| Internet-Draft | MNA Sub-Stack | March 2023 |
| Rajamanickam, et al. | Expires 30 September 2023 | [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 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.¶
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This Internet-Draft will expire on 30 September 2023.¶
Copyright (c) 2023 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 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].¶
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] are 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 | 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 And Management | [RFC4377] |
| 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 encapsulated packet. Multiple NASes may appear in a label stack.¶
Network actions and their optional Ancillary Data (AD) may be encoded as part of the NAS as a series 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 a traditional LSE, as described in [RFC3032] and [RFC5462].¶
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 |R|IHS|S| Res |U| NASL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.¶
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.¶
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).¶
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.¶
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 (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.¶
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.¶
| Bit | Action |
|---|---|
| 0 | Skip to the next NA |
| 1 | Drop the packet |
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.¶
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 |R|IHS|S| Res |U| NASL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A more complex NAS might have multiple opcodes and additional Ancillary Data. This example has two opcodes and two additional LSEs of 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 | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode | Data |R|IHS|S| Res |U| NASL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode | Data |S| Data | NAL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1| Data |S| Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1| Data |S| Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In this example, the NASL field would have value 3 and the NAL field would have value 2.¶
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: 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.¶
Opcode: 127¶
Purpose: This opcode is reserved to extend the current opcode range beyond 127. Future use of this opcode is out of scope.¶
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.¶
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.¶
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.¶
The above capability signaling will be added in appropriate protocols. Signaling details are outside the scope of this document.¶
This section defines the specific responsibilities for nodes along a MPLS path.¶
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.¶
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.¶
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.¶
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.¶
The decapsulating node MUST remove any NAS it receives.¶
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:¶
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.¶
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.¶
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 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 |
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 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 |
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:¶
| Opcode | Description | Reference |
|---|---|---|
| 0 | Reserved | This document |
| 1 | Reserved | This document |
| 2 | Flag-Based Network Action Indicators without AD | This document |
| 3-110 | Unassigned | |
| 111-126 | Private Use | |
| 127 | Opcode Range Extension Beyond 127 | This document |
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 |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 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 |R|IHS|S| Res |U| NASL=2| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=2 | 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 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 |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 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 |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 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 |R|IHS|S|Res|U|1| NASL=2| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=7 | Ancillary Data7 |S| AD7 | NAL=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode=2 | 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 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 |R|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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.¶
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.¶
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