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Mitigating the Negative Impact of Maintenance through BGP Session Culling

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8327.
Authors Will Hargrave , Matt Griswold , Job Snijders , Nick Hilliard
Last updated 2020-01-21 (Latest revision 2017-09-28)
Replaces draft-iops-grow-bgp-session-culling
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Best Current Practice
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Chris Morrow
Shepherd write-up Show Last changed 2017-09-06
IESG IESG state Became RFC 8327 (Best Current Practice)
Action Holders
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Warren "Ace" Kumari
Send notices to Christopher Morrow <>
IANA IANA review state IANA OK - No Actions Needed
IANA action state No IANA Actions
Global Routing Operations                                    W. Hargrave
Internet-Draft                                                     LONAP
Intended status: Best Current Practice                       M. Griswold
Expires: April 1, 2018                                               20C
                                                             J. Snijders
                                                             N. Hilliard
                                                      September 28, 2017

 Mitigating Negative Impact of Maintenance through BGP Session Culling


   This document outlines an approach to mitigate negative impact on
   networks resulting from maintenance activities.  It includes guidance
   for both IP networks and Internet Exchange Points (IXPs).  The
   approach is to ensure BGP-4 sessions affected by the maintenance are
   forcefully torn down before the actual maintenance activities

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

   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 April 1, 2018.

Copyright Notice

   Copyright (c) 2017 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
   ( in effect on the date of

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   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.  BGP Session Culling . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Voluntary BGP Session Teardown Recommendations  . . . . .   3
       3.1.1.  Maintenance Considerations  . . . . . . . . . . . . .   4
     3.2.  Involuntary BGP Session Teardown Recommendations  . . . .   4
       3.2.1.  Packet Filter Considerations  . . . . . . . . . . . .   4
       3.2.2.  Hardware Considerations . . . . . . . . . . . . . . .   5
     3.3.  Procedural Considerations . . . . . . . . . . . . . . . .   6
   4.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Example packet filters . . . . . . . . . . . . . . .   7
     A.1.  Cisco IOS, IOS XR & Arista EOS Firewall Example
           Configuration . . . . . . . . . . . . . . . . . . . . . .   7
     A.2.  Nokia SR OS Filter Example Configuration  . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   BGP Session Culling is the practice of ensuring BGP sessions are
   forcefully torn down before maintenance activities on a lower layer
   network commence, which otherwise would affect the flow of data
   between the BGP speakers.

   BGP Session Culling ensures that lower layer network maintenance
   activities cause the minimum possible amount of disruption, by
   causing BGP speakers to preemptively converge onto alternative paths
   while the lower layer network's forwarding plane remains fully

   The grace period required for a successful application of BGP Session
   Culling is the sum of the time needed to detect the loss of the BGP
   session, plus the time required for the BGP speaker to converge onto
   alternative paths.  The first value is often governed by the BGP Hold
   Timer (section 6.5 of [RFC4271]), commonly between 90 and 180

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   seconds.  The second value is implementation specific, but could be
   as much as 15 minutes when a router with a slow control-plane is
   receiving a full set of Internet routes.

   Throughout this document the "Caretaker" is defined to be in control
   of the lower layer network, while "Operators" directly administrate
   the BGP speakers.  Operators and Caretakers implementing BGP Session
   Culling are encouraged to avoid using a fixed grace period, but
   instead monitor forwarding plane activity while the culling is taking
   place and consider it complete once traffic levels have dropped to a
   minimum (Section 3.3).

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  BGP Session Culling

   From the viewpoint of the Operator, there are two types of BGP
   Session Culling:

   Voluntary BGP Session Teardown:  The Operator initiates the tear down
      of the potentially affected BGP session by issuing an
      Administrative Shutdown.

   Involuntary BGP Session Teardown:  The Caretaker of the lower layer
      network disrupts (higher layer) BGP control-plane traffic, causing
      the BGP Hold Timers of the affected BGP session to expire,
      subsequently triggering rerouting of end user traffic.

