| Internet-Draft | MNA Sub-Stack Solution | June 2024 |
| Rajamanickam, et al. | Expires 7 December 2024 | [Page] |
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 Operations, Administration, and Maintenance (OAM) information in the MPLS packet or perform user-defined operations. This solution document specifies In-stack network action and In-stack data (ISD) specific requirements found in "Requirements for MPLS Network Actions". This document follows the architectural framework for the MPLS Network Actions (MNA) technologies specified in "MPLS Network Actions (MNA) Framework".¶
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."¶
This Internet-Draft will expire on 7 December 2024.¶
Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
[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 Operations, Administration, and Maintenance (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.¶
Network actions can be encoded with or without Ancillary Data (AD), either in the label stack or after the label stack. This solution document specifies In-stack network action and In-stack data (ISD) specific requirements found in [I-D.ietf-mpls-mna-requirements].¶
This document defines the syntax and semantics of network actions and ancillary data encoded in an MPLS Label Stack. In-stack actions and ancillary data are contained in a Network Action Sub-Stack (NAS), which is recognized by a new base Special Purpose Label (bSPL). This document follows the framework specified in [I-D.ietf-mpls-mna-fwk].¶
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.¶
The terminology defined in [I-D.ietf-mpls-mna-fwk] and [I-D.ietf-mpls-mna-requirements] is used in this document.¶
| Abbreviation | Meaning | Reference |
|---|---|---|
| AD | Ancillary Data | [I-D.ietf-mpls-mna-requirements] |
| bSPL | Base Special Purpose Label | [RFC9017] |
| BOS | Bottom Of Stack | [RFC3032] |
| HBH | Hop-By-Hop Scope | [I-D.ietf-mpls-mna-fwk] |
| I2E | Ingress-To-Egress Scope | [I-D.ietf-mpls-mna-fwk] |
| IHS | I2E, HBH, or Select Scope | [I-D.ietf-mpls-mna-fwk], This document |
| ISD | In-stack Data | [I-D.ietf-mpls-mna-requirements] |
| LSE | Label Stack Entry | [RFC3032] |
| MNA | MPLS Network Actions | [I-D.ietf-mpls-mna-fwk] |
| NAI | Network Action Indicator | [I-D.ietf-mpls-mna-requirements] |
| NAL | Network Action Length | This document |
| NAS | Network Action Sub-Stack | [I-D.ietf-mpls-mna-fwk] |
| NASI | Network Action Sub-Stack Indicator | This document |
| NASL | Network Action Sub-Stack Length | This document |
| OAM | Operations, Administration, and Maintenance | [RFC6291] |
| RLD | Readable Label Depth | [I-D.ietf-mpls-mna-fwk] |
| TC | Traffic Class | [RFC5462] |
| TTL | Time To Live | [RFC3032] |
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 packet. Multiple NASes may appear in a label stack.¶
This document describes how network actions and their optional ancillary data are encoded as part of an NAS as a stack of LSEs.¶
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.¶
LSE Format A is an LSE as described in [RFC3032] and [RFC5462]. The label value is an IANA-assigned value (TBA) for the MNA bSPL label from the "Base Special-Purpose MPLS Label Values" registry to indicate the presence of an MNA Sub-Stack in the label stack.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MNA-Label=bSPL (TBA) | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LSE Format B is used to encode the first opcode in the NAS, plus a number of other fields about the NAS. This format cannot carry more than 13 bits of data.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode | Data |R|IHS|S| Res |U| NASL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NOTE: Format A and B LSEs MUST be present when a Format C LSE is to be carried in the NAS. Format A, B, and C LSEs MUST be present when one or more Format D LSEs are to be carried in the NAS.¶
LSE Format C is used to encode the subsequent opcodes in the NAS.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode | Data |S| Data | NAL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LSE Format D is used to encode additional data that did not fit in the LSE with the preceding opcode.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1| Data |S| Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 Format A LSE retain their semantics as defined in [RFC3032] and [RFC5462]. The TTL and TC fields in the Format A LSE are copied from the forwarding label at the top of the label stack. 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.¶
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.¶
An NAS MAY contain more Format C (Section 4.3) and Format D (Section 4.4) LSEs, up to the length encoded in the NASL value. All Format D LSEs MUST follow a Format C LSE and be included in that LSE's NAL value.¶
The opcode is a 7-bit field that indicates the semantics of its LSE. Several opcodes are assigned special semantics (Section 6), others act as Network Action Indicators and are assigned through IANA (Section 10 and Section 14.4).¶
