



Inter-Domain Routing                                             J. Haas
Internet-Draft                                          Juniper Networks
Intended status: Standards Track                        27 December 2022
Expires: 30 June 2023


A BGP Cease Notification Subcode For Bidirectional Forwarding Detection
                                 (BFD)
                     draft-ietf-idr-bfd-subcode-05

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 faster than the native protocol timers.

   This document defines a Subcode for the BGP Cease NOTIFICATION
   message [RFC4271], Section 6.7, for when a BGP connection is being
   closed due to a BFD session going down.

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.

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 30 June 2023.





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Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

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

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 native
   protocol timers might allow.

   The Border Gateway Protocol, Version 4 (BGP) [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 Section 4.2 and Section 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



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   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.  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".

3.  Operational Considerations

   A BFD session may go Down when there is only a partial loss of
   connectivity between two BGP speakers.  Operators using BFD for their
   BGP connections make choices for 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
   in the BGP MIB [RFC4273], and "last-error" in
   [I-D.ietf-idr-bgp-model].

   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 Down, the BFD
   Down Subcode SHOULD be encapsulated in the Hard Reset's data portion
   of the NOTIFICATION message.






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4.  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], Section 6.7.

5.  IANA Considerations

   NOTE TO IANA and the RFC Editor: IANA is requested to make the
   temporary allocation below permanent.  The RFC Editor is requested to
   delete this note to IANA prior to publication.

   IANA has assigned the value 10 from the BGP Cease NOTIFICATION
   message subcodes registry (https://www.iana.org/assignments/bgp-
   parameters/bgp-parameters.xhtml#bgp-parameters-8) with the Name "BFD
   Down", and a Reference to this document.

6.  Acknowledgments

   Thanks to Jeff Tantsura, and Dale Carder for their comments on the
   draft.

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

   Bruno Rijsman had a substantively similar proposal to this document
   in 2006; draft-rijsman-bfd-down-subcode.  That draft did not progress
   in IDR at that time.  The author of this draft was unaware of Bruno's
   prior work when creating this proposal.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S. and RFC Publisher, "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., Hares, S., Ed., and RFC
              Publisher, "A Border Gateway Protocol 4 (BGP-4)",
              RFC 4271, DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.





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

   [RFC5882]  Katz, D., Ward, D., and RFC Publisher, "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. and RFC Publisher, "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., Haas, J., and RFC
              Publisher, "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

   [I-D.ietf-idr-bgp-model]
              Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP
              YANG Model for Service Provider Networks", Work in
              Progress, Internet-Draft, draft-ietf-idr-bgp-model-15, 13
              October 2022, <https://www.ietf.org/archive/id/draft-ietf-
              idr-bgp-model-15.txt>.

   [RFC4273]  Haas, J., Ed., Hares, S., Ed., and RFC Publisher,
              "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., Gillet, V., and RFC Publisher, "Subcodes for BGP
              Cease Notification Message", RFC 4486,
              DOI 10.17487/RFC4486, April 2006,
              <https://www.rfc-editor.org/info/rfc4486>.

Author's Address

   Jeffrey Haas
   Juniper Networks
   Email: jhaas@juniper.net







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