Juniper Networks

tsaad@juniper.net

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 MPLS function indicators and ancillary data inside MPLS packets. There has been significant recent interest in extending the MPLS data plane to carry such ancillary data to address a number of use cases described in this document. The use cases described 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.

This document describes important cases that require carrying additional ancillary data within the MPLS packets, as well as the means to indicate ancillary data is present. These use cases have been identified by the MPLS working group design team working on defining MPLS function Indicators and Ancillary Data (MIAD) for the MPLS data plane. The MPLS ancillary data can be classified as: implicit, or “no-data” associated with a funciton indicator, within the label stack, e.g., encoded as labels, referred to as In Stack Data (ISD), and after the Bottom of Stack (BoS), 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. ID: describes the applicability of IOAM to MPLS data plane. describes the network programming use case for SRv6 dataplane. 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. Some limitations of this approach that may be addressed by MIAD are described in .

The following terminology is used in the document: 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 . controller that is used to realize an IETF network slice . the collection of resources that are used to support a slice aggregate. Networks that transport time sensitive traffic.

ISD: In-stack data PSD: Post-stack data MIAD: MPLS Indicators and Ancillary Data

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 Operations, Administration, and Maintenance (IOAM) may record operational and telemetry information within the packet while the packet 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 End-to-End (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 use-cases of OAM and PM. 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 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. The presence of IOAM data will be transparent to nodes that does not support or do not participate in the IOAM process.

specifies the definition of an IETF Network Slice. It further discusses the general framework for requesting and operating IETF Network Slices, their characteristics, and the necessary system components and interfaces. Multiple network slices can be realized on top of a single shared network. In order to overcome scale challenges, IETF Network Slices may be aggregated into groups according to similar characteristics. The slice aggregate is a construct that comprises of the traffic flows of one or more IETF Network Slices of similar characteristics. A router that requires forwarding of a packet that belongs to a slice 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. The routers in the network that forward traffic over links that are shared by multiple slice aggregates need to identify the slice aggregate packets in order to enforce the associated forwarding action and treatment. An IETF network slice MAY support the following key features: A Slice Selector A Network Resource Partition associated with a slice aggregate. A Path selection criteria Verification that per slice SLOs are being met. This may be done by active measurements (inferred) or by using hybrid measurement methods, e.g., IOAM. Additionally, there is an on-going discussion on using Service Functions (SFs) with network slices. This may require insertion of an NSH. For multi-domain scenarios, a packet that traverses multiple domains may encode different identifiers within each domain.

A Global Identifier as a Flow-Aggregate Selector (FAS) can be encoded in the MPLS packet as defined in , , and . The FAS is used to associate the packets with a flow aggregate that utilizes resources defined by Network Resource Partition (NRP) as described in . The FAS can be encoded within an MPLS label carried in the packet’s MPLS label stack. All packets that belong to the same flow aggregate MAY carry the same FAS in the MPLS label stack. LSRs use the MPLS forwarding label to determine the forwarding next-hop(s), and can use the FAS present in the MPLS packet to infer the specific forwarding treatment that needs to be applied on the packet.

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. A similar approach is described in and .

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). 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 low end-to-end latency but does not influence the queueing of individual packets in each router along that path. TSN is required for networks transporting such time sensitive traffic, whose packets are required to be delivered to their final destination by a given time.

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 sensitive 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 or after BoS).

A number of different time formats commonly used in networking applications and can be used to encode the local deadlines. For the forwarding sub-entry we could adopt like SR-MPLS standard 32-bit MPLS labels (which contain a 20-bit label and BoS bit), and thus SR-TSN stack entries could be 64-bits in size comprising a 32-bit MPLS label and the aforementioned nonstandard 32-bit timestamp. Alternatively, an SR-TSN stack entry could be 96 bits in length comprising a 32-bit MPLS label and either of the standardized 64-bit timestamps.

describes how Service Function Chaining (SFC) can be realized in an MPLS network by emulating the NSH by using only MPLS label stack elements. A reference to the NSH SFC use case is defined in . The approach in introduces some limitations that are discussed in . This approach, however, can benefit from the solution framework introduced with MIAD. For example, it may be possible for the Network Service Header (NSH) to be embedded in an Extended Header (EH) to support the Path ID and any metadata that needs to be carried and and exchanged between Service Function Forwarders (SFFs).

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 .

Application-aware Networking (APN) as described in allows application-aware information (i.e., APN attributes) including APN identification (ID) and/or APN parameters (e.g. network performance requirements) to be encapsulated at network edge devices and carried in packets traversing an APN domain. The APN data is carried in packets to facilitate service provisioning, perform fine-granularity traffic steering and network resource adjustment. To support APN in MPLS networks, mechanisms are needed to carry such APN data in MPLS encapsulated packets.

