]> Cisco Systems, Inc.

tsaad.net@gmail.com

Futurewei Technologies

kiranm@futurewei.com

Futurewei Technologies

haoyu.song@futurewei.com

Ericsson

gregimirsky@gmail.com

MPLS Working Group Internet-Draft This document presents a number of use cases that have a common need for encoding network action indicators and associated ancillary data inside MPLS packets. There has been significant recent interest in extending the MPLS data plane to carry such indicators and ancillary data to address a number of 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 participating in the MPLS Open Design Team.

Introduction This document describes important cases that require carrying additional ancillary data within the MPLS packets, as well as means to indicate the ancillary data is present, and a specific action needs to be performed on the packet. These use cases have been identified by the MPLS Working Group Open Design Team working on defining MPLS Network Actions for the MPLS data plane. The MPLS Ancillary Data (AD) can be classified as: implicit, or "no-data" associated with a Network Action (NA) indicator, residing within the MPLS label stack and referred to as In Stack Data (ISD), and residing after the Bottom of MPLS label Stack (BoS) and referred to as Post Stack Data (PSD). The use cases described in this document will be used to assist in identifying requirements and issues to be considered for future resolution by the working group.

Terminology The following terminology is used in the document:

IETF Network Slice:

a well-defined composite of a set of endpoints, the connectivity requirements between subsets of these endpoints, and associated requirements; the term 'network slice' in this document refers to 'IETF network slice' as defined in .

Time-Bound Networking:

Networks that transport time-bounded traffic.

Acronyms and Abbreviations

• ISD: In-stack data

• PSD: Post-stack data

• MNA: MPLS Network Action

• NAI: Network Action Indicator

• AD: Ancillary Data

Use Cases

No Further Fastreroute MPLS Fast Reroute (FRR) , and is a useful and widely deployed tool for minimizing packet loss in the case of a link or node failure. Several cases exist where, once FRR has taken place in an MPLS network and resulted in rerouting a packet away from the failure, a second FRR that impacts the same packet to rerouting is not helpful, and may even be disruptive. For example, in such a case, the packet may continue to loop until its TTL expires. This can lead to link congestion and further packet loss. Thus, the attempt to prevent a packet from being dropped may instead affect many other packets. A proposal to address this is presented in .

In-situ OAM In-situ Operations, Administration, and Maintenance (IOAM) is used to collect operational and telemetry information while packets traverses a particular path in a network domain. The term "in-situ" refers to the fact that the IOAM data fields are added to the data packets rather than being sent within the probe packets specifically dedicated to OAM or Performance Measurement (PM). IOAM can run in two modes Edge-to-Edge (E2E) and Hop-by-Hop (HbH). In E2E mode, only the encapsulating and decapsulating nodes will process IOAM data fields. In HbH mode, the encapsulating and decapsulating nodes as well as intermediate IOAM-capable nodes process IOAM data fields. The IOAM data fields are defined in , and can be used for various OAM use-cases. Several IOAM Options have been defined: Pre-allocated and Incremental Edge-to-Edge Proof-of-Transit Direct Export (see ) defines how IOAM data fields are transported using the MPLS data plane encapsulations, including Segment Routing (SR) with MPLS data plane (SR-MPLS). The IOAM data may be added after the bottom of the MPLS label stack. The IOAM data fields can be of fixed or incremental size as defined in . describes the applicability of IOAM to MPLS dataplane. The encapsulating MPLS node needs to know if the decapsulating MPLS node can process the IOAM data before adding it in the packet. In HbH IOAM mode, nodes that are capable of processing IOAM will intercept and process the IOAM data accordingly. The presence of IOAM header and optional IOAM data will betransparent to nodes that do not support or do not participate in the IOAM process.

In-situ OAM Direct Export IOAM Direct Export (DEX) is an IOAM Option-Type in which the operational state and telemetry information is collected according to the specified profile and exported in a manner and format defined by a local policy. In IOAM DEX, the user data packet is only used to trigger the IOAM data to be directly exported or locally aggregated without being pushed into in-flight data packets.

