subsequent opcodes in the NAS.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode | Data |S| Data | NAL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 3
* Opcode (7 bits) : The operation code for this LSE. See
Section 5.1.
* Data (16 bits + 4 bits) : Opcode specific data
* S (1 bit) : The Bottom of Stack [RFC3032].
* NAL (4 bits): Network Action Length. The number of LSEs of
additional data, encoded in LSE Format D (Section 4.4) following
this LSE.
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 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Data |S| Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4
* 1 (1 bit) : The most significant bit MUST be set. This prevents
legacy implementations from misinterpreting this LSE as containing
a special label.
* S (1 bit) : The Bottom of Stack [RFC3032].
* Data (22 bits + 8 bits) : Opcode specific data
5. The MNA Sub-Stack
The MNA Sub-Stack MUST begin with a Format A LSE (Section 4.1). The
label field of the LSE contains the MNA bSPL (value TBA) to indicate
the presence of the MNA Sub-Stack.
The TC and TTL fields of the first LSE retain their traditional
semantics, as the penultimate node on the path may copy the TTL and
TC fields from the preceding LSE to the next LSE on the label stack,
overwriting the TTL and TC fields of the next LSE, as specified in
Section 3.5 of [RFC3443]. If the node performing this copy is not
aware of MNA, this could overwrite the values in the first LSE of the
MNA sub-stack.
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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.
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 field. All
Format D LSEs MUST follow a Format C LSE and be included in that
LSE's NAL field.
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 allocated through IANA
(Section 10 and Section 13.5).
5.2. Data
The data field carries opcode specific data. This may be ancillary
data for a network action.
To preserve backward compatibility, if a network action encodes data
that will change during packet forwarding, then that data MUST be in
the least significant 4 bits in the data field of a Format C LSE
(Section 4.3) or the least significant 8 bits of a Format D LSE
(Section 4.4). Some legacy implementations may use the label field
in all LSEs when computing ECMP decisions and modifying the label
field might disrupt that packet's flow.
5.3. Scope
The IHS field in the Format B LSE indicates the scope of the In-Stack
and Post-Stack 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:
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+======+==========+
| Bits | Scope |
+======+==========+
| 00 | I2E |
+------+----------+
| 01 | HBH |
+------+----------+
| 10 | Select |
+------+----------+
| 11 | Reserved |
+------+----------+
Table 2: IHS Scope Values
Hop-By-Hop (HBH) - All nodes along the path MUST process the NAS.
Select - Only specific nodes along the path will perform the
action.
Ingress To Egress (I2E) - The NAS MUST be processed only by the
egress node.
A single NAS carries only one of the three scopes (HBH/Select/I2E).
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.
An I2E scope NAS 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.
Forwarding and egress nodes should process at most a single NAS per
scope. If a node is to process multiple NASes, it should process
them in the order that they appear in the label stack.
5.4. Unknown Action Handling
The Unknown Action Handling (U) field in a Format B 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 Action Handling actions are defined below.
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+=====+=====================+
| Bit | Action |
+=====+=====================+
| 0 | Skip to the next NA |
+-----+---------------------+
| 1 | Drop the packet |
+-----+---------------------+
Table 3: Unknown Action
Handling
5.5. Ordering
The network actions encoded in the NAS MUST be processed as if they
were processed in the order that they appear in the NAS, from the top
of the NAS to the bottom. NAI encoded as flags MUST be processed as
if they were processed from the most significant bit to the least
significant bit.
5.6. Examples
A minimal NAS would have the following format, where the Label field
would contain the MNA bSPL and the NASL value would be 0:
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode | Data |P|IHS|S| Res |U| NASL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5
A more complex NAS might have multiple opcodes and additional
Ancillary Data. This example has two opcodes and two additional LSEs
of AD.
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode | Data |P|IHS|S| Res |U| NASL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode | Data |S| Data | NAL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Data |S| Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Data |S| Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6
In this example, the NASL field would have value 3 and the NAL field
would have value 2.