Two or more of the aforementioned use cases MAY co-exist in the same packet. Some examples of such use cases are described below.

IOAM may provide key functions with network slicing to help ensure that critical network slice SLOs are being met by the network provider. In such a case, IOAM is able to collect key performance measurement parameters of network slice traffic flows as it traverses the transport network. This may require, in addition to carrying a specific network slice selector (e.g., GISS), the MPLS network slice packets may have to also carry IOAM ancillary data. Note that the IOAM ancillary data may have to be modified, and updated on some/all LSRs traversed by the network slice MPLS packets.

IOAM operation may also be desirable on MPLS packets that carry time-sensitive related data. Similarly, 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.

This document has no IANA actions.

This document introduces no new security considerations.

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

The following individuals contributed to this document:

Cisco Systems, Inc. Cisco Systems, Inc. Cisco Systems, Inc. Comcast Orange Comcast 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 new Generic Associated Channel (G-ACh) and updates the RFC 5586. 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 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 Corporation ZTE Corporation 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 handiling TTL expiration. The document also describes the processing of the G-ACh by the elements of the SFP. 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) records operational and telemetry information in the packet while the packet traverses a path in the network. This document discusses the data fields and associated data types for in-situ OAM. In-situ OAM data fields can be encapsulated into a variety of protocols such as NSH, Segment Routing, Geneve, or IPv6. In-situ OAM 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). Juniper Networks Juniper Networks Huawei Technologies Comcast Ericsson Ericsson ZTE Corporation ZTE Corporation Volta Networks Telefonica Nokia Verizon Network slicing provides 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. Network slices need to co-exist on the same network while ensuring slice elasticity in terms of network resource allocation. The Differentiated Service (Diffserv) model allows for carrying multiple services on top of a single physical network by relying on compliant domains and nodes to provide forwarding treatment (scheduling and drop policy) on to packets that carry the respective Diffserv code point. This document adopts a similar approach to Diffserv and proposes a scalable approach to realize network slicing in IP/MPLS networks. The solution does not mandate Diffserv to be enabled in the network to provide a specific forwarding treatment, but can co-exist with and complement it when enabled. 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 associated data, some in the label stack and some after the label stack. This proposal also solves the problem of scarcity of base SPLs. This approach can immediately address several use cases: * to carry a Slice 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 network infrastructure. 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. 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 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 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 also extends 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 specifies the architecture for Multiprotocol Label Switching (MPLS). [STANDARDS-TRACK] Huawei Technologies Futurewei Technologies KDDI Corporation China Telecom China Mobile China Mobile Cisco Systems This document describes the mechanism to associate network resource attributes to Segment Routing Identifiers (SIDs). Such SIDs are referred to as resource-aware SIDs in this document. The resource- aware SIDs retain their original forwarding semantics, but with the additional semantics to identify the set of network resources available for the packet processing and forwarding action. The resource-aware SIDs can therefore be used to build SR paths or virtual networks with a set of reserved network resources. The proposed mechanism is applicable to both segment routing with MPLS data plane (SR-MPLS) and segment routing with IPv6 data plane (SRv6). This document describes how to use a Service Function Forwarder (SFF) Label (similar to a pseudowire label or VPN label) to indicate the presence of a Service Function Chaining (SFC) Network Service Header (NSH) between an MPLS label stack and the packet original packet/ frame. This allows SFC packets using the NSH to be forwarded between SFFs over an MPLS network, and to select one of multiple SFFs in the destination MPLS node. Huawei Technologies Huawei Technologies Bell Canada China Telecom China Mobile China Unicom Verizon Inc. Network operators are facing the challenge of providing better network services for users. As the ever-developing 5G and industrial verticals evolve, more and more services that have diverse network requirements such as ultra-low latency and high reliability are emerging, and therefore differentiated service treatment is desired by users. On the other hand, as network technologies such as Hierarchical QoS (H-QoS), SR Policy, and Network Slicing keep evolving, the network has the capability to provide more fine- granularity differentiated services. However, network operators are typically unware of the applications that are traversing their network infrastructure, which means that not very effective differentiated service treatment can be provided to the traffic flows. As network technologies evolve including deployments of IPv6, SRv6, Segment Routing over MPLS dataplane, the programmability provided by IPv6 and Segment Routing can be augmented by conveying application related information into the network satifying the fine- granularity requirements. This document analyzes the existing problems caused by lack of service awareness, and outlines various use cases that could benefit from an Application-aware Networking (APN) framework.