Network Slicing An IETF Network Slice service provides connectivity coupled with a set of network resource commitments and is expressed in terms of one or more connectivity constructs. A slice-flow aggregate refers to the set of traffic streams from one or more connectivity constructs belonging to one or more IETF Network Slices that are mapped to a set of network resources and provided the same forwarding treatment. The packets associated with a slice-flow aggregate may carry a marking in the packet's network layer header to identify this association and this marking is referred to as Flow-Aggregate Selector (FAS). The FAS is used to map the packet to the associated set of network resources and provide the corresponding forwarding treatment to the packet. A router that requires forwarding of a packet that belongs to a slice-flow aggregate may have to decide on the forwarding action to take based on selected next-hop(s), and the forwarding treatment (e.g., scheduling and drop policy) to enforce based on the associated per-hop behavior. In this case, the routers that forward traffic over resources that are shared by multiple slice-flow aggregates need to identify the slice aggregate packets in order to enforce the associated forwarding action and treatment. MNA can be used to indicate the action and carry ancillary data for packets traversing Label Switched Paths (LSPs). An MNA network action can be used to carry the FAS in MPLS packets.

Dedicated Identifier as Flow-Aggregate Selector A dedicated Identifier that is independent of forwarding can be carried in the packet as a Flow-Aggregate Selector (FAS). This can be encoded in the MPLS packet as defined in , , and . The FAS is used to associate the packets belonging to Slice-Flow Aggregate to the underlying Network Resource Partition (NRP) as described in . When MPLS packets carry a dedicated FAS identifier, the MPLS LSRs use the forwarding label to select the forwarding next-hop(s), and use the FAS in the MPLS packet to infer the specific forwarding treatment that needs to be applied on the packet. The FAS can be encoded within an MPLS label carried in the packet's MPLS label stack. All MPLS packets that belong to the same flow aggregate MAY carry the same FAS identifier.

Forwarding Label as a Flow-Aggregate Selector states in Section 2.1 that: 'Some routers analyze a packet's network layer header not merely to choose the packet's next hop, but also to determine a packet's "precedence" or "class of service"'. It is possible by assigning a unique MPLS forwarding label to each flow aggregate (FEC) to distinguish the packets forwarded to the same destination. from other flow aggregates. In this case, LSRs can use the top forwarding label to infer both the forwarding action and the forwarding treatment to be invoked on the packets.

Generic Delivery Functions The Generic Delivery Functions (GDF), defined in , provide a new mechanism to support functions analogous to those supported through the IPv6 Extension Headers mechanism. For example, GDF can support fragmentation/reassembly functionality in the MPLS network by using the Generic Fragmentation Header. MNA can support GDF by placing a GDF header in an MPLS packet within the Post-Stack Data block . Multiple GDF headers can also be present in the same MPLS packet organized as a list of headers.

Delay Budgets for Time-Bound Applications The routers in a network can perform two distinct functions on incoming packets, namely forwarding (where the packet should be sent) and scheduling (when the packet should be sent). IEEE-802.1 Time Sensitive Networking (TSN) and Deterministic Networking provide several mechanisms for scheduling under the assumption that routers are time-synchronized. The most effective mechanisms for delay minimization involve per-flow resource allocation. Segment Routing (SR) is a forwarding paradigm that allows encoding forwarding instructions in the packet in a stack data structure, rather than being programmed into the routers. The SR instructions are contained within a packet in the form of a First-in First-out stack dictating the forwarding decisions of successive routers. Segment routing may be used to choose a path sufficiently short to be capable of providing a bounded end-to-end latency but does not influence the queueing of individual packets in each router along that path. When carried over the MPLS data plane, a solution is required to enable the delivery of such packets that can be delivered to their final destination by a given time budget. One approach to address this usecase in SR-MPLS was described in .