6. Special Opcodes
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 is not used.
6.2. PSD Offset
Opcode: 1
Purpose: This opcode carries the start offset of the Post-Stack
Action Header (PAH) ([I-D.song-mpls-extension-header] ) within the
PSD.
LSE Format: B
Data: The data value of the LSE contains the offset from the MPLS BOS
in units of 4 octets. This allows the Generic Control Word (0000b)
[RFC4385] and G-ACh (0001b) [RFC5586] fields to be placed immediately
after the BOS. In the absence of this opcode, the PSD is encoded
immediately after the MPLS BOS. A data value of 1 indicates that the
PAH starts 4 octets after the BOS.
Scope: This opcode can be used with any scope.
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6.3. Flag-Based NAIs without AD
Opcode: 2
Purpose: Network actions that do not require Ancillary Data do not
require an entire LSE. 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 there are sufficient NAI, then Format D LSEs may be used to
encode more flags for more network actions. Flags are allocated from
the "Network Action Flags Without Ancillary Data" registry
(Section 13.3). If flags need to be evaluated in a different order,
multiple LSEs using this opcode may be used to specify the requested
order. If this opcode is used with LSE Format B, then only 13 flags
may be carried.
Scope: This opcode can be used with any scope.
This opcode MAY be used with no flags set in the data field to
signify that no operation is to be performed. This can be used, for
example, if the first action to be performed cannot be encoded in a
Format B LSE.
6.4. Flag based NAIs with AD
Opcode: 3
Purpose: This opcode supports flag-based network actions that have
Ancillary Data.
LSE Formats: C, D
Data: A format C LSE carries the Network Action Indicators, which
should be evaluated from the most significant bit to the least
significant bit. Flags are allocated from the "Network Action Flags
With Ancillary Data" registry (Section 13.4). If flags need to be
evaluated in a different order, multiple LSEs using this opcode may
be used to specify the requested order. Format D LSEs are used to
encode the associated Ancillary Data, which appears in the same order
as the flags.
Scope: This opcode can be used with any scope.
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If a flag contained within this opcode is unknown and is skipped per
Section 5.4, then the length of its associated ancillary data will
also be unknown. Any subsequent flags within the opcode will not
have the correct associated ancillary data, so all subsequent flags
SHOULD be treated as unknown actions and also skipped.
6.5. PSD-ISD Ordering
Opcode: 4
Purpose: In cases where the ordering of network action is significant
and where some of the network actions reside in PSD, this opcode can
be used to insert PSD network actions into the order of execution.
The 'P' bit and 'O' bit MUST be set in the NAS's Format B LSE if this
opcode is used.
LSE Format: B, C, D
Data: The data field contains one or more 8-bit Next Header (NH)
indicators [I-D.song-mpls-extension-header]. When used with LSE
Format B, only one NH indicator is carried. Two indicators MAY be
carried in a Format C LSE, and if Format D LSEs are used, each may
carry up to three indicators. The indicators are the stored
concatenated in the most significant bits of the data field. If
multiple indicators are carried, the most significant NH indicator is
evaluated to the least significant. Indicators do not span LSEs. If
some indicator positions are not to be used, then the indicator
should be set to No Next Header (NONE).
Scope: This opcode can be used with any scope.
6.6. Extension Opcode
Opcode: 127
Purpose: This opcode is reserved to extend the current opcode range
beyond 127. Future use of this opcode is out of scope.
7. NAS placement in the Label Stack
Regardless of whether packets are being forwarded based on Segment
Routing [RFC8662], LDP [RFC5036], or RSVP-TE [RFC3209], the node
adding an NAS to the label stack will need to place a copy of the NAS
where it can be read by the relevant nodes. Each node along the path
will have a Maximum MPLS Stack Inspection depth, and if the NAS is to
be processed by a particular node, then the entire NAS must be placed
so that it is within this depth by the time the packet reaches the
node.