The data field carries opcode specific data. This is ancillary data for a network action. In the case of opcode 1, data field carries Flag-Based Network Action Indicators without ancillary data.¶
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.¶
This is also applicable to opcode 1 Flag-Based Network Action Indicators those need to be changed in flight.¶
If a network action needs to encode more data that might need to change during packet forwarding it will need to use a stack of Format D LSEs (Section 4.3) (which may be inefficient) or post-stack ancillary data (which is beyond the scope of this document).¶
The IHS field in the Format B LSE indicates the scope of the In-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:¶
| Bits | Scope |
|---|---|
| 00 | I2E |
| 01 | HBH |
| 10 | Select |
| 11 | Reserved |
A single NAS carries only one of the three scopes (I2E/HBH/Select). To support multiple scopes for a single packet, multiple NASes MAY be included in a single label stack.¶
The egress node is included in the HBH scope. This implies that the penultimate node MUST NOT remove a HBH NAS. The egress node MAY receive a NAS at the top of the label stack as discussed in Section 10.¶
An I2E scope NAS, if present, MUST be encoded after any HBH or Select-scope NASes. This makes it easier for the transit nodes to process a NAS with HBH or Select scope.¶
The Unknown Network 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 Network Action Handling actions are defined below.¶
| Bit | Action |
|---|---|
| 0 | Skip to the next NA |
| 1 | Drop the packet |
When a packet with an unknown Network Action is dropped, the node SHOULD maintain a local counter for this event, and MAY send a rate-limited notification to the operator.¶
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 (see Section 6.2) MUST be processed as if they were processed from the most significant bit to the least significant bit. If a label stack contains multiple NASes, then they MUST be processed as if they were processed in the order that they appear in the label stack, subject to the restrictions in Section 7.¶
Below are the special opcodes used to build a basic In-stack MNA solution. In future, additional special opcodes can be defined and their code-points can be assigned from the "Network Action Opcodes" IANA registry.¶
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.¶
Opcode: 1¶
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 this opcode is used with LSE Format B only, then up to 13 flags may be carried. If this opcode is used with LSE Format C only, then up to 20 flags may be carried. Format D LSEs can be used with format C LSEs to encode more than 20 flags. Flags are assigned from the "Network Action Flags Without Ancillary Data" registry (Section 14.3). If flags need to be evaluated in a different order, multiple LSEs using this opcode may be used to specify the requested order.¶
Scope: This opcode can be used with any scope.¶
Opcode: 2¶
Purpose: This opcode is reserved to indicate that this opcode does not perform any Network Action and MUST be skipped.¶
Scope: Format B.¶
Opcode: 127¶
Purpose: This opcode is reserved to extend the current opcode range beyond 127 in future. If this opcode is not supported, then the packet with the opcode 127 MUST be dropped. Use of this opcode is outside the scope of this document.¶
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 downstream node along the path will have a Readable Label Depth (RLD) [I-D.ietf-mpls-mna-fwk]. If the NAS is to be processed by a downstream MNA-capable node, then the entire NAS MUST be placed so that it is within RLD by the time the packet reaches the downstream MNA-capable node and the NAS MUST NOT appear at the top of the stack at any MNA incapable node on the path.¶
If the label stack is deep, several copies of the NAS may need to be encoded in the label stack.¶
For a NAS with HBH scope, every node will process the top copy of the NAS.¶
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. The select-scoped NAS needs to be inserted after the forwarding label and needs to be inserted before the next forwarding label. It could be inserted before or after a HBH NAS.¶
For I2E scope, only one copy of the NAS needs to be added at the bottom of the stack.¶
Transit, non-penultimate nodes that pop a forwarding label and expose a copy of a NAS MUST remove it.¶
A node performing Penultimate Hop Popping (PHP) that pops the forwarding label with only the NAS(es) remaining on the stack MUST NOT remove the NAS(es). Instead, it forwards the packet with the NAS(es) at the top of stack to the next node.¶
The node that receives the NAS at the top of the label stack MUST remove it.¶
An MNA-capable node may need to push additional labels as well as push new network actions onto a received packet.¶
While pushing additional labels on to the label stack of the receive packet, the MNA-capable node MUST verify that the entire top-most NAS with HBH scope is still within the RLD of the downstream MNA-capable nodes. If required, the MNA-capable node MAY create a copy of the top-most NAS with HBH scope and insert it within the RLD of the downstream MNA-capable nodes on the label stack.¶