Stack Based Methods for Latency Control One efficient data structure for inserting local deadlines into the headers is a "stack", similar to that used in Segment Routing to carry forwarding instructions. The number of deadline values in the stack equals the number of routers the packet needs to traverse in the network, and each deadline value corresponds to a specific router. The Top-of-Stack (ToS) corresponds to the first router's deadline while the Bottom-of-Stack (BoS) refers to the last's. All local deadlines in the stack are later or equal to the current time (upon which all routers agree), and times closer to the ToS are always earlier or equal to times closer to the BoS. The ingress router inserts the deadline stack into the packet headers; no other router needs to be aware of the requirements of the time-bound flows. Hence admitting a new flow only requires updating the information base of the ingress router. MPLS LSRs that expose the Top of Stack (ToS) label can also inspect the associated "deadline" carried in the packet (either in MPLS stack as ISD or after BoS as PSD).

NSH-based Service Function Chaining describes how Service Function Chaining (SFC) can be realized in an MPLS network by emulating the NSH by using only MPLS label stack elements. The approach in introduces some limitations that are discussed in . This approach, however, can benefit from the framework introduced with MNA in . For example, it may be possible to extend NSH emulation using MPLS labels to support the functionality of NSH Context Headers, whether fixed or variable-length. One of the use cases could support Flow ID that may be used for load-balancing among Service Function Forwarders (SFFs) and/or the Service Function (SF) within the same SFP.

Network Programming In SR, an ingress node steers a packet through an ordered list of instructions, called "segments". Each one of these instructions represents a function to be called at a specific location in the network. A function is locally defined on the node where it is executed and may range from simply moving forward in the segment list to any complex user-defined behavior. Network Programming combines Segment Routing (SR) functions to achieve a networking objective that goes beyond mere packet routing. It may be desirable to encode a pointer to function and its arguments within an MPLS packet transport header. For example, in MPLS we can encode the FUNC::ARGs within the label stack or after the Bottom of Stack to support the equivalent of FUNC::ARG in SRv6 as described in .

Existing MPLS Use cases There are serveral services that can be transported over MPLS networks today. These include providing Layer-3 (L3) connectivity (e.g. for unicast and multicast L3 services), and Layer-2 (L2) connectivity (e.g. for unicast Pseudo-Wires (PWs), multicast E-Tree, and broadcast E-LAN L2 services). In those cases, the user service traffic is encapsulated as the payload in MPLS packets. For L2 service traffic, it is possible to use A Control Word (CW) and immediately after the MPLS header to disambiguate the type of MPLS payload, prevent possible packet misordering, and allow for fragmentation. In this case, the first nibble the data that immediately follows after MPLS bottom of stack is set to 0000b to identify the presence of PW CW. In addition to providing connectivity to user traffic, MPLS may also transport OAM data (e.g. over MPLS G-AChs ). In this case, the first nibble of the data that immediately follows after MPLS bottom of stack is set to 0001b, it indicates the presence of a control channel associated witha PW, LSP, or Section. Bit Index Explicit Replication (BIER) traffic can also be encapsulated over MPLS. In this case, BIER has defined 0101b as the value for the first nibble in the data that immediately appears after the bottom of the label stack for any BIER encapsulated packet over MPLS. For pseudowires, the G-ACh uses the first four bits of the PW control word to provide the initial discrimination between data packets and packets belonging to the associated channel, as described in . It is expected that new use cases described in this document and within the MNA framework will allow for the co-existance and backward compatibility with all such existing MPLS services.

Co-existence of Usecases Two or more of the aforementioned use cases MAY co-exist in the same packet. This may require the presence of multiple ancilary data (whether In-stack or Post-stack ancillary data) to be present in the same MPLS packet. For example, IOAM may provide key functions along with network slicing to help ensure that critical network slice SLOs are being met by the network provider. In this case, IOAM is able to collect key performance measurement parameters of network slice traffic flows as it traverses the transport network.

IANA Considerations This document has no IANA actions.

Security Considerations This document introduces no new security considerations.

Acknowledgement The authors gratefully acknowledge the input of the members of the MPLS Open Design Team.