3.1.  Voluntary BGP Session Teardown Recommendations

   Before an Operator commences activities which can cause disruption to
   the flow of data through the lower layer network, an Operator can
   reduce loss of traffic by issuing an administrative shutdown to all
   BGP sessions running across the lower layer network and wait a few
   minutes for data-plane traffic to subside.

   While architectures exist to facilitate quick network reconvergence
   (such as BGP PIC [I-D.ietf-rtgwg-bgp-pic]), an Operator cannot assume
   the remote side has such capabilities.  As such, a grace period
   between the Administrative Shutdown and the impacting maintenance
   activities is warranted.

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   After the maintenance activities have concluded, the Operator is
   expected to restore the BGP sessions to their original Administrative

3.1.1.  Maintenance Considerations

   Initiators of the administrative shutdown MAY consider using Graceful
   Shutdown [I-D.ietf-grow-bgp-gshut] to facilitate smooth drainage of
   traffic prior to session tear down, and the Shutdown Communication
   [RFC8203] to inform the remote side on the nature and duration of the
   maintenance activities.

3.2.  Involuntary BGP Session Teardown Recommendations

   In the case where multilateral interconnection between BGP speakers
   is facilitated through a switched layer-2 fabric, such as commonly
   seen at Internet Exchange Points (IXPs), different operational
   considerations can apply.

   Operational experience shows many Operators are unable to carry out
   the Voluntary BGP Session Teardown recommendations, because of the
   operational cost and risk of coordinating the two configuration
   changes required.  This has an adverse affect on Internet

   In the absence of notifications from the lower layer (e.g.  Ethernet
   link down) consistent with the planned maintenance activities in a
   switched layer-2 fabric, the Caretaker of the fabric could choose to
   cull BGP sessions on behalf of the Operators connected to the fabric.

   Such culling of control-plane traffic will preempt the loss of end-
   user traffic, by causing the expiration of BGP Hold Timers ahead of
   the moment where the expiration would occur without intervention from
   the fabric's Caretaker.

   In this scenario, BGP Session Culling is accomplished as described in
   the next sub-section, through the application of a combined layer-3
   and layer-4 packet filter deployed in the Caretaker's switched

3.2.1.  Packet Filter Considerations

   The peering LAN prefixes used by the IXP form the control plane, and
   following considerations apply to the packet filter design:

   o  The packet filter MUST only affect BGP traffic specific to the
      layer-2 fabric, i.e. forming part of the control plane of the

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      system described, rather than multihop BGP traffic which merely

   o  The packet filter MUST only affect BGP, i.e. TCP/179.

   o  The packet filter SHOULD make provision for the bidirectional
      nature of BGP, i.e. that sessions may be established in either

   o  The packet filter MUST affect all Address Family Identifiers.

   Appendix A contains examples of correct packet filters for various

3.2.2.  Hardware Considerations

   Not all hardware is capable of deploying Layer 3 / Layer 4 filters on
   Layer 2 ports, and even on platforms which claim support for such a
   feature, limitations may exist or hardware resource allocation
   failures may occur during filter deployment which may cause
   unexpected results.  These problems may include:

   o  Platform inability to apply layer 3/4 filters on ports which
      already have layer 2 filters applied.

   o  Layer 3/4 filters supported for IPv4 but not for IPv6.

   o  Layer 3/4 filters supported on physical ports, but not on 802.3ad
      Link Aggregate ports.

   o  Failure of the Caretaker to apply filters to all 802.3ad Link
      Aggregate ports.

   o  Limitations in ACL hardware mechanisms causing filters not to be

   o  Fragmentation of ACL lookup memory causing transient ACL
      application problems which are resolved after ACL removal /

   o  Temporary service loss during hardware programming

   o  Reduction in hardware ACL capacity if the platform enables
      lossless ACL application.

