]> University of Tuebingen

Tuebingen Germany fabian.ihle@uni-tuebingen.de

ZTE Corporation

China song.xueyan2@zte.com.cn

University of Tuebingen

Tuebingen Germany michael.menth@uni-tuebingen.de

Routing Multiprotocol Label Switching signaling mpls mna This document defines capabilities of nodes supporting MPLS Network Actions (MNA) and how to signal them using IS-IS and OSPF. The capabilities include the Readable Label Depth (RLD), supported network action opcodes, and the maximum sizes of differently scoped Network Action Sub-stacks (NAS), called the NAS_MLD. For IS-IS and OSPF signaling, sub-TLV encodings based on existing mechanisms to signal node- and link-specific capabilities are leveraged. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Multiprotocol Label Switching Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction With the MPLS Network Action (MNA) framework, network actions are encoded in the MPLS stack. Those can be added to the MPLS tack using in-stack data (ISD), or follow after the MPLS stack using post-stack data (PSD). defines the encoding of such network actions and their data for ISD in a so-called Network Action Substack (NAS). These network actions are processed by all nodes on a path (hop-by-hop, HBH), by only selected nodes, or on an ingress-to-egress (I2E) basis. LSRs have different capabilites that depend on available hardware resources, e.g., the number of LSEs they can parse. An ingress LER that pushes network actions to an MPLS stack MUST ensure that all nodes on the path can read and support the network actions. For that purpose, the MNA capabilities of an LSR need to be signaled to the ingress LER. This document defines the required parameters of LSRs regarding their MNA capability and proposes a signaling extension using an IGP such as IS-IS and OSPF.

Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Abbreviations This document makes use of the terms defined in and in .

Definition of MNA Capabilities This section defines the parameters that an LSR uses to signal its MNA capabilities to the ingress LER.

The Readable Label Depth (RLD) The Readable Label Depth (RLD) is the number of LSEs an LSR can parse without performance impact . An LSR is required to search the MPLS stack for NAS that have to be processed by the LSR. To that end, the network actions must be within the RLD of the node. For HBH-scoped network actions, the ingress LER that pushes the network actions MUST ensure that the actions are readable at each LSR on the path, i.e., that it is placed within the RLD of each node.

Example An example for the RLD parameter is given in . With an RLD of 5, an LSR is capable of reading labels A, B, C, D, and E but not F. An RLD of 8 is required in this example to read the entire MPLS stack.

Example MPLS stack of 8 MPLS LSEs illustrating the concept of RLD.

Maximum NAS Sizes This section gives a motivation for signaling maximum NAS sizes and then introduces the NAS Maximum Label Depth (NAS_MLD).

Motivation A NAS in the MNA header encoding is at least 2 LSEs and at most 17 LSEs large . At an LSR, one or more NAS, e.g., a select-scoped and a hop-by-hop-scoped NAS, are possible. With two maximum-sized NAS, an LSR is required to reserve 34 LSEs in hardware to be able to process network actions. This consumes hardware resources that may be needed to encode other LSEs, e.g., forwarding labels for SR-MPLS paths, or are not available in less capable devices. Many use cases in the MNA framework do not require a maximum-sized NAS of 17 LSEs to encode network actions and their ancillary data. Therefore, a NAS can be up to 17 LSEs but nodes can also support smaller maximum NAS. By signaling the maximum supported NAS size to the ingress LER, an LSR receiving packets with a larger NAS than supported is avoided. This way, the allocated resources for NAS can be reduced if smaller maximum NAS are supported. More resources are available for other purposes, and hardware with a low RLD can be made MNA-capable .

NAS Maximum Label Depth (NAS_MLD) The maximum supported number of LSEs in a NAS that an LSR can process is referred to as NAS Maximum Label Depth (NAS_MLD) in this document. For each scope in MNA, a separate parameter for the NAS_MLD exists, called NAS_MLD_Select, NAS_MLD_HBH, and NAS_MLD_I2E. An LSR SHOULD signal the maximum-supported size of a NAS for each scope, i.e., the parameters NAS_MLD_Select, NAS_MLD_HBH, and NAS_MLD_I2E. Those parameters include the Format A, B, C, and D LSEs from in a NAS. Based on the signaled parameters, the ingress LER MUST ensure the following when pushing the MPLS stack and NAS on a packet:

• The ingress LER MUST NOT push a select-scoped NAS that is larger than the signaled NAS_MLD_Select value of the node that will process the select-scoped NAS.
• The ingress LER MUST NOT push an HBH-scoped NAS that is larger than the minimum of all signaled NAS_MLD_HBH values of all nodes on the path.
• The ingress LER MUST NOT push an I2E-scoped NAS that is larger than the signaled NAS_MLD_I2E value of the egress node.

Example illustrates the different NAS_MLD sizes in an MPLS stack that are signaled to the LSR. In this example, a select-scoped NAS has a maximum size of 4 LSEs, a hop-by-hop-scoped NAS of 7 LSEs, and an I2E-scoped NAS of 4 LSEs.

