IDR Workgroup                                                   M. Zheng
Internet-Draft                                    Individual Contributor
Intended status: Standards Track                               A. Lindem
Expires: May 5, 2020                                       Cisco Systems
                                                                 J. Haas
                                                  Juniper Networks, Inc.
                                                                   A. Fu
                                                          Bloomberg L.P.
                                                        November 2, 2019

                          BGP BFD Strict-Mode


   This document specifies extensions to RFC4271 BGP-4 that enable a BGP
   speaker to negotiate additional Bidirectional Forwarding Detection
   (BFD) extensions using a BGP capability.  This BFD capability enables
   a BGP speaker to prevent a BGP session from being established until a
   BFD session is established.  It is referred to as BGP BFD "strict-
   mode".  BGP BFD strict-mode will be supported when both the local
   speaker and its remote peer are BFD strict-mode capable.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 5, 2020.

Copyright Notice

   Copyright (c) 2019 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

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   ( 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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  BFD Strict-Mode Capability  . . . . . . . . . . . . . . . . .   3
   4.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Manageability Considerations  . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   8.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   4
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   Bidirectional Forwarding Detection BFD [RFC5882] enables routers to
   monitor data plane connectivity and to detect faults in the
   bidirectional forwarding path between them.  This capability is
   leveraged by routing protocols such as BGP [RFC4271] to rapidly react
   to topology changes in the face of path failures.

   The BFD interaction with BGP is specified in Section 10.2 of
   [RFC5882].  When BFD is enabled for a BGP neighbor, faults in the
   bidirectional forwarding detected by BFD result in session
   termination.  It is possible in some failure scenarios for the
   network to be in a state such that a BGP session may be established
   but a BFD session cannot be established.  In some other scenarios, it
   may be possible to establish a BGP session, but a degraded or poor-
   quality link may result in the corresponding BFD session going up and
   down frequently.

   To avoid situations which result in routing churn and to minimize the
   impact of network interruptions, it will be beneficial to disallow
   BGP to establish a session until BFD session is successfully
   established and has stabilized.  We refer to this mode of operation
   as BGP BFD "strict-mode".  However, always using "strict-mode" would
   preclude BGP operation in an environment where not all routers
   support BFD strict-mode or have BFD enabled.  This document defines
   BGP "strict-mode" operation as preventing BGP session establishment
   until both the local and remove speakers have a stable BFD session.

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   The document also specifies the BGP protocol extensions for BGP
   capability [RFC5492] for announcing BFD parameters including a BGP
   speaker's support for "strict-mode", i.e., requiring a BFD session
   for BGP session establishment.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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 Strict-Mode Capability

   The BGP Strict-Mode Capability [RFC5492] will allow a BGP speaker's
   to advertise this capability.  The capability is defined as follows:

   Capability code: TBD

   Capability length: 0 octets

4.  Operation

   A BGP speaker which supports capabilities advertisement MUST include
   the BFD strict-mode capability.

   A BGP speaker which supports the BFD Strict-Mode capability, examines
   the list of capabilities present in the capabilities that the speaker
   receives from its peer.  If both the local and remote BGP speakers
   include the BFD strict-mode capability, the BGP finite state machine
   does not transition to the Established state from OpenSent or
   OpenConfirm state [RFC4271] until the BFD session is in the Up state
   (see below for AdminDown state).  This means that a KEEPALIVE message
   is not sent nor is the KeepaliveTimer set.

   If the BFD session does not transition to the Up state, and the
   HoldTimer has been negotiated to a non-zero value, the BGP FSM will
   close the session appropriately.  If the HoldTimer has been
   negotiated to a zero value, the session should be closed after a time
   of X.  This time X is referred as "BGP BFD Hold time".  The proposed
   default BGP BFD Hold time value is 30 seconds.  The BGP BFD Hold time
   value is configurable.

   If BFD session is in the AdminDown state, then the BGP finite state
   machine will proceed normally without input from BFD.  This means
   that BFD session "AdminDown" state WILL NOT prevent the BGP state
   transition to Established state from OpenConfirm.

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   Once the BFD session has transitioned to the Up state, the BGP FSM
   may proceed to transition to the Established state from the OpenSent
   or OpenConfirm state appropriately.  I.e. a KEEPALIVE message is
   sent, and the KeepaliveTimer is started.

   If either BGP peer has not advertised the BFD Strict-Mode Capability,
   then a BFD session WILL NOT be required for the BGP session to reach
   Established state.  This does not preclude usage of BFD after BGP
   session establishment [RFC5882].

5.  Manageability Considerations

   Auto-configuration is possible for the enabling BGP BFD Strict-Mode.
   However, the configuration automation is out of the scope of this

   A BGP NOTIFICATION message Subcode indicating BFD Hold timer
   expiration may be required for network management.  (To be discussed
   in the next revision of this document.)

6.  Security Considerations

   The mechanism defined in this document interacts with the BGP finite
   state machine when so configured.  The security considerations of BFD
   thus, become considerations for BGP-4 [RFC4271] so used.  Given that
   a BFD session is required for a BGP session, a Denial-of-Service
   (DoS) attack on BGP can now be mounted by preventing a BFD session
   between the BGP peers from being established or interrupting an
   existing BFD session.  The use of the BFD Authentication mechanism
   defined in [RFC5880] is thus RECOMMENDED when used to protect BGP-4

7.  IANA Considerations

   This document defines a new BGP capability - BFD Capability.  The
   Capability Code for BFD Capability is TBD.

8.  Acknowledgement

   The authors would like to acknowledge the review and inputs from
   Shyam Sethuram, Mohammed Mirza, Bruno Decraene, Carlos Pignataro, and
   Enke Chen.

9.  Normative References

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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [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,

   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
              2009, <>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,

   [RFC5882]  Katz, D. and D. Ward, "Generic Application of
              Bidirectional Forwarding Detection (BFD)", RFC 5882,
              DOI 10.17487/RFC5882, June 2010,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

Authors' Addresses

   Mercia Zheng
   Individual Contributor


   Acee Lindem
   Cisco Systems
   301 Midenhall Way
   GARY, NC 27513


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Internet-Draft             BGP BFD Strict-Mode             November 2019

   Jeffrey Haas
   Juniper Networks, Inc.
   1133 Innovation Way


   Albert Fu
   Bloomberg L.P.


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