Internet-Draft Clarify Bootstrapping BFD over MPLS LSP January 2024
Mirsky, et al. Expires 12 July 2024 [Page]
MPLS Working Group
5884 (if approved)
Intended Status:
Standards Track
G. Mirsky
Y. Zhao
ZTE Corporation
G. Mishra
Verizon Inc.
R. Bonica
Juniper Networks

Clarifying Use of LSP Ping to Bootstrap BFD over MPLS LSP


This document, if approved, updates RFC 5884 by clarifying procedures for using MPLS LSP ping to bootstrap Bidirectional Forwarding Detection (BFD) over MPLS Label Switch Path.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at

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This Internet-Draft will expire on 12 July 2024.

Table of Contents

1. Introduction

[RFC5884] defines how LSP Ping [RFC8029] uses BFD Discriminator TLV to bootstrap Bidirectional Forwarding Detection (BFD) session over MPLS Label Switch Path (LSP). Implementation and operational experiences suggest that two aspects of using LSP ping to bootstrap BFD session can benefit from clarification. This document updates [RFC5884] in use of Return Mode field in MPLS LSP echo request message and use of BFD Discriminator TLV in MPLS LSP echo reply.

2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. Use of Return Mode Field

[RFC5884] does not define the value for the Return Mode field [RFC8029] when LSP ping is used to bootstrap a BFD session of MPLS LSP. When an LSP echo request is used to detect defects in the MPLS data plane and verify consistency between the control plane and the data plane, an echo reply is needed to confirm the correct state and provide positive acknowledgment. But when an LSP echo request is used to bootstrap a BFD session, the positive acknowledgment, according to[RFC5884], is provided by the egress transmitting BFD control message. Thus LSP echo reply is not used to bootstrap the BFD session, and hence the Return Mode field in the echo request message SHOULD be set to 1 (Do not reply) [RFC8029] when LSP echo request is used to bootstrap a BFD session. If bootstrapping a BFD session is combined with the periodic verification of a FEC as described in [RFC8029], the Return Mode field MAY be set to 2 (Reply via an IPv4/IPv6 UDP packet). Furthermore, as proposed in [I-D.kompella-mpls-lspping-norao], the value of the Return Mode field in the echo request used to bootstrap a BFD session MUST NOT be set to 3 (Reply via an IPv4/IPv6 UDP packet with Router Alert).

4. Use of BFD Discriminator TLV in LSP Echo Reply

[RFC5884] in section 6 defines that echo reply by the egress LSR to BFD bootstrapping echo request MAY include BFD Discriminator TLV with locally assigned discriminator value for the BFD session. But the [RFC5884] does not define how the ingress LSR may use the returned value. From a practical point, as discussed in Section 3, the returned value is not useful since the egress is required to send the BFD control message right after successfully validating the FEC and before sending an echo reply message. Secondly, identifying the corresponding BFD session at ingress without returning its discriminator presents an unnecessary challenge for the implementation. Thus the egress LSR SHOULD NOT include BFD Discriminator TLV if sending an echo reply to BFD bootstrapping echo request.

5. Destination IPv6 Address

[RFC5884] requires that the IPv6 Destination Address used in IP/UDP encapsulation of an echo request packet is selected from the IPv4 loopback address range mapped to IPv6. Such packets do not have the same behavior as prescribed in [RFC1122] for an IPv4 loopback addressed packet.

[RFC4291] defines ::1/128 as the single IPv6 loopback address. Considering that this specification updates Section 7 of [RFC5884] regarding the selection of an IPv6 destination address for a BFD Control message:

6. IANA Considerations

This document does not require any action by IANA. This section may be removed.

7. Security Considerations

This document does not introduce new security aspects but inherits all security considerations from [RFC5880], [RFC5884], [RFC8029].

8. Acknowledgements


9. Normative References

Kompella, K., Bonica, R., and G. Mirsky, "Deprecating the Use of Router Alert in LSP Ping", Work in Progress, Internet-Draft, draft-kompella-mpls-lspping-norao-02, , <>.
Braden, R., Ed., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, DOI 10.17487/RFC1122, , <>.
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, , <>.
Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD)", RFC 5880, DOI 10.17487/RFC5880, , <>.
Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, "Bidirectional Forwarding Detection (BFD) for MPLS Label Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884, , <>.
Kompella, K., Drake, J., Amante, S., Henderickx, W., and L. Yong, "The Use of Entropy Labels in MPLS Forwarding", RFC 6790, DOI 10.17487/RFC6790, , <>.
Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N., Aldrin, S., and M. Chen, "Detecting Multiprotocol Label Switched (MPLS) Data-Plane Failures", RFC 8029, DOI 10.17487/RFC8029, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.

Authors' Addresses

Greg Mirsky
Yanhua Zhao
ZTE Corporation
Gyan Mishra
Verizon Inc.
Ron Bonica
Juniper Networks
1133 Innovation Way
Sunnyvale, CA 94089
United States