Skip to main content

Border Gateway Protocol 4 (BGP-4) Send Hold Timer
draft-ietf-idr-bgp-sendholdtimer-00

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 9687.
Expired & archived
Authors Job Snijders , Ben Cartwright-Cox
Last updated 2023-11-06 (Latest revision 2023-05-05)
Replaces draft-spaghetti-idr-bgp-sendholdtimer
RFC stream Internet Engineering Task Force (IETF)
Formats
Reviews
Additional resources Mailing list discussion
Stream WG state WG Document
Document shepherd Susan Hares
Shepherd write-up Show Last changed 2023-05-23
IESG IESG state Became RFC 9687 (Proposed Standard)
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD (None)
Send notices to shares@ndzh.com
draft-ietf-idr-bgp-sendholdtimer-00
IDR                                                          J. Snijders
Internet-Draft                                                    Fastly
Updates: 4271 (if approved)                            B. Cartwright-Cox
Intended status: Standards Track                            Port 179 Ltd
Expires: 6 November 2023                                      5 May 2023

           Border Gateway Protocol 4 (BGP-4) Send Hold Timer
                  draft-ietf-idr-bgp-sendholdtimer-00

Abstract

   This document defines the SendHoldTimer session attribute for the
   Border Gateway Protocol (BGP) Finite State Machine (FSM).
   Implementation of a SendHoldTimer should help overcome situations
   where BGP sessions are not terminated after it has become detectable
   for the local system that the remote system is not processing BGP
   messages.  For robustness, this document specifies that the local
   system should close BGP connections and not solely rely on the remote
   system for session closure when BGP timers have expired.  This
   document updates RFC4271.

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 6 November 2023.

Snijders & Cartwright-CoxExpires 6 November 2023                [Page 1]
Internet-Draft              BGP SendHoldTimer                   May 2023

Copyright Notice

   Copyright (c) 2023 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.  Example of a problematic scenario . . . . . . . . . . . . . .   3
   3.  Specification of the Send Hold Timer  . . . . . . . . . . . .   3
     3.1.  Session Attributes  . . . . . . . . . . . . . . . . . . .   3
     3.2.  SendHoldTimer_Expires Event Definition  . . . . . . . . .   4
     3.3.  MsgSent Event Definition  . . . . . . . . . . . . . . . .   5
     3.4.  Restarting the SendHoldTimer  . . . . . . . . . . . . . .   5
   4.  Send Hold Timer Expired Error Handling  . . . . . . . . . . .   5
   5.  Operational Considerations  . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Implementation status - RFC EDITOR: REMOVE BEFORE
           PUBLICATION . . . . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   This document defines the SendHoldTimer session attribute for the
   Border Gateway Protocol (BGP) [RFC4271] Finite State Machine (FSM)
   defined in section 8.

   Failure to terminate a 'stuck' BGP session can result in Denial Of
   Service, the subsequent failure to generate and deliver BGP WITHDRAW
   messages to other BGP peers of the local system is detrimental to all
   participants of the inter-domain routing system.  This phenomena is
   theorised to have contributed to IP traffic backholing events in
   global Internet routing system [bgpzombies].

Snijders & Cartwright-CoxExpires 6 November 2023                [Page 2]
Internet-Draft              BGP SendHoldTimer                   May 2023

   This specification intends to improve this situation by requiring
   sessions to be terminated if the local system has detected that the
   remote system cannot possibly have received any BGP messages for the
   duration of the SendHoldTimer.  Through codification of the
   aforementioned requirement, operators will benefit from consistent
   behavior across different BGP implementations.

   BGP speakers following this specification do not exclusively rely on
   remote systems robustly closing connections, but will also locally
   close connections.

2.  Example of a problematic scenario

   In implementations lacking the concept of a SendHoldTimer, a
   malfunctioning or overwhelmed remote peer may cause data on the BGP
   socket in the local system to accumulate ad infinitum.  This could
   result in forwarding failure and traffic loss, as the overwhelmed
   peer continues to utilize stale routes.

