



Internet Engineering Task Force (IETF)                           J. Haas
Request for Comments: 9384                              Juniper Networks
Category: Standards Track                                     March 2023
ISSN: 2070-1721


A BGP Cease NOTIFICATION Subcode for Bidirectional Forwarding Detection
                                 (BFD)

Abstract

   The Bidirectional Forwarding Detection (BFD) protocol (RFC 5880) is
   used to detect loss of connectivity between two forwarding engines,
   typically with low latency.  BFD is leveraged by routing protocols,
   including the Border Gateway Protocol (BGP), to bring down routing
   protocol connections more quickly than the original protocol timers.

   This document defines a subcode for the BGP Cease NOTIFICATION
   message (Section 6.7 of RFC 4271) for use when a BGP connection is
   being closed due to a BFD session going down.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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
   https://www.rfc-editor.org/info/rfc9384.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Requirements Language
   3.  BFD Cease NOTIFICATION Subcode
   4.  Operational Considerations
   5.  Security Considerations
   6.  IANA Considerations
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Acknowledgments
   Author's Address

1.  Introduction

   The Bidirectional Forwarding Detection (BFD) protocol [RFC5880] is
   used to detect loss of connectivity between two forwarding engines,
   typically with low latency.  BFD is utilized as a service for various
   clients, including routing protocols, to provide an advisory
   mechanism for those clients to take appropriate actions when a BFD
   session goes down [RFC5882].  This is typically used by the clients
   to trigger closure of their connections more quickly than the
   original protocol timers might allow.

   Border Gateway Protocol version 4 (BGP-4) [RFC4271] terminates its
   connections upon Hold Timer expiration when the speaker does not
   receive a BGP message within the negotiated Hold Time interval.  As
   per Sections 4.2 and 4.4 of [RFC4271], the minimum Hold Time interval
   is at least three seconds, unless KEEPALIVE processing has been
   disabled by negotiating the distinguished Hold Time of zero.

   If a BGP speaker desires to have its connections terminate more
   quickly than the negotiated BGP Hold Timer can accommodate upon loss
   of connectivity with a neighbor, the BFD protocol can be relied upon
   by BGP speakers to supply that faster detection.  When the BFD
   session state changes to Down, the BGP speaker terminates the
   connection with a Cease NOTIFICATION message sent to the neighbor, if
   possible, and then closes the TCP connection for the session.

   This document defines a subcode, "BFD Down", to be sent with the
   Cease NOTIFICATION message that indicates the reason for this type of
   connection termination.

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.  BFD Cease NOTIFICATION Subcode

   The value 10 has been allocated by IANA for the "BFD Down" Cease
   NOTIFICATION message subcode.

   When a BGP connection is terminated due to a BFD session going into
   the Down state, the BGP speaker SHOULD send a NOTIFICATION message
   with the error code "Cease" and the error subcode "BFD Down".

4.  Operational Considerations

   A BFD session may go into the Down state when there is only a partial
   loss of connectivity between two BGP speakers.  Operators using BFD
   for their BGP connections make choices regarding what BFD timers are
   used based upon a variety of criteria -- for example, stability vs.
   fast failure.

   In the event of a BGP connection being terminated due to a "BFD Down"
   event from partial loss of connectivity as detected by BFD, the
   remote BGP speaker might be able to receive a BGP Cease NOTIFICATION
   message with the "BFD Down" subcode.  The receiving BGP speaker will
   then have an understanding that the connection is being terminated
   because of a BFD-detected issue and not an issue with the BGP
   speaker.

   When there is a total loss of connectivity between two BGP speakers,
   it may not have been possible for the Cease NOTIFICATION message to
   have been sent.  Even so, BGP speakers SHOULD provide this reason as
   part of their operational state.  Examples include bgpPeerLastError
   per the BGP MIB [RFC4273] and "last-error" per [BGP-YANG].

   When the procedures in [RFC8538] for sending a NOTIFICATION message
   with a "Cease" code and "Hard Reset" subcode are required, and the
   BGP connection is being terminated because BFD has gone into the Down
   state, the "BFD Down" subcode SHOULD be encapsulated in the Hard
   Reset's data portion of the NOTIFICATION message.

5.  Security Considerations

   Similar to [RFC4486], this document defines a subcode for the BGP
   Cease NOTIFICATION message that provides information to aid network
   operators in correlating network events and diagnosing BGP peering
   issues.  This subcode is purely informational and has no impact on
   the BGP Finite State Machine beyond that already documented by
   [RFC4271], Sections 6.6 and 6.7.

6.  IANA Considerations

   IANA has assigned the value 10 from the "BGP Cease NOTIFICATION
   message subcodes" registry (https://www.iana.org/assignments/bgp-
   parameters/), with the name "BFD Down" and a reference to this
   document.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <https://www.rfc-editor.org/info/rfc5880>.

   [RFC5882]  Katz, D. and D. Ward, "Generic Application of
              Bidirectional Forwarding Detection (BFD)", RFC 5882,
              DOI 10.17487/RFC5882, June 2010,
              <https://www.rfc-editor.org/info/rfc5882>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8538]  Patel, K., Fernando, R., Scudder, J., and J. Haas,
              "Notification Message Support for BGP Graceful Restart",
              RFC 8538, DOI 10.17487/RFC8538, March 2019,
              <https://www.rfc-editor.org/info/rfc8538>.

7.2.  Informative References

   [BGP-YANG] Jethanandani, M., Patel, K., Hares, S., and J. Haas, "YANG
              Model for Border Gateway Protocol (BGP-4)", Work in
              Progress, Internet-Draft, draft-ietf-idr-bgp-model-16, 1
              March 2023, <https://datatracker.ietf.org/doc/html/draft-
              ietf-idr-bgp-model-16>.

   [RFC4273]  Haas, J., Ed. and S. Hares, Ed., "Definitions of Managed
              Objects for BGP-4", RFC 4273, DOI 10.17487/RFC4273,
              January 2006, <https://www.rfc-editor.org/info/rfc4273>.

   [RFC4486]  Chen, E. and V. Gillet, "Subcodes for BGP Cease
              Notification Message", RFC 4486, DOI 10.17487/RFC4486,
              April 2006, <https://www.rfc-editor.org/info/rfc4486>.

Acknowledgments

   Thanks to Jeff Tantsura and Dale Carder for their comments on this
   document.

   Mohamed Boucadair provided feedback as part of the Routing
   Directorate review of this document.

   In 2006, Bruno Rijsman had written a proposal that was substantively
   similar to this document: draft-rijsman-bfd-down-subcode.  That draft
   did not progress in the Inter-Domain Routing (IDR) Working Group at
   that time.  The author of this document was unaware of Bruno's prior
   work when creating this proposal.

Author's Address

   Jeffrey Haas
   Juniper Networks
   Email: jhaas@juniper.net