When an MNA-capable node needs to push a new NAS with HBH scope on to a received packet that already has an NAS with HBH scope, it SHOULD copy (and merge) the network actions (including their Ancillary Data) from the received top-most NAS with HBH scope in the new NAS with HBH scope. The new NAS MUST be placed within the RLD of the downstream MNA-capable nodes. This behavior can be based on local policy.¶
The new network actions added MUST NOT conflict with the network actions in the received NAS with HBH scope. The mechanism to resolve such conflicts depend on the network actions and can be based on local policy. The MNA-capable node that pushes entries MUST understand any network actions which it is pushing which may result in a conflict, and MUST resolve any conflicts between new and received network actions. In the usual case of a conflict of duplicating a network action, the definition of the network action will generally give guidance on likely resolutions.¶
Encapsulating Node is the node that pushes an NAS on to the Label stack.¶
The encapsulating node MUST make sure that the NAS can be processed by the transit and egress nodes.¶
This section defines the specific responsibilities for nodes along an LSP.¶
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 an NAS to the label stack if the egress node does not support MNA.¶
If there is an existing label stack, the encapsulating node MUST NOT change the first 20 bits of any LSE in the label stack to avoid ECMP path change.¶
If the encapsulating node is also a transit node, then it MUST also follow the rules set out in Section 9.2.¶
Transit Node is the node that process an NAS on to the Label stack but does not push any new NAS.¶
Transit nodes MUST NOT change the first 20 bits of any LSE in the label stack to avoid ECMP path change.¶
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, according to the rules set out in Section 5.5.¶
A transit node that processes an NAS and does not recognise the value of an opcode MUST follow the rules according to the setting of the Unknown Action Handling value in the NAS as described in (Section 5.4).¶
In addition to the transit node responsibilities, the penultimate node and penultimate SR-MPLS segment node MUST NOT remove the last copy of an HBH or I2E NAS when it is exposed after removing the forwarding (transport) label. This allows the egress node to process the NAS.¶
The egress node MUST remove any NAS it receives.¶
The following information MUST be defined for new Network Action Indicator opcode request in the document that specifies the Network Action.¶
A request for a new NAI MUST include the following information:¶
An assignment for an NAI MAY make requests from any combination of the "Network Action Opcodes" or "Network Action Flags Without Ancillary Data" assignments. This decision should optimize for eventual encoding efficiency. If the NAI does not require any ancillary data, then a flag is preferred as only one bit is used in the encoding.¶
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).¶
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.¶
This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [RFC7942]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist.¶
The solution defined in this document has been implemented using P4 pipeline. The implementation code could be found at https://github.com/uni-tue-kn/P4-MNA.¶
The security considerations in [RFC3032] also apply to this document.¶
In addition, MNA-creates a new dimension in security concerns:¶
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.¶
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.¶
This document requests that IANA create a new registry with the name "Network Action Flags Without Ancillary Data". Registration requests should comply with Section 10. The registration procedure for this registry is "IETF Review", "Experimental Use" and "Private Use" as defined in [RFC8126]. The fields in this registry are "Bit Position" (integer), "Description" (string), and "Reference" (string).¶
Bit Position refers to the position relative to the most significant bit in LSE Format B or C Data fields and any subsequent Format D LSEs. Bit Position 0 is the most significant bit in an LSE Format B or C Data field. Bit Position 20 is the most significant bit in the first LSE Format D Data field. There are 20 bits available in LSE Format C and 30 bits available in LSE Format D. There are at most 14 Format D LSEs per opcode (due to NASL limit of 15 and Format D requires Format C LSE), so there are at most 20 + 14 * 30 = 440 bit positions. The Bit Position is an integer with value 0-469.¶
The initial assignments for this registry are:¶
| Bit Position | Description | Reference |
|---|---|---|
| 0-14 | IETF Review | This document |
| 15-16 | Experimental Use | This document |
| 17-19 | Private Use | This document |
| 20-469 | IETF Review | This document |