Example MPLS stack illustrating the different NAS sizes.

Supported Network Action Opcodes An LSR MUST signal the network action opcodes it supports. If a network action opcode is not signaled, it is assumed that this opcode is not supported by the node.

Signaling MNA Capabilites This section defines a method for IGP routers to advertise the maximum supported numbers of LSEs in I2E-scoped NAS, select-scoped NAS, and HBH-scoped NAS, i.e., the per-scope NAS_MLD, the RLD, and supported opcodes.

Using IS-IS This section defines the signaling of the RLD and the NAS_MLD that can be supported for specific NAS using IS-IS node and link advertisement. defines the IS-IS Router Capability TLV that supports optional sub-TLVs to signal capabilities. Further, introduces a sub-TLV for node- and link-specific advertisement based on . They are used to signal MNA capabilities with IS-IS.

NAS_MLD Advertisement To signal the per-scope NAS_MLD, this document introduces new sub-TLVs based on . The NAS_MLD Sub-TLV is defined node- or link-specific as below:

NAS_MLD Sub-TLV for IS-IS signaling.

• Type:
  • 15 (link-specifc)
  • 23 (node-specific)
• Length: variable (multiple of 2 octets); represents the total length of the Value field
• Value: field consists of one or more pairs of a 1-octet MSD-Type and 1-octet MSD-Value
  • NAS_MLD-Type: value defined in the "IGP MSD-Types" registry created by the IANA Considerations section of this document (I2E, HBH, or Select).
  • NAS_MLD-Value: number in the range of 2-17.

This sub-TLV is optional. The scope of the advertisement is specific to the deployment.

RLD Advertisment For the RLD advertisement, a sub-TLV based on is requested in .

Supported Network Action Opcodes tbd

Using OSPF This section defines the signaling of the RLD and the NAS_MLD that can be supported for specific NAS using OSPF node and link advertisement. defines the OSPF RI Opaque LSA which is used in to carry the node-specific provisioned SID depth of the router originating the Router Information (RI) LSA in a sub-TLV. Further, defines link-specific advertisements using the optional sub-TLV of the OSPFv2 Extended Link TLV for OSPFv2, and defines link-specific advertisements using the optional sub-TLV of the E-Router-LSA TLV.

NAS_MLD Advertisement To signal the per-scope NAS_MLD, this document introduces new sub-TLVs based on , , and . The NAS_MLD Sub-TLV is defined node- or link-specific as below:

NAS_MLD Sub-TLV for OSPF signaling.

• Type:
  • 6 (link-specific, OSPFv2 )
  • 9 (link-specific, OSPFv3 )
  • 12 (node-specific, OSPFv2 and OSPFv3 )
• Length: variable (in octets); represents the total length of the Value field
• Value: field consists of one or more pairs of a 2-octet MSD-Type and 2-octet MSD-Value
  • NAS_MLD-Type: value defined in the "IGP MSD-Types" registry created by the IANA Considerations section of this document (I2E, HBH, or Select).
  • NAS_MLD-Value: number in the range of 2-17.

This sub-TLV is optional. The scope of the advertisement is specific to the deployment.

RLD Advertisment For the RLD advertisement, a sub-TLV is requested in .

Supported Network Action Opcodes tbd

Security Considerations The security issues discussed in , , and apply to this document.

IANA Considerations This document requests the allocation of following codepoints in the "IGP MSD-Types" registry. IGP Signaling Sub-TLV allocation.

Value	Name	Data Plane	Reference
3	Readable Label Depth	MPLS
4	MLD of select-scoped NAS	MPLS	This document
5	MLD of I2E-scoped NAS	MPLS	This document
6	MLD of HBH-scoped NAS	MPLS	This document