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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 processes the top copy of
the NAS. Transit, non-penultimate nodes that pop a forwarding label
and expose a copy of the NAS MUST remove it. The penultimate node
that pops the forwarding label that exposes the last copy of the NAS
MUST NOT remove it. Instead, it forwards the packet with the NAS at
the top of stack to the next node (e.g., the segment endpoint node).
The node that receives the NAS at the top of the label stack has to
remove it.
For a NAS with Select scope, it is processed by the node that brings
it to the top of stack and then the NAS is removed from the stack.
For I2E scope, only one copy of the NAS needs to be added at the
bottom of the stack.
8. Node Capability Signaling
The head-end node which is adding a NAS MUST make sure that the
egress node removes the NAS. The head-end node MUST make sure that
the NAS can be processed by the appropriate transit and egress nodes.
* Each participating node MUST signal the network actions that it
supports.
* Each participating node MUST signal its Maximum MPLS Stack
Inspection Depth. This will allow the head-end node to place a
copy of an NAS at the correct stack depth.
The above capability signaling will be added in appropriate
protocols. Signaling details are outside the scope of this document.
9. Processing the Network Action Sub-Stack
This section defines the specific responsibilities for nodes along a
MPLS path.
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
limitations learned from Section 8.
The encapsulating node MUST NOT add a NAS to the label stack if the
decapsulation node does not support MNA.
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If there is an existing label stack, the encapsulating node SHOULD
NOT change the first 20 bits of each LSE in the label stack to avoid
ECMP path change.
If the encapsulating node is also a transit node, then it MUST also
respect transit node responsibilities.
9.2. Transit Node Responsibilities
Transit nodes SHOULD NOT change the first 20 bits in the LSEs in the
label stack.
A transit node MAY change the Ancillary Data found in the least
significant 8 bits of an LSE.
Transit nodes MUST process the NASes in the label stack, respecting
Section 5.5.
A transit node MUST respect the Unknown Action Handling value encoded
in the NAS.
A node that removes the only NAS that has the P bit set MUST remove
all PSD.
9.3. Penultimate Node Responsibilities
In addition to the transit node responsibilities above, the
penultimate node MUST NOT remove the last copy of a 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. Decapsulating Node Responsibilities
The decapsulating node MUST remove any NAS it receives.
10. Network Action Indicator Allocation Procedures
This section discusses the procedures and requirements for a
allocating a new opcode or flag as a network action indicator (NAI)
for a network action. A request for an NAI MAY make requests from
any combination of the "Network Action Opcodes", "Network Action
Flags With Ancillary Data", or "Network Action Flags Without
Ancillary Data" registries.
A request for a new NAI MUST include the following information:
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* Scope: The request MUST specify at-least one scope (I2E, HBH,
Select) for the Network Action. The request MAY specify more than
one scope.
* Ancillary Data: A request MUST specify the quantity, syntax, and
semantics of any associated Ancillary Data. The Ancillary Data
MAY be variable length, but the length MUST be computable based on
the data present in the NAS.
* Processing: The request MUST specify the detailed procedure for
processing the network action.
A request for a new NAI MAY request any combination of flags or an
opcode. 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. If
ancillary data is required, then the optimal choice may depend on how
the action is likely to be combined with other actions. If the
action is unlikely to be used in combination with other actions and
at most 20 bits of ancillary data is required, then an opcode may be
preferred as the encoding will only consume a single LSE. If the
action is likely to be combined with other actions, then a flag is
more likely to be optimal.
11. Backward Compatibility
This section discusses interactions between MNA capable and legacy,
non-MNA capable 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 a non-MNA capable node. If such a packet did
arrive at a non-MNA capable node, it will most likely be dropped.
Legacy nodes may scan the label stack, potentially looking for a
label field 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).
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The TC and TTL fields 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 fields.
To protect against this, we retain the TC and TTL fields in the
Format A LSE.
12. Security Considerations
The security considerations in [RFC3032] 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, this 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 IETF needs to ensure that only secure
network actions are defined.
* 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 locally defined network
actions do not compromise the security of the network.
