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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.

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 Informative References IANA

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.