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OPS OPSAWG control plane migration traffic monitoring traffic accounting OSPF IS-IS BGP Prefix-SID PCE PCEP SR This document introduces new IP Flow Information Export (IPFIX) code points to identify which traffic is being forwarded based on which MPLS control plane protocol is used within a Segment Routing domain. In particular, this document defines five code points for the IPFIX mplsTopLabelType Information Element for Path Computation Element (PCE), IS-IS, OSPFv2, OSPFv3, and BGP MPLS Segment Routing extensions.

Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are candidates for any level of Internet Standard; see Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .

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Table of Contents

• .  Introduction
• .  MPLS Segment Routing Top Label Type
• .  IANA Considerations
• .  Operational Considerations
• .  Security Considerations
• .  References
  • .  Normative References
  • .  Informative References
• Acknowledgements
• Author's Address

Introduction Four routing protocol extensions -- OSPFv2 Extensions, OSPFv3 Extensions, IS-IS Extensions, and BGP Prefix Segment Identifiers (Prefix-SIDs) -- and one Path Computation Element Communication Protocol (PCEP) Extension have been defined to be able to propagate Segment Routing (SR) labels for the MPLS data plane . Also, describes how IP Flow Information Export (IPFIX) can be leveraged in dimensional data modeling to account for traffic to MPLS SR label dimensions within a Segment Routing domain. In , the Information Element (IE) mplsTopLabelType(46) identifies which MPLS control plane protocol allocated the top-of-stack label in the MPLS label stack. Per , the "IPFIX MPLS label type (Value 46)" subregistry was created, where new MPLS label type entries should be added. This document defines new code points to address typical use cases that are discussed in .

MPLS Segment Routing Top Label Type By introducing five new code points to the IPFIX IE mplsTopLabelType(46) for Path Computation Element (PCE), IS-IS, OSPFv2, OSPFv3, and BGP Prefix-SIDs, it is possible to identify which traffic is being forwarded based upon which MPLS SR control plane protocol is in use. A typical use case is to monitor MPLS control plane migrations from LDP to IS-IS or OSPF Segment Routing. Such a migration can be done node by node as described in . Another use case is to monitor MPLS control plane migrations from dynamic BGP labels to BGP Prefix-SIDs . For example, the motivation for, and benefits of, such a migration in large-scale data centers are described in . Both use cases can be verified by using mplsTopLabelType(46), mplsTopLabelIPv4Address(47), mplsTopLabelIPv6Address(140), mplsTopLabelStackSection(70), and forwardingStatus(89) IEs to infer

• how many packets are forwarded or dropped
• if packets are dropped, for which reasons, and
• the MPLS provider edge loopback address and label protocol

By looking at the MPLS label value itself, it is not always clear to which label protocol it belongs. This is because they may share the same label allocation range. This is, for example, the case for IGP-Adjacency SIDs, LDP, and dynamic BGP labels.

IANA Considerations IANA has allocated the following code points in the "IPFIX MPLS label type (Value 46)" subregistry within the "IPFIX Information Elements" registry . See . Updates to "IPFIX MPLS label type (Value 46)" Subregistry

Value	Description	Reference
6	Path Computation Element	RFC 9160, RFC 8664
7	OSPFv2 Segment Routing	RFC 9160, RFC 8665
8	OSPFv3 Segment Routing	RFC 9160, RFC 8666
9	IS-IS Segment Routing	RFC 9160, RFC 8667
10	BGP Segment Routing Prefix-SID	RFC 9160, RFC 8669

References to RFCs 4364, 4271, and 5036 have been added to the "Reference" column in the "IPFIX MPLS label type (Value 46)" subregistry [IANA-IPFIX] for code points 3, 4, and 5, respectively. Previously, these references appeared in the "Additional Information" column for mplsTopLabelType(46) in the "IPFIX Information Elements" registry .

Operational Considerations In the IE mplsTopLabelType(46), BGP code point 4 refers to the label value in the MP_REACH_NLRI path attribute described in , while BGP Segment Routing Prefix-SID code point 10 corresponds to the label index value in the Label-Index TLV described in . These values are thus used for those distinct purposes.

Security Considerations There exist no significant extra security considerations regarding the allocation of these new IPFIX IEs as compared to .