13. IANA Considerations
13.1. 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.
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13.2. 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)" registry group. The registries
described below should belong to this new registry group.
13.3. Network Action Flags With Ancillary Data
This document requests that IANA create a new registry with the name
"Network Action Flags With Ancillary Data". Registration requests
should comply with Section 10. The registration procedure for this
registry is "IETF Review". 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 C Data fields. Bit Position 0 is the most
significant bit a LSE Format C Data field. There are 20 bit
positions currently available, 0-19. This registry may be extended
in the future. Further opcodes would need to be defined to carry
additional flag ranges.
The initial assignments for this registry are:
+==============+=============+===============+
| Bit Position | Description | Reference |
+==============+=============+===============+
| 0-15 | Unassigned | |
+--------------+-------------+---------------+
| 16-19 | Private Use | This document |
+--------------+-------------+---------------+
Table 4: Network Action Flags With
Ancillary Data Registry
13.4. 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". 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 a LSE Format B or C
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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 available in LSE Format D. There are at most 15 Format D LSEs
per opcode, so there are at most 20 + 15 * 30 = 470 bit positions.
The Bit Position is an integer with value 0-469.
The initial assignments for this registry are:
+==============+=============+===============+
| Bit Position | Description | Reference |
+==============+=============+===============+
| 0-15 | Unassigned | |
+--------------+-------------+---------------+
| 16-19 | Private Use | This document |
+--------------+-------------+---------------+
| 20-469 | Unassigned | |
+--------------+-------------+---------------+
Table 5: Network Action Flags Without
Ancillary Data Registry
13.5. 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. The registration procedure for this registry is "IETF
Review". The fields are "Opcode" (integer), "Description" (string),
and "Reference" (string). Opcode is an integer 0-127.
The initial assignments for this registry are:
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+=========+=============================+===============+
| Opcode | Description | Reference |
+=========+=============================+===============+
| 0 | Reserved | This document |
+---------+-----------------------------+---------------+
| 1 | Offset of start of Post- | This document |
| | Stack Network Action Header | |
+---------+-----------------------------+---------------+
| 2 | Flag-Based Network Action | This document |
| | Indicators without AD | |
+---------+-----------------------------+---------------+
| 3 | Flag-Based Network Action | This document |
| | Indicators with AD | |
+---------+-----------------------------+---------------+
| 4 | PSD-ISD Ordering | This document |
+---------+-----------------------------+---------------+
| 5-110 | Unassigned | |
+---------+-----------------------------+---------------+
| 111-126 | Private Use | |
+---------+-----------------------------+---------------+
| 127 | Opcode Range Extension | This document |
| | Beyond 127 | |
+---------+-----------------------------+---------------+
Table 6: Network Action Opcodes Registry
14. Appendix A: Examples
14.1. Network Action Encoding Examples
14.1.1. Network Action Flags without AD
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label=MNA bSPL | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | Flags |P|IHS|S| Res |U| NASL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: NAS with Network Action Flags
This is an example of an NAS with Flag-Based NAIs without Ancillary
Data.
Details:
Opcode=2: This opcode to indicates that the LSE carries Flag-Based
NAIs without AD.
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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 field is set to "0", as there are no additional
LSEs.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label=MNA bSPL | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | Data=0 |P|IHS|S| Res |U| NASL=2|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | Flag-Based NAIs |0| NAIs | NAL=1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Additional Flag-Based NAIs |S|Flag-Based-NAIs|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Network Action Flags without AD using LSE Format D
In this example, the NAS contains a Format B LSE with no flags set,
indicating no operation. 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.
14.1.2. Network Action Opcode with AD
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-Label=bSPL (TBA) | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=8 | Ancillary Data |P|IHS|S| Res |U| NASL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Network action opcode with Ancillary Data
In this example, the NAS is carrying only one Network Action that
requires 13 bits of Ancillary Data.
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Details on the Second LSE
Opcode=8: A network action allocated outside of this document.
Data: The data field contains 13 bits of ancillary data.