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References University of Tuebingen University of Tuebingen Cisco Systems, Inc. Cisco Systems, Inc. Broadcom Futurewei Technologies Juniper Networks This document defines the MPLS Network Actions (MNA) sub-stack solution for carrying Network Actions and Ancillary Data in the label stack. MNA can be used to influence packet forwarding decisions, carry additional Operations, Administration, and Maintenance information in the MPLS packet or perform user-defined operations. This solution document specifies In-stack network action and In-stack data specific requirements found in "Requirements for MPLS Network Actions". This document follows the architectural framework for the MNA technologies specified in "MPLS Network Actions (MNA) Framework". Huawei Technologies University of Surrey 5GIC Nokia Juniper Networks This document describes an architectural framework for the MPLS Network Actions (MNA) technologies. MNA technologies are used to indicate actions that impact the forwarding or other processing (such as monitoring) of the packet along the Label Switched Path (LSP) of the packet and to transfer any additional data needed for these actions. The document provides the foundation for the development of a common set of network actions and information elements supporting additional operational models and capabilities of MPLS networks. Cisco Systems, Inc. Independent Futurewei Technologies Ericsson This document presents use cases that have a common feature that may be addressed by encoding network action indicators and associated ancillary data within MPLS packets. There is community interest in extending the MPLS data plane to carry such indicators and ancillary data to address the use cases that are described in this document. The use cases described in this document are not an exhaustive set, but rather the ones that are actively discussed by members of the IETF MPLS, PALS, and DetNet working groups from the beginning of work on the MPLS Network Action until the publication of this document. This document defines a new optional Intermediate System to Intermediate System (IS-IS) TLV named CAPABILITY, formed of multiple sub-TLVs, which allows a router to announce its capabilities within an IS-IS level or the entire routing domain. This document obsoletes RFC 4971. This document defines a way for an Intermediate System to Intermediate System (IS-IS) router to advertise multiple types of supported Maximum SID Depths (MSDs) at node and/or link granularity. Such advertisements allow entities (e.g., centralized controllers) to determine whether a particular Segment ID (SID) stack can be supported in a given network. This document only defines one type of MSD: Base MPLS Imposition. However, it defines an encoding that can support other MSD types. This document focuses on MSD use in a network that is Segment Routing (SR) enabled, but MSD may also be useful when SR is not enabled. Huawei Technologies University of Surrey 5GIC Nokia Juniper Networks This document describes an architectural framework for the MPLS Network Actions (MNA) technologies. MNA technologies are used to indicate actions that impact the forwarding or other processing (such as monitoring) of the packet along the Label Switched Path (LSP) of the packet and to transfer any additional data needed for these actions. The document provides the foundation for the development of a common set of network actions and information elements supporting additional operational models and capabilities of MPLS networks. It is useful for routers in an OSPFv2 or OSPFv3 routing domain to know the capabilities of their neighbors and other routers in the routing domain. This document proposes extensions to OSPFv2 and OSPFv3 for advertising optional router capabilities. The Router Information (RI) Link State Advertisement (LSA) is defined for this purpose. In OSPFv2, the RI LSA will be implemented with an Opaque LSA type ID. In OSPFv3, the RI LSA will be implemented with a unique LSA type function code. In both protocols, the RI LSA can be advertised at any of the defined flooding scopes (link, area, or autonomous system (AS)). This document obsoletes RFC 4970 by providing a revised specification that includes support for advertisement of multiple instances of the RI LSA and a TLV for functional capabilities. This document defines a way for an Open Shortest Path First (OSPF) router to advertise multiple types of supported Maximum SID Depths (MSDs) at node and/or link granularity. Such advertisements allow entities (e.g., centralized controllers) to determine whether a particular Segment Identifier (SID) stack can be supported in a given network. This document only refers to the Signaling MSD as defined in RFC 8491, but it defines an encoding that can support other MSD types. Here, the term "OSPF" means both OSPFv2 and OSPFv3. OSPFv2 requires functional extension beyond what can readily be done with the fixed-format Link State Advertisements (LSAs) as described in RFC 2328. This document defines OSPFv2 Opaque LSAs based on Type-Length-Value (TLV) tuples that can be used to associate additional attributes with prefixes or links. Depending on the application, these prefixes and links may or may not be advertised in the fixed-format LSAs. The OSPFv2 Opaque LSAs are optional and fully backward compatible. OSPFv3 requires functional extension beyond what can readily be done with the fixed-format Link State Advertisement (LSA) as described in RFC 5340. Without LSA extension, attributes associated with OSPFv3 links and advertised IPv6 prefixes must be advertised in separate LSAs and correlated to the fixed-format LSAs. This document extends the LSA format by encoding the existing OSPFv3 LSA information in Type-Length-Value (TLV) tuples and allowing advertisement of additional information with additional TLVs. Backward-compatibility mechanisms are also described. This document updates RFC 5340, "OSPF for IPv6", and RFC 5838, "Support of Address Families in OSPFv3", by providing TLV-based encodings for the base OSPFv3 unicast support and OSPFv3 address family support. OSPFv2 requires functional extension beyond what can readily be done with the fixed-format Link State Advertisements (LSAs) as described in RFC 2328. This document defines OSPFv2 Opaque LSAs based on Type-Length-Value (TLV) tuples that can be used to associate additional attributes with prefixes or links. Depending on the application, these prefixes and links may or may not be advertised in the fixed-format LSAs. The OSPFv2 Opaque LSAs are optional and fully backward compatible. OSPFv3 requires functional extension beyond what can readily be done with the fixed-format Link State Advertisement (LSA) as described in RFC 5340. Without LSA extension, attributes associated with OSPFv3 links and advertised IPv6 prefixes must be advertised in separate LSAs and correlated to the fixed-format LSAs. This document extends the LSA format by encoding the existing OSPFv3 LSA information in Type-Length-Value (TLV) tuples and allowing advertisement of additional information with additional TLVs. Backward-compatibility mechanisms are also described. This document updates RFC 5340, "OSPF for IPv6", and RFC 5838, "Support of Address Families in OSPFv3", by providing TLV-based encodings for the base OSPFv3 unicast support and OSPFv3 address family support.