Contributors The following individuals contributed to this document:

Old Dog Consulting Juniper Networks Ciena NTT Futurewei Telefonica Microsoft Inc. This document describes network slicing in the context of networks built from IETF technologies. It defines the term "IETF Network Slice" and establishes the general principles of network slicing in the IETF context. The document discusses the general framework for requesting and operating IETF Network Slices, the characteristics of an IETF Network Slice, the necessary system components and interfaces, and how abstract requests can be mapped to more specific technologies. The document also discusses related considerations with monitoring and security. This document also provides definitions of related terms to enable consistent usage in other IETF documents that describe or use aspects of IETF Network Slices. This document defines RSVP-TE extensions to establish backup label-switched path (LSP) tunnels for local repair of LSP tunnels. These mechanisms enable the re-direction of traffic onto backup LSP tunnels in 10s of milliseconds, in the event of a failure.Two methods are defined here. The one-to-one backup method creates detour LSPs for each protected LSP at each potential point of local repair. The facility backup method creates a bypass tunnel to protect a potential failure point; by taking advantage of MPLS label stacking, this bypass tunnel can protect a set of LSPs that have similar backup constraints. Both methods can be used to protect links and nodes during network failure. The described behavior and extensions to RSVP allow nodes to implement either method or both and to interoperate in a mixed network. [STANDARDS-TRACK] This document describes the use of loop-free alternates to provide local protection for unicast traffic in pure IP and MPLS/LDP networks in the event of a single failure, whether link, node, or shared risk link group (SRLG). The goal of this technology is to reduce the packet loss that happens while routers converge after a topology change due to a failure. Rapid failure repair is achieved through use of precalculated backup next-hops that are loop-free and safe to use until the distributed network convergence process completes. This simple approach does not require any support from other routers. The extent to which this goal can be met by this specification is dependent on the topology of the network. [STANDARDS-TRACK] This document describes an extension to the basic IP fast reroute mechanism, described in RFC 5286, that provides additional backup connectivity for point-to-point link failures when none can be provided by the basic mechanisms. Juniper Networks Juniper Networks There are several cases where, once Fast Reroute has taken place (for MPLS protection), a second fast reroute is undesirable, even detrimental. This memo gives several examples of this, and proposes a mechanism to prevent further fast reroutes. Cisco Systems, Inc. Thoughtspot Huawei In situ Operations, Administration, and Maintenance (IOAM) collects operational and telemetry information in the packet while the packet traverses a path between two points in the network. This document discusses the data fields and associated data types for IOAM. IOAM-Data-Fields can be encapsulated into a variety of protocols, such as Network Service Header (NSH), Segment Routing, Generic Network Virtualization Encapsulation (Geneve), or IPv6. IOAM can be used to complement OAM mechanisms based on, e.g., ICMP or other types of probe packets. Cisco Systems, Inc. Cisco Systems, Inc. Cisco Systems, Inc. Cisco Systems, Inc. Comcast Comcast In-situ Operations, Administration, and Maintenance (IOAM) records operational and telemetry information in the data packet while the packet traverses a path between two nodes in the network. This document defines how IOAM data fields are transported with MPLS data plane encapsulation using new Generic Associated Channel (G-ACh). Cisco Systems, Inc. Cisco Systems, Inc. Comcast Orange Futurewei Technologies In Situ Operations, Administration, and Maintenance (IOAM) is used for recording and collecting operational and telemetry information while the packet traverses a path between two points in the network. This document defines how IOAM data fields are transported with MPLS data plane encapsulation using MPLS Network Action (MNA). Futurewei Nvidia Cisco Thoughtspot Huawei In situ Operations, Administration, and Maintenance (IOAM) is used for recording and collecting operational and telemetry information. Specifically, IOAM allows telemetry data to be pushed into data packets while they traverse the network. This document introduces a new IOAM option type (denoted IOAM-Option-Type) called the "IOAM Direct Export (DEX) Option-Type". This Option-Type is used as a trigger for IOAM data to be directly exported or locally aggregated without being pushed into in-flight data packets. The exporting method and format are outside the scope of this document. Juniper Networks Juniper Networks Huawei Technologies Comcast Ericsson Ericsson