14.1.3. Network Action Opcode with more AD
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 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label=MNA bSPL | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | Data=0 |P|IHS|0| Res |U| NASL=2|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=9 | Ancillary Data |0| AD | 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 allocated 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.
14.2. Post-Stack Network Action Encoding
The details of Post-Stack Network Action Extension Header encodings
are specified in [I-D.song-mpls-extension-header].
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14.2.1. NAS that only indicates Post-Stack NAs
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label=MNA bSPL | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | 0 |1|IHS|S| Res |U| NASL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |1| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Post-Stack Network Actions ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: NAS encoding only Post-Stack NAs
In some cases the NAS may encode only the presence of Post-Stack NAs.
In this case, the P-Bit is set. The IHS field indicates the scope of
the Post-Stack NAs (I2E, HBH, Select).
14.2.2. NAS with both in-stack and post-stack NAs
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label=MNA bSPL | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | 0 |1|IHS|0| Res |U| NASL=1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | Flag-Based NAIs |S| NAIs | NAL=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |1| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Post-Stack Network Actions Encoding ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 12: NAS with in-stack and post-stack NAs
In some cases the NAS may encode in-stack NAs and indicate the
presence of post-stack NAs. In this case, P-Bit is set. The NASL is
set to "1", indicating the presence of one additional LSE. The IHS
field indicates the scope of both the in-stack and post-stack NAs.
14.2.3. NASes with multiple scopes
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label=MNA bSPL | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | 0 |0| 1 |0| Res |U| NASL=1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | Flag-Based NAIs |0| NAIs | NAL=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label=MNA bSPL | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | 0 |1| 0 |1| Res |U| NASL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Post-Stack Network Actions Encoding ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: NASes with multiple scopes
In some cases the label stack may need to carry in-stack NAs with
Hop-By-Hop scope and post-stack NAs with I2E scope. In this case,
there will be two NASes in the label stack. In this case, the first
NAS will encode the in-stack NA with the Hop-By-Hop scope and the
second NAS will encode the presence of I2E scoped Post-Stack NAs.
14.3. 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.
14.3.1. Network Action Processing Order
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label=MNA bSPL | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=8 | Ancillary Data |P|IHS|S|Res|U|1| NASL=2|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=7 | Ancillary Data7 |S| AD7 | NAL=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | Flag-Based NAIs |S| NAI | NAL=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: 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 done by causing some NAIs to appear earlier
in the NAS.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label=MNA bSPL | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=8 | Ancillary Data |P|IHS|S|Res|U|1| NASL=3|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | 0x01 |S| NAI | NAL=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=7 | Ancillary Data7 |S| AD7 | NAL=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | 0x02 |S| NAI | NAL=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: Interleaving network actions
In the above example, opcode 8 is processed first, then Flag-Based
NAI 0x1 is processed before opcode 7, and finally NAI 0x2 is
processed.
14.3.2. Post-Stack NA Processing Order
By default, post-stack NAs follow the ordering specified in
[I-D.song-mpls-extension-header]. However, the PSD-ISD ordering
opcode can be used to override the default ordering and interleave
PSD actions with in-stack actions.
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14.3.3. A mix of in-stack and post-stack NAs
In some cases, post-stack NAs needs to be processed before in-stack
NAs. This section shows how to prioritize the post-stack NAs over
in-stack NAs.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label=MNA bSPL | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=8 | Ancillary Data |1|IHS|0| Res |U| NASL=3|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=2 | Flag-Based NAIs |0| NAIs | NAL=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=4 | Post-Stack NH 6 |0|PS-NAI | NAL=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode=7 | Ancillary Data |S| AD | NAL=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: Post-stack and in-stack NA processing order
In the above example, opcode 8 is processed first, then the Flag-
Based NAIs, followed by Post-Stack NH 6, and finally opcode 7.
