Export of MPLS Segment Routing Label Type Information in IP Flow Information Export (IPFIX)

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Table of Contents

1. Introduction

Four new routing protocol extensions, OSPFv2 Extensions [RFC8665], OSPFv3 Extensions [RFC8666], IS-IS Extensions [RFC8667] and BGP Prefix Segment Identifiers (Prefix-SIDs) [RFC8669] have been defined as routing protocols that are able to propagate Segment Routing (SR) labels for the MPLS data plane [RFC8660].¶

Also, [I-D.ali-spring-sr-traffic-accounting] describes how IP Flow Information Export [RFC7012] can be leveraged to account traffic to MPLS SR label dimensions within a Segment Routing domain.¶

In [RFC7012], the Information Element (IE) mplsTopLabelType(46) identifies which MPLS control plane protocol allocated the top-of-stack label in the MPLS label stack. Section 7.2 of [RFC7012] creates the "IPFIX MPLS label type (Value 46)" subregistry [IANA-IPFIX] where MPLS label type should be added. This document defines new code points to address typical use cases that are discussed in Section 2.¶

2. MPLS Segment Routing Top Label Type

By introducing four new code points to the IPFIX IE mplsTopLabelType(46) for IS-IS, OSPFv2, OSPFv3 and BGP Prefix-SID, 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 Appendix A of [RFC8661].¶

Another use case is to monitor MPLS control plane migrations from dynamic BGP labels [RFC8277] to BGP Prefix-SIDs in the context of Seamless MPLS SR described in Section 4.6 of [I-D.hegde-spring-mpls-seamless-sr].¶

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 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 as 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.¶

3. IANA Considerations

This document requests IANA to allocate the following code points in the existing subregistry "IPFIX MPLS label type (Value 46)" under the "IPFIX Information Elements" registry [RFC7012] available at [IANA-IPFIX].¶

      +-------+--------------------------------+----------------------+
      | Value |          Description           |      Reference       |
      +-------+--------------------------------+----------------------+
      | TBD1  | OSPFv2 Segment Routing         | [RFC-to-be], RFC8665 |
      +-------+--------------------------------+----------------------+
      | TBD2  | OSPFv3 Segment Routing         | [RFC-to-be], RFC8666 |
      +-------+--------------------------------+----------------------+
      | TBD3  | IS-IS Segment Routing          | [RFC-to-be], RFC8667 |
      +-------+--------------------------------+----------------------+
      | TBD4  | BGP Segment Routing Prefix-SID | [RFC-to-be], RFC8669 |
      +-------+--------------------------------+----------------------+

      Table 1: Updates to "IPFIX MPLS label type (Value 46)" subregistry

Note to the RFC-Editor:¶

• Please replace TBD1 - TBD4 with the values allocated by IANA¶
• Please replace the [RFC-to-be] with the RFC number assigned to this document¶

4. Operational Considerations

In the IE mplsTopLabelType(46), the BGP code point 4 refers to the label value in MP_REACH_NLRI path attribute described in Section 2 of [RFC8277], while the BGP Segment Routing Prefix-SID code point TBD4 corresponds to the label index value in the Label-Index TLV described in Section 3.1 of [RFC8669]. These values are thus used for those distinct purposes.¶

5. Security Considerations

There exists no extra security considerations regarding the allocation of these new IPFIX IEs compared to [RFC7012].¶

6. Acknowledgements

I would like to thank the IE doctors, Paul Aitken and Andrew Feren, as well Benoit Claise, Loa Andersson, Tianran Zhou, Pierre Francois, Bruno Decreane, Paolo Lucente, Hannes Gredler, Ketan Talaulikar, Sabrina Tanamal, Erik Auerswald, Sergey Fomin, Mohamed Boucadair, Tom Petch, Qin Wu and Matthias Arnold for their review and valuable comments. Many thanks also to Robert Wilton for the AD review.¶

Author's Address