ZTE Corporation ZTE Corporation Volta Networks Telefonica Ciena Verizon Realizing network slices may require the Service Provider to have the ability to partition a physical network into multiple logical networks of varying sizes, structures, and functions so that each slice can be dedicated to specific services or customers. Multiple network slices can be realized on the same network while ensuring slice elasticity in terms of network resource allocation. This document describes a scalable solution to realize network slicing in IP/MPLS networks by supporting multiple services on top of a single physical network by relying on compliant domains and nodes to provide forwarding treatment (scheduling, drop policy, resource usage) on to packets that carry identifiers that indicate the slicing service that is to be applied to the packets. Juniper Networks Juniper Networks Juniper Networks Broadcom The MPLS architecture introduced Special Purpose Labels (SPLs) to indicate special forwarding actions and offered a few simple examples, such as Router Alert. In the two decades since the original architecture was crafted, the range, complexity and sheer number of such actions has grown; in addition, there now is need for "associated data" for some of the forwarding actions. Likewise, the capabilities and scale of forwarding engines has also improved vastly over the same time period. There is a pressing need to match the needs with the capabilities to deliver the next generation of MPLS architecture. In this memo, we propose an alternate mechanism whereby a single SPL can encode multiple forwarding actions and carry data (if any) associated with the actions, some in the label stack and some after the label stack. This proposal also solves the problem of scarcity of base SPLs. As proof of its utility and flexibility, this approach can immediately address several use cases: * to carry an Entropy Label for better load balancing; * to carry a Flow-Aggregate Selector for IETF network slicing; * to signal that further fast reroute may have harmful consequences; * to indicate that there is relevant data after the label stack; * among others. Huawei Technologies Huawei Technologies A Virtual Transport Network (VTN) is a virtual network which has a customized network topology and a set of dedicated or shared network resources allocated from the underlying physical network. Multiple VTNs can be created by network operator for using as the underlay for one or a group of VPNs services to provide enhanced VPN (VPN+) services. In packet forwarding, some fields in the data packet needs to be used to identify the VTN the packet belongs to, so that the VTN-specific processing can be executed on the packet. In the context of network slicing, a VTN can be instantiated as a Network Resource Partition (NRP). This document proposes a mechanism to carry the data plane VTN ID in an MPLS packet to identify the VTN the packet belongs to. The procedure for processing the VTN ID is also specified. Orange Cisco Systems, Inc. Nokia Juniper Networks Juniper Networks Verizon This document updates [RFC6790] to extend the use of the TTL field of the Entropy Label in order to provide a flexible set of flags called the Entropy Label Control field. This document also defines a solution to encode a slice identifier in MPLS in order to distinguish packets that belong to different slices, to allow enforcing per network slice policies (.e.g, Qos). The slice identification is independent of the topology. It allows for QoS/DiffServ policy on a per slice basis in addition to the per packet QoS/DiffServ policy provided by the MPLS Traffic Class field. In order to minimize the size of the MPLS stack and to ease incremental deployment the slice identifier is encoded as part of the Entropy Label. This document specifies the architecture for Multiprotocol Label Switching (MPLS). [STANDARDS-TRACK] Juniper Networks Juniper Networks Juniper Networks ZTE Some functionalities (e.g., fragmentation/reassembly and Encapsulating Security Payload) provided by IPv6 can be viewed as delivery functions independent of IPv6 or even IP entirely. This document proposes to provide those functionalities at different layers (e.g., MPLS, BIER or even Ethernet) independent of IP. Huawei Technologies University of Surrey 5GIC Nokia Juniper Networks This document specifies an architectural framework for the MPLS Network Actions (MNA) technologies. MNA technologies are used to indicate actions for Label Switched Paths (LSPs) and/or MPLS packets and to transfer data needed for these actions. The document describes a common set of network actions and information elements supporting additional operational models and capabilities of MPLS networks. Some of these actions are defined in existing MPLS specifications, while others require extensions to existing specifications to meet the requirements found in "Requirements for MPLS Network Action Indicators and Ancillary Data". RAD Routers perform two distinct user-plane functionalities, namely forwarding (where the packet