15. References
15.1. Normative References
[I-D.ietf-mpls-mna-fwk]
Andersson, L., Bryant, S., Bocci, M., and T. Li, "MPLS
Network Actions Framework", Work in Progress, Internet-
Draft, draft-ietf-mpls-mna-fwk-02, 21 October 2022,
<https://www.ietf.org/archive/id/draft-ietf-mpls-mna-fwk-
02.txt>.
[I-D.ietf-mpls-mna-requirements]
Bocci, M., Bryant, S., and J. Drake, "Requirements for
MPLS Network Actions", Work in Progress, Internet-Draft,
draft-ietf-mpls-mna-requirements-04, 13 October 2022,
<https://www.ietf.org/archive/id/draft-ietf-mpls-mna-
requirements-04.txt>.
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[I-D.ietf-mpls-mna-usecases]
Saad, T., Makhijani, K., Song, H., and G. Mirsky, "Use
Cases for MPLS Network Action Indicators and MPLS
Ancillary Data", Work in Progress, Internet-Draft, draft-
ietf-mpls-mna-usecases-01, 24 October 2022,
<https://www.ietf.org/archive/id/draft-ietf-mpls-mna-
usecases-01.txt>.
[I-D.song-mpls-extension-header]
Song, H., Zhou, T., Andersson, L., Zhang, Z. J., and R.
Gandhi, "MPLS Network Actions using Post-Stack Extension
Headers", Work in Progress, Internet-Draft, draft-song-
mpls-extension-header-11, 15 October 2022,
<https://www.ietf.org/archive/id/draft-song-mpls-
extension-header-11.txt>.
[RFC2119] Bradner, S. and RFC Publisher, "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>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[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>.
[RFC4377] Nadeau, T., Morrow, M., Swallow, G., Allan, D., and S.
Matsushima, "Operations and Management (OAM) Requirements
for Multi-Protocol Label Switched (MPLS) Networks",
RFC 4377, DOI 10.17487/RFC4377, February 2006,
<https://www.rfc-editor.org/info/rfc4377>.
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
Use over an MPLS PSN", RFC 4385, DOI 10.17487/RFC4385,
February 2006, <https://www.rfc-editor.org/info/rfc4385>.
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[RFC5036] Andersson, L., Ed., Minei, I., Ed., Thomas, B., Ed., and
RFC Publisher, "LDP Specification", RFC 5036,
DOI 10.17487/RFC5036, October 2007,
<https://www.rfc-editor.org/info/rfc5036>.
[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>.
[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>.
[RFC8174] Leiba, B. and RFC Publisher, "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>.
[RFC8662] Kini, S., Kompella, K., Sivabalan, S., Litkowski, S.,
Shakir, R., and J. Tantsura, "Entropy Label for Source
Packet Routing in Networking (SPRING) Tunnels", RFC 8662,
DOI 10.17487/RFC8662, December 2019,
<https://www.rfc-editor.org/info/rfc8662>.
[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>.
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 and Greg Mirsky for reviewing our draft and providing many
useful suggestions.
Contributors
The following people have substantially contributed to this document:
Rajamanickam, et al. Expires 14 July 2023 [Page 28]
Internet-Draft MNA Sub-Stack January 2023
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
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
Rajamanickam, et al. Expires 14 July 2023 [Page 29]
Internet-Draft MNA Sub-Stack January 2023
Tony Li
Juniper Networks
United States
Email: tony.li@tony.li
John Drake
Juniper Networks
United States
Email: jdrake@juniper.net
Figure 17
Authors' Addresses
Jaganbabu Rajamanickam (editor)
Cisco Systems, Inc.
Canada
Email: jrajaman@cisco.com
Rakesh Gandhi (editor)
Cisco Systems, Inc.
Canada
Email: rgandhi@cisco.com
Royi Zigler (editor)
Broadcom
Email: royi.zigler@broadcom.com
Haoyu Song (editor)
Futurewei Technologies
Email: haoyu.song@futurewei.com
Kireeti Kompella (editor)
Juniper Networks
United States
Email: kireeti.ietf@gmail.com
Rajamanickam, et al. Expires 14 July 2023 [Page 30]