   An example fault state: as BGP runs over TCP [RFC9293] it is possible
   for hosts in the ESTABLISHED state to encounter a BGP peer that is
   advertising a TCP Receive Window (RCV.WND) of size zero, this 0
   window prevents the local system from sending KEEPALIVE, CEASE,
   WITHDRAW, UPDATE, or any other critical BGP messages across the
   network socket to the remote peer.  Historically, many BGP
   implementations were unable to handle this situation in a robust
   fashion.  Previous BGP RFC specifications would not give cause for
   the session to be torn down in such situations.

   Generally BGP implementation have no visibility into lower-layer
   subsystems such as TCP or the peer's current Receive Window.
   Therefore, this document relies upon BGP implementations having the
   ability to detect whether the TCP socket to a BGP peer is progressing
   (data is being transmitted), or persisting in a stalled state.

3.  Specification of the Send Hold Timer

   BGP speakers are implemented following a conceptual model "BGP Finite
   State Machine" (FSM), which is outlined in section 8 of [RFC4271].
   This specification updates the BGP FSM as following:

3.1.  Session Attributes

   The following mandatory session attributes are added to paragraph 6
   of Section 8, before "The state session attribute indicates the
   current state of the BGP FSM":

      9) SendHoldTimer

Snijders & Cartwright-CoxExpires 6 November 2023                [Page 3]
Internet-Draft              BGP SendHoldTimer                   May 2023

      10) SendHoldTime (an initial value of 8 minutes is recommended)

3.2.  SendHoldTimer_Expires Event Definition

   Section 8.1.3 [RFC4271] is extended as following:

       Event XX1: SendHoldTimer_Expires
       Definition : An event generated when the SendHoldTimer expires.
       Status: Mandatory

   If the SendHoldTimer_Expires (Event XX1), the local system:

      -  logs a message with the BGP Error Notification Code "Send Hold
         Timer Expired",

      -  releases all BGP resources,

      -  sets the ConnectRetryTimer to zero,

      -  drops the TCP connection,

      -  increments the ConnectRetryCounter,

      -  (optionally) performs peer oscillation damping if the
         DampPeerOscillations attribute is set to TRUE, and

      -  changes its state to Idle.

   If the DelayOpenTimer_Expires event (Event 12) occurs in the Connect
   state, the local system:

      -  sends an OPEN message to its peer,

      -  sets the HoldTimer to a large value, and

      -  sets the SendHoldTimer to a large value, and

      -  changes its state to OpenSent.

   If the DelayOpen attribute is set to FALSE, the local system:

      -  stops the ConnectRetryTimer (if running) and sets the
         ConnectRetryTimer to zero,

      -  completes BGP initialization

      -  sends an OPEN message to its peer,

Snijders & Cartwright-CoxExpires 6 November 2023                [Page 4]
Internet-Draft              BGP SendHoldTimer                   May 2023

      -  sets the HoldTimer to a large value, and

      -  sets the SendHoldTimer to a large value, and

      -  changes its state to OpenSent.

   A HoldTimer value of 4 minutes is suggested.

   A SendHoldTimer value of 8 minutes is suggested.

3.3.  MsgSent Event Definition

   Section 8.1.5 [RFC4271] is extended as following:

   Event XX2: MsgSent
   Definition: An event is generated when a KEEPALIVE or UPDATE message is transmitted.
   Status: Mandatory

3.4.  Restarting the SendHoldTimer

   On page 74 [RFC4271] before "If the local system receives an UPDATE
   message, and the UPDATE message error handling procedure (see
   Section 6.3) detects an error (Event 28), the local system:", add the
   following:

   If the local system transmits a KEEPALIVE or UPDATE message (MsgSent
   (Event XX2)), the local system:

      -  restarts the SendHoldTimer, and

      -  remains in the Established state.