   It is advisable for the Caretaker to be aware of the limitations of
   their hardware, and to thoroughly test all complicated configurations

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   in advance to ensure that problems don't occur during production

3.3.  Procedural Considerations

   The Caretaker of the lower layer network can monitor data-plane
   traffic (e.g. interface counters) and carry out the maintenance
   without impact to traffic once session culling is complete.

   It is recommended that the packet filters are only deployed for the
   duration of the maintenance and immediately removed after the
   maintenance.  To prevent unnecessarily troubleshooting, it is
   RECOMMENDED that Caretakers notify the affected Operators before the
   maintenance takes place, and make it explicit that the Involuntary
   BGP Session Culling methodology will be applied.

4.  Acknowledgments

   The authors would like to thank the following people for their
   contributions to this document: Saku Ytti, Greg Hankins, James
   Bensley, Wolfgang Tremmel, Daniel Roesen, Bruno Decraene, Tore
   Anderson, John Heasley, Warren Kumari, Stig Venaas, and Brian

5.  Security Considerations

   There are no security considerations.

6.  IANA Considerations

   This document has no actions for IANA.

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,

   [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,

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7.2.  Informative References

              Francois, P., Decraene, B., Pelsser, C., Patel, K., and C.
              Filsfils, "Graceful BGP session shutdown", draft-ietf-
              grow-bgp-gshut-11 (work in progress), September 2017.

              Bashandy, A., Filsfils, C., and P. Mohapatra, "BGP Prefix
              Independent Convergence", draft-ietf-rtgwg-bgp-pic-05
              (work in progress), May 2017.

   [RFC8203]  Snijders, J., Heitz, J., and J. Scudder, "BGP
              Administrative Shutdown Communication", RFC 8203,
              DOI 10.17487/RFC8203, July 2017,

7.3.  URIs


Appendix A.  Example packet filters

   Example packet filters for "Involuntary BGP Session Teardown" at an
   IXP using peering LAN prefixes and 2001:db8:2::/64 as
   its control plane.

   A repository of configuration examples for a number of assorted
   platforms can be found at
   config-examples [1].

A.1.  Cisco IOS, IOS XR & Arista EOS Firewall Example Configuration

   ipv6 access-list acl-ipv6-permit-all-except-bgp
      10 deny tcp 2001:db8:2::/64 eq bgp 2001:db8:2::/64
      20 deny tcp 2001:db8:2::/64 2001:db8:2::/64 eq bgp
      30 permit ipv6 any any
   ip access-list acl-ipv4-permit-all-except-bgp
      10 deny tcp eq bgp
      20 deny tcp eq bgp
      30 permit ip any any
   interface Ethernet33
      description IXP Participant Affected by Maintenance
      ip access-group acl-ipv4-permit-all-except-bgp in
      ipv6 access-group acl-ipv6-permit-all-except-bgp in

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A.2.  Nokia SR OS Filter Example Configuration

   ip-filter 10 create
       filter-name "ACL IPv4 Permit All Except BGP"
       default-action forward
       entry 10 create
           match protocol tcp
               port eq 179

   ipv6-filter 10 create
       filter-name "ACL IPv6 Permit All Except BGP"
       default-action forward
       entry 10 create
           match next-header tcp
               dst-ip 2001:db8:2::/64
               src-ip 2001:db8:2::/64
               port eq 179

   interface "port-1/1/1"
       description "IXP Participant Affected by Maintenance"
           filter ip 10
           filter ipv6 10

Authors' Addresses

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   Will Hargrave
   LONAP Ltd
   5 Fleet Place
   London  EC4M 7RD
   United Kingdom


   Matt Griswold
   1658 Milwaukee Ave # 100-4506
   Chicago, IL  60647
   United States of America


   Job Snijders
   NTT Communications
   Theodorus Majofskistraat 100
   Amsterdam  1065 SZ
   The Netherlands


   Nick Hilliard
   4027 Kingswood Road
   Dublin  24


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