This document requests that IANA create a new registry with the name "Network Action Opcodes Registry". Registration requests should comply with Section 10. The registration procedure for this registry is "IETF Review", "Experimental Use" and "Private Use" as defined in [RFC8126]. The fields are "Opcode" (integer), "Description" (string), and "Reference" (string). Opcode is an integer with value 1-126.¶
| Opcode | Description | Reference |
|---|---|---|
| 1-110 | IETF Review | This document |
| 111-114 | Experimental Use | This document |
| 115-126 | Private Use | This document |
IANA has allocated values for the following Network Action Opcodes from "Network Action Opcode Registry".¶
| Opcode | Description | Reference |
|---|---|---|
| 0 | Reserved | This document |
| 1 | Flag-Based Network Action Indicators without AD | This document |
| 2 | No operation Opcode | This document |
| 127 | Opcode Range Extension Beyond 127 | This document |
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label=MNA bSPL | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=1 | Flags |R|IHS|S| Res |U| NASL=0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This is an example of an NAS with Flag-Based NAIs without Ancillary Data.¶
Details:¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label=MNA bSPL | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=1 | Data=0 |R|IHS|S| Res |U| NASL=2| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=1 | Flag-Based NAIs |0| NAIs | NAL=1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1| Additional Flag-Based NAIs |S|Flag-Based-NAIs| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MNA-Label=bSPL (TBA) | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=8 | Ancillary Data |R|IHS|S| Res |U| NASL=0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In this example, the NAS is carrying only one Network Action that requires 13 bits of Ancillary Data.¶
Details on the Second LSE¶
A network action may require more Ancillary Data than can fit in a single LSE. In this example, a Format D LSE is added to carry additional Ancillary Data.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label=MNA bSPL | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=1 | Data=0 |R|IHS|0| Res |U| NASL=2| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=9 | Ancillary Data |0| AD | NAL=1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1| Ancillary Data |S|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:¶
Details on the fourth LSE:¶
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.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label=MNA bSPL | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=8 | Ancillary Data |R|IHS|S|Res|U|1| NASL=2| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=7 | Ancillary Data7 |S| AD7 | NAL=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=1 | Flag-Based NAIs |S| NAI | NAL=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In this example, opcode 8 is processed first, then opcode 7, and then the network action flags are processed from most significant to least significant.¶
In a different case, some Flag-Based NAIs may need to be processed before opcode 7 and some Flag-Based NAIs may need to be processed after Opcode 7. This can be done by causing some NAIs to appear earlier in the NAS.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label=MNA bSPL | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=8 | Ancillary Data |R|IHS|S|Res|U|1| NASL=3| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=1 | 0x01 |S| NAI | NAL=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=7 | Ancillary Data7 |S| AD7 | NAL=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=1 | 0x02 |S| NAI | NAL=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In the above example, opcode 8 is processed first, then Flag-Based NAI 0x01 is processed, then opcode 7 is processed, and finally NAI 0x02 is processed.¶
The authors of this document would like to thank the MPLS Working Group Open Design Team for the discussions and comments on this document. The authors would also like to thank Amanda Baber for reviewing the IANA Considerations and providing many useful suggestions. The authors would like to thank Loa Andersson, Stewart Bryant, Greg Mirsky, Joel M. Halpern and Adrian Farrel for reviewing this document and providing many useful suggestions. The authors would like to thank Fabian Ihle and Michael Menth, both from University of Tuebingen, for implementing the solution defined in this document in P4 pipeline.¶
The following people have substantially contributed to this document:¶
Jisu Bhattacharya Cisco Systems, Inc. Email: jisu@cisco.com Bruno Decraene Orange Email: bruno.decraene@orange.com Weiqiang Cheng China Mobile Email: chengweiqiang@chinamobile.com Xiao Min ZTE Corp. Email: xiao.min2@zte.com.cn Luay Jalil Verizon Email: luay.jalil@verizon.com Jie Dong Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: jie.dong@huawei.com Tianran Zhou Huawei Technologies China Email: zhoutianran@huawei.com Bin Wen Comcast Email: Bin_Wen@cable.comcast.com Sami Boutros Ciena Email: sboutros@ciena.com Tony Li Juniper Networks United States Email: tony.li@tony.li John Drake Juniper Networks United States Email: jdrake@juniper.net