





Internet Engineering Task Force (IETF)                       W. Hargrave
Request for Comments: 8327                                         LONAP
BCP: 214                                                     M. Griswold
Category: Best Current Practice                                      20C
ISSN: 2070-1721                                              J. Snijders
                                                                     NTT
                                                             N. Hilliard
                                                                    INEX
                                                              March 2018


         Mitigating the Negative Impact of Maintenance through
                          BGP Session Culling

Abstract

   This document outlines an approach to mitigate the 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 that will be affected by
   maintenance are forcefully torn down before the actual maintenance
   activities commence.

Status of This Memo

   This memo documents an Internet Best Current Practice.

   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
   BCPs 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/rfc8327.















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Copyright Notice

   Copyright (c) 2018 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 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  BGP Session Culling . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Voluntary BGP Session Teardown Recommendations  . . . . .   4
       3.1.1.  Maintenance Considerations  . . . . . . . . . . . . .   4
     3.2.  Involuntary BGP Session Teardown Recommendations  . . . .   4
       3.2.1.  Packet-Filter Considerations  . . . . . . . . . . . .   5
       3.2.2.  Hardware Considerations . . . . . . . . . . . . . . .   5
     3.3.  Procedural Considerations . . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Example Packet Filters . . . . . . . . . . . . . . .   8
     A.1.  Example Configuration for Cisco IOS, IOS XR, and Arista
           EOS . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     A.2.  Example Configuration for Nokia SR OS . . . . . . . . . .   9
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10














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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 -- activities that otherwise would affect the flow
   of data between the BGP speakers.  BGP Session Culling is the
   practice of ensuring BGP sessions are forcefully torn down before
   commencing maintenance activities (that otherwise would affect the
   flow of data between the BGP speakers) on a lower-layer network.

   BGP Session Culling minimizes the amount of disruption that lower-
   layer network maintenance activities cause, by making BGP speakers
   preemptively converge onto alternative paths while the lower-layer
   network's forwarding plane remains fully operational.

   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 (see Section 6.5 of [RFC4271]), which is commonly between 90
   and 180 seconds.  The second value is implementation specific, but it
   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, and
   instead to monitor forwarding-plane activity while the culling is
   taking place and to 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",
   "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.  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 teardown
      of the potentially affected BGP session by issuing an
      Administrative Shutdown.



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   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 that 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 Prefix Independent Convergence (PIC) [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.

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

3.1.1.  Maintenance Considerations

   Initiators of the Administrative Shutdown MAY consider using Graceful
   Shutdown [RFC8326] 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 that 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
   performance.

   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.



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   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 subsection, through the application of a combined Layer 3
   and Layer 4 (Layer 3/4) packet filter deployed in the Caretaker's
   switched fabric.

3.2.1.  Packet-Filter Considerations

   The peering LAN prefixes used by the IXP form the control plane, and
   the 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., traffic forming part of the control plane of
      the system described, rather than multihop BGP traffic that merely
      transits.

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

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

   o  The packet filter MUST affect all Address Family Identifiers.

   Appendix A contains examples of correct packet filters for various
   platforms.

3.2.2.  Hardware Considerations

   Not all hardware is capable of deploying combined Layer 3/4 filters
   on Layer 2 ports; even on platforms that 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 that
      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 IEEE
      802.1AX Link Aggregate ports [IEEE802.1AX].





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   o  Failure of the Caretaker to apply filters to all IEEE 802.1AX Link
      Aggregate ports [IEEE802.1AX].

   o  Limitations in Access Control List (ACL) hardware mechanisms
      causing filters not to be applied.

   o  Fragmentation of ACL lookup memory causing transient ACL
      application problems that are resolved after ACL removal/
      reapplication.

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

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 be deployed for the
   duration of the maintenance only and be removed immediately after the
   maintenance is completed.  To prevent unnecessary 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.  Security Considerations

   There are no security considerations.

5.  IANA Considerations

   This document has no actions for IANA.











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6.  References

6.1.  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>.

   [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>.

6.2.  Informative References

   [BGP_PIC]  Bashandy, A., Ed., Filsfils, C., and P. Mohapatra, "BGP
              Prefix Independent Convergence", Work in Progress,
              draft-ietf-rtgwg-bgp-pic-06, November 2017.

   [IEEE802.1AX]
              IEEE, "IEEE Standard for Local and metropolitan area
              networks -- Link Aggregation", IEEE Std 802.1AX-2014,
              DOI 10.1109/IEEESTD.2014.7055197, December 2014,
              <http://ieeexplore.ieee.org/servlet/
              opac?punumber=6997981>.

   [RFC8203]  Snijders, J., Heitz, J., and J. Scudder, "BGP
              Administrative Shutdown Communication", RFC 8203,
              DOI 10.17487/RFC8203, July 2017,
              <https://www.rfc-editor.org/info/rfc8203>.

   [RFC8326]  Francois, P., Ed., Decraene, B., Ed., Pelsser, C., Patel,
              K., and C. Filsfils, "Graceful BGP Session Shutdown",
              RFC 8326, DOI 10.17487/8326, March 2018,
              <https://www.rfc-editor.org/info/rfc8326>.











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Appendix A.  Example Packet Filters

   This section includes examples of packet filters performing
   Involuntary BGP Session Teardown at an IXP using peering LAN prefixes
   192.0.2.0/24 and 2001:db8:2::/64 as its control plane.

   A repository of configuration examples for a number of assorted
   platforms can be found at
   <https://github.com/bgp/bgp-session-culling-config-examples>.

A.1.  Example Configuration for Cisco IOS, IOS XR, and Arista EOS

   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 192.0.2.0/24 eq bgp 192.0.2.0/24
      20 deny tcp 192.0.2.0/24 192.0.2.0/24 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.  Example Configuration for Nokia SR OS

   ip-filter 10 create
       filter-name "ACL IPv4 Permit All Except BGP"
       default-action forward
       entry 10 create
           match protocol tcp
               dst-ip 192.0.2.0/24
               src-ip 192.0.2.0/24
               port eq 179
           exit
           action
               drop
           exit
       exit
   exit

   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
           exit
           action
               drop
           exit
       exit
   exit

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












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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
   Carpenter.

Authors' Addresses

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

   Email: will@lonap.net


   Matt Griswold
   20C
   1658 Milwaukee Ave # 100-4506
   Chicago, IL  60647
   United States of America

   Email: grizz@20c.com


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

   Email: job@ntt.net


   Nick Hilliard
   INEX
   4027 Kingswood Road
   Dublin  24
   Ireland

   Email: nick@inex.ie







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