4.  Send Hold Timer Expired Error Handling

   If a system does not send successive KEEPALIVE, UPDATE, and/or
   NOTIFICATION messages within the period specified in the Send Hold
   Time, then the BGP connection is closed and a log message is emitted.

5.  Operational Considerations

   When the local system recognizes a remote peer is not processing any
   BGP messages for the duration of the Send Hold Timer, the local
   system will not be able to inform the remote peer through a BGP
   message as to why the session is being closed (i.e. a NOTIFICATION
   message with the "Send Hold Timer Expired" error code).

   Even so, BGP speakers SHOULD provide this reason as part of their
   operational state; e.g. bgpPeerLastError in the BGP MIB [RFC4273].

Snijders & Cartwright-CoxExpires 6 November 2023                [Page 5]
Internet-Draft              BGP SendHoldTimer                   May 2023

6.  Security Considerations

   This specification addresses the vulnerability of a BGP speaker to a
   potential attack whereby a BGP peer can pretend to be unable to
   process BGP messages and in doing so create a scenario where the
   local system is poisoned with stale routing information.

   There are three detrimental aspects to the problem of not robustly
   handling 'stuck' peers:

   *  Failure to send BGP messages to a peer implies the peer is
      operating based on stale routing information.

   *  Failure to disconnect from a 'stuck' peer hinders the local
      system's ability to construct a non-stale local Routing
      Information Base (RIB).

   *  Failure to disconnect from a 'stuck' peer hinders the local
      system's ability to inform other BGP peers with current network
      reachability information.

   In other respects, this specification does not change BGP's security
   characteristics.

7.  IANA Considerations

   This document requests IANA to assign a value named "Send Hold Timer
   Expired" in the "BGP Error (Notification) Codes" sub-registry under
   the "Border Gateway Protocol (BGP) Parameters" registry.

8.  Acknowledgements

   The authors would like to thank William McCall, Theo de Raadt, John
   Heasley, Nick Hilliard, Jeffrey Haas, and Tom Petch for their helpful
   review of this document.

9.  References

9.1.  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>.

Snijders & Cartwright-CoxExpires 6 November 2023                [Page 6]
Internet-Draft              BGP SendHoldTimer                   May 2023

   [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>.

   [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>.

   [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>.

   [RFC9293]  Eddy, W., Ed., "Transmission Control Protocol (TCP)",
              RFC 9293, DOI 10.17487/RFC9293, August 2022,
              <https://www.rfc-editor.org/info/rfc9293>.

9.2.  Informative References

   [bgpzombies]
              Fontugne, R., "BGP Zombies", April 2019,
              <https://labs.ripe.net/author/romain_fontugne/bgp-
              zombies/>.

   [frr]      Lamparter, D., "bgpd: implement SendHoldTimer", May 2022,
              <https://github.com/FRRouting/frr/pull/11225>.

   [neo-bgp]  Cartwright-Cox, B., "What does bgp.tools support", August
              2022, <https://bgp.tools/kb/bgp-support>.

   [openbgpd] Jeker, C., "bgpd send side hold timer", December 2020,
              <https://marc.info/?l=openbsd-tech&m=160820754925261&w=2>.

Appendix A.  Implementation status - RFC EDITOR: REMOVE BEFORE
             PUBLICATION

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in RFC 7942.
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

Snijders & Cartwright-CoxExpires 6 November 2023                [Page 7]
Internet-Draft              BGP SendHoldTimer                   May 2023

   According to RFC 7942, "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

   *  OpenBGPD [openbgpd]

   *  FRRouting [frr]

   *  neo-bgp (bgp.tools) [neo-bgp]

Authors' Addresses

   Job Snijders
   Fastly
   Amsterdam
   Netherlands
   Email: job@fastly.com

   Ben Cartwright-Cox
   Port 179 Ltd
   London
   United Kingdom
   Email: ben@benjojo.co.uk

Snijders & Cartwright-CoxExpires 6 November 2023                [Page 8]