Internet-Draft Clarify Bootstrapping BFD over MPLS LSP March 2021
Mirsky, et al. Expires 1 October 2021 [Page]
Workgroup:
MPLS Working Group
Internet-Draft:
draft-mirsky-mpls-bfd-bootstrap-clarify-02
Updates:
5884 (if approved)
Published:
Intended Status:
Standards Track
Expires:
Authors:
G. Mirsky
ZTE Corporation
Y. Zhao
ZTE Corporation
G. Mishra
Verizon Inc.

Clarifying Use of LSP Ping to Bootstrap BFD over MPLS LSP

Abstract

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 https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 1 October 2021.

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 to be used for the Return mode field [RFC8029] when LSP ping is used to bootstrap a BFD session of MPLS LSP. When LSP echo request is being used to detect defects in MPLS data plane and verify consistency between the control plane and the data plane echo reply is needed to confirm the correct state, provide positive acknowledgment. But when an LSP echo request is being used to bootstrap BFD session, then the positive acknowledgment, according to [RFC5884] is provided by the egress transmitting BFD control message. Thus LSP echo reply is not required to bootstrap BFD session and hence the Return mode field in echo request message SHOULD be set to 1 (Do not reply) [RFC8029] when LSP echo request used to bootstrap BFD session.

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 echo reply to BFD bootstrapping echo request.

5. IANA Considerations

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

6. Security Considerations

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

7. Acknowledgements

TBA

8. Normative References

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC5880]
Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD)", RFC 5880, DOI 10.17487/RFC5880, , <https://www.rfc-editor.org/info/rfc5880>.
[RFC5884]
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, , <https://www.rfc-editor.org/info/rfc5884>.
[RFC8029]
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, , <https://www.rfc-editor.org/info/rfc8029>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.

Authors' Addresses

Greg Mirsky
ZTE Corporation
Yanhua Zhao
ZTE Corporation
Gyan Mishra
Verizon Inc.