1.1.Terminology

The following terminology is used in the document:¶

RFC 9543 Network Slice

is interpreted as defined in[RFC9543].Furthermore, in this document, the term "network slice" is used interchangeably as a shorter versionof RFC 9543 Network Slice term.¶

The MPLS Ancillary Data (AD) classified as:

• residing within the MPLS label stack and referred to as In Stack Data (ISD), and¶

• residing after the Bottom of Stack (BoS) and referred to as Post Stack Data (PSD).¶

2.1.No Further Fastreroute

MPLS Fast Reroute[RFC4090],[RFC5286] and[RFC7490] is a usefuland widely deployed tool for minimizing packet loss in the case of a link ornode failure.¶

Several cases exist where, once a Fast Reroute (FRR) has taken place in an MPLS network andresulted in rerouting a packet away from the failure, a second FRR impactsthe same packet on another node, and may result in traffic disruption.¶

In such a case, the packet impacted by multiple FRR events may continue to loopbetween the label switch routers (LSRs) that activated FRR until the packet's TTLexpires. This can lead to link congestion and further packet loss. To avoid that situation, packets that have been redirected by FRR will be marked using MNA to preclude further FRR processing.¶

2.2.Applicability of Hybrid Measurement Methods

MNA can be used to carry information essential for collecting operational informationand measuring various performance metrics that reflect the experience of the packet marked by MNA.Optionally, the operational state and telemetry information collected onthe LSR may be transported using MNA techniques.¶

2.3.Network Slicing

An RFC 9543 Network Slice service ([RFC9543])provides connectivity coupled with a set ofnetwork resource commitments and is expressed in terms of one or moreconnectivity constructs.[RFC9543] also defines a Network Resource Partition (NRP) Policyas a policy construct that enables the instantiation of mechanisms to support one or more network slice services.The packets associated with an NRP may carry amarking in their network layer header to identify this association,which is referred to as an NRP Selector. The NRP Selector is usedto map a packet to the associated set of network resources and provide thecorresponding forwarding treatment onto the packet.¶

A router that requires the forwarding of a packet that belongs to an NRPmay have to decide on the forwarding action to take based on selectednext-hop(s), and the forwarding treatment (e.g., scheduling and drop policy) toenforce based on the associated per-hop behavior.¶

In this case, routers that forward traffic over a physical link shared by multipleNRPs need to identify the NRP to which the packet belongs to enforce their respective forwarding actions and treatments.¶

MNA technologies can be used to signal actions for MPLS packetsand carry data essential for these actions. For example, MNA can carry the NRP Selector[I-D.ietf-teas-ns-ip-mpls] in MPLS packets.¶

2.4.NSH-based Service Function Chaining

[RFC8595] describes how Service Function Chaining can be realized inan MPLS network by emulating the Network Service Header (NSH) using only MPLS label stack elements.¶

The approach in[RFC8595] introduces some limitations that are discussed in[I-D.lm-mpls-sfc-path-verification]. This approach, however, can benefitfrom the framework introduced with MNA in[I-D.ietf-mpls-mna-fwk].¶

MNA can be used to extend NSH emulation using MPLSlabels[RFC8595] to support the functionality of NSH Context Headers,whether fixed or variable-length. For example, MNA could support Flow ID[RFC9263] that may be used for load-balancing amongService Function Forwarders and/or the Service Functionswithin the same Service Function Path.¶

2.5.Network Programming

In Segment Routing (SR), an ingress node steers a packet through an ordered list of instructionscalled "segments". Each one of these instructions represents afunction to be called at a specific location in the network. Afunction is locally defined on the node where it is executed and mayrange from simply moving forward in the segment list to any complexuser-defined behavior.¶

Network Programming combines SR functions to achieve anetworking objective that goes beyond mere packet routing.¶

Encoding a pointer to a function and its arguments within an MPLS packet transport header may be desirable.MNA can be used to encode the FUNC::ARGs to support the functionalequivalent of FUNC::ARG in SRv6 as described in[RFC8986].¶

A.1.Generic Delivery Functions

The Generic Delivery Functions (GDFs), defined in[I-D.zzhang-intarea-generic-delivery-functions], provide a new mechanism tosupport functions analogous to those supported through the IPv6 ExtensionHeaders mechanism. For example, GDF can support fragmentation/reassemblyfunctionality in the MPLS network by using the Generic Fragmentation Header.MNA can support GDF by placing a GDF header in an MPLS packet within thePost-Stack Data block[I-D.ietf-mpls-mna-fwk]. Multiple GDF headers can alsobe present in the same MPLS packet organized as a list of headers.¶

A.2.Delay Budgets for Time-Bound Applications

The routers in a network can perform two distinct functions on incomingpackets, namely forwarding (where the packet should be sent) and scheduling(when the packet should be sent). IEEE-802.1 Time Sensitive Networking (TSN) andDeterministic Networking provide several mechanisms for scheduling under theassumption that routers are time-synchronized. The most effective mechanismsfor delay minimization involve per-flow resource allocation.¶

Segment Routing (SR) is a forwarding paradigm that allows encoding forwardinginstructions in the packet in a stack data structure rather than beingprogrammed into the routers. The SR instructions are contained within a packetin the form of a First-in First-out stack dictating the forwarding decisions ofsuccessive routers. Segment routing may be used to choose a path sufficientlyshort to be capable of providing a bounded end-to-end latency but doesnot 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 thedelivery of such packets that can be delivered to their final destination within agiven time budget. One approach to address this use case in SR-MPLS wasdescribed in[I-D.stein-srtsn].¶

A.3.Stack-Based Methods for Latency Control

One efficient data structure for inserting local deadlines intothe headers is a "stack", similar to that used in Segment Routing tocarry forwarding instructions. The number of deadline values in thestack equals the number of routers the packet needs to traverse inthe network, and each deadline value corresponds to a specificrouter. The Top-of-Stack (ToS) corresponds to the first router'sdeadline, while the MPLS BoS refers to the last. Alllocal deadlines in the stack are later or equal to the current time(upon which all routers agree), and times closer to the ToS arealways earlier or equal to times closer to the MPLS BoS.¶

The ingress router inserts the deadline stack into the packet headers; no otherrouter needs to be aware of the requirements of the time-bound flows.Hence, admitting a new flow only requires updating the information base of theingress router.¶

MPLS LSRs that expose the ToS label can also inspect theassociated "deadline" carried in the packet (either in the MPLS stack as ISD orafter BoS as PSD).¶