should be sent) and scheduling (when the packet should be sent). One forwarding paradigm is segment routing, in which forwarding instructions are encoded in the packet in a stack data structure, rather than programmed into the routers. Time Sensitive Networking and Deterministic Networking provide several mechanisms for scheduling under the assumption that routers are time synchronized. The most effective mechanisms for delay minimization involve per-flow resource allocation. SRTSN is a unified approach to forwarding and scheduling that uses a single stack data structure. Each stack entry consists of a forwarding portion (e.g., IP addresses or suffixes) and a scheduling portion (deadline by which the packet must exit the router). SRTSN thus fully implements network programming for time sensitive flows, by prescribing to each router both to-where and by-when each packet should be sent. This document describes how Service Function Chaining (SFC) can be achieved in an MPLS network by means of a logical representation of the Network Service Header (NSH) in an MPLS label stack. That is, the NSH is not used, but the fields of the NSH are mapped to fields in the MPLS label stack. This approach does not deprecate or replace the NSH, but it acknowledges that there may be a need for an interim deployment of SFC functionality in brownfield networks. ZTE Ericsson This document describes extensions to MPLS LSP ping mechanisms to support verification between the control/management plane and the data plane state for SR-MPLS service programming and MPLS-based NSH SFC. This document defines the signaling of the Generic Associated Channel (G-ACh) over a Service Function Path (SFP) with an MPLS forwarding plane using the basic unit defined in RFC 8595. The document updates RFC 8595 in respect to SFF's handling TTL expiration. The document also describes the processing of the G-ACh by the elements of the SFP. ZTE Corporation Intel Individual contributor Cisco Futurewei Technologies Service Function Chaining (SFC) uses the Network Service Header (NSH) (RFC 8300) to steer and provide context metadata (MD) with each packet. Such metadata can be of various types, including MD Type 2, consisting of Variable-Length Context Headers. This document specifies several such Context Headers that can be used within a Service Function Path (SFP). The Segment Routing over IPv6 (SRv6) Network Programming framework enables a network operator or an application to specify a packet processing program by encoding a sequence of instructions in the IPv6 packet header.Each instruction is implemented on one or several nodes in the network and identified by an SRv6 Segment Identifier in the packet.This document defines the SRv6 Network Programming concept and specifies the base set of SRv6 behaviors that enables the creation of interoperable overlays with underlay optimization. This document describes the preferred design of a Pseudowire Emulation Edge-to-Edge (PWE3) Control Word to be used over an MPLS packet switched network, and the Pseudowire Associated Channel Header. The design of these fields is chosen so that an MPLS Label Switching Router performing MPLS payload inspection will not confuse a PWE3 payload with an IP payload. [STANDARDS-TRACK] This document describes Virtual Circuit Connectivity Verification (VCCV), which provides a control channel that is associated with a pseudowire (PW), as well as the corresponding operations and management functions (such as connectivity verification) to be used over that control channel. VCCV applies to all supported access circuit and transport types currently defined for PWs. [STANDARDS-TRACK] This document generalizes the applicability of the pseudowire (PW) Associated Channel Header (ACH), enabling the realization of a control channel associated to MPLS Label Switched Paths (LSPs) and MPLS Sections in addition to MPLS pseudowires. In order to identify the presence of this Associated Channel Header in the label stack, this document also assigns one of the reserved MPLS label values to the Generic Associated Channel Label (GAL), to be used as a label based exception mechanism. Bit Index Explicit Replication (BIER) is an architecture that provides optimal multicast forwarding through a "multicast domain", without requiring intermediate routers to maintain any per-flow state or to engage in an explicit tree-building protocol. When a multicast data packet enters the domain, the ingress router determines the set of egress routers to which the packet needs to be sent. The ingress router then encapsulates the packet in a BIER header. The BIER header contains a bit string in which each bit represents exactly one egress router in the domain; to forward the packet to a given set of egress routers, the bits corresponding to those routers are set in the BIER header. The details of the encapsulation depend on the type of network used to realize the multicast domain. This document specifies a BIER encapsulation that can be used in an MPLS network or, with slight differences, in a non-MPLS network.