References Normative References This document defines the data types and management policy for the information model for the IP Flow Information Export (IPFIX) protocol. This information model is maintained as the IANA "IPFIX Information Elements" registry, the initial contents of which were defined by RFC 5102. This information model is used by the IPFIX protocol for encoding measured traffic information and information related to the traffic Observation Point, the traffic Metering Process, and the Exporting Process. Although this model was developed for the IPFIX protocol, it is defined in an open way that allows it to be easily used in other protocols, interfaces, and applications. This document obsoletes RFC 5102. Informative References IANA This document specifies a set of procedures for using BGP to advertise that a specified router has bound a specified MPLS label (or a specified sequence of MPLS labels organized as a contiguous part of a label stack) to a specified address prefix. This can be done by sending a BGP UPDATE message whose Network Layer Reachability Information field contains both the prefix and the MPLS label(s) and whose Next Hop field identifies the node at which said prefix is bound to said label(s). This document obsoletes RFC 3107. Segment Routing (SR) leverages the source-routing paradigm. A node steers a packet through a controlled set of instructions, called segments, by prepending the packet with an SR header. In the MPLS data plane, the SR header is instantiated through a label stack. This document specifies the forwarding behavior to allow instantiating SR over the MPLS data plane (SR-MPLS). A Segment Routing (SR) node steers a packet through a controlled set of instructions, called segments, by prepending the packet with an SR header. A segment can represent any instruction, topological or service based. SR allows enforcing a flow through any topological path while maintaining per-flow state only at the ingress node to the SR domain. The Segment Routing architecture can be directly applied to the MPLS data plane with no change in the forwarding plane. This document describes how Segment Routing MPLS operates in a network where LDP is deployed and in the case where SR-capable and non-SR-capable nodes coexist. Segment Routing (SR) enables any head-end node to select any path without relying on a hop-by-hop signaling technique (e.g., LDP or RSVP-TE). It depends only on "segments" that are advertised by link-state Interior Gateway Protocols (IGPs). An SR path can be derived from a variety of mechanisms, including an IGP Shortest Path Tree (SPT), an explicit configuration, or a Path Computation Element (PCE). This document specifies extensions to the Path Computation Element Communication Protocol (PCEP) that allow a stateful PCE to compute and initiate Traffic-Engineering (TE) paths, as well as a Path Computation Client (PCC) to request a path subject to certain constraints and optimization criteria in SR networks. This document updates RFC 8408. Segment Routing (SR) allows a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological subpaths called "segments". These segments are advertised by the link-state routing protocols (IS-IS and OSPF). This document describes the OSPFv2 extensions required for Segment Routing. Segment Routing (SR) allows a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological subpaths called "segments". These segments are advertised by the link-state routing protocols (IS-IS and OSPF). This document describes the OSPFv3 extensions required for Segment Routing with the MPLS data plane. Segment Routing (SR) allows for a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological sub-paths, called "segments". These segments are advertised by the link-state routing protocols (IS-IS and OSPF). This document describes the IS-IS extensions that need to be introduced for Segment Routing operating on an MPLS data plane. Segment Routing (SR) leverages the source-routing paradigm. A node steers a packet through an ordered list of instructions called "segments". A segment can represent any instruction, topological or service based. The ingress node prepends an SR header to a packet containing a set of segment identifiers (SIDs). Each SID represents a topological or service-based instruction. Per-flow state is maintained only on the ingress node of the SR domain. An "SR domain" is defined as a single administrative domain for global SID assignment. This document defines an optional, transitive BGP attribute for announcing information about BGP Prefix Segment Identifiers (BGP Prefix-SIDs) and the specification for SR-MPLS SIDs. This document describes the motivation for, and benefits of, applying Segment Routing (SR) in BGP-based large-scale data centers. It describes the design to deploy SR in those data centers for both the MPLS and IPv6 data planes. Work in Progress

Acknowledgements I would like to thank the IE doctors, and , as well as , , , , , , , , , , , , , , and for their review and valuable comments. Many thanks also to for the AD review. Thanks to , , and for the IESG review.

Author's Address Swisscom

Binzring 17 Zürich 8045 Switzerland thomas.graf@swisscom.com