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Global Routing Operations                                    W. Hargrave
Internet-Draft                                                     LONAP
Intended status: Best Current Practice                       M. Griswold
Expires: September 13, 2017                                          20C
                                                             J. Snijders
                                                                     NTT
                                                             N. Hilliard
                                                                    INEX
                                                          March 12, 2017


 Mitigating Negative Impact of Maintenance through BGP Session Culling
                 draft-iops-grow-bgp-session-culling-00

Abstract

   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
   commence.

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 http://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 September 13, 2017.

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
   (http://trustee.ietf.org/license-info) 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.  BGP Session Culling . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Voluntary BGP Session Teardown Recommendations  . . . . .   3
       2.1.1.  Maintenance Communication Considerations  . . . . . .   3
     2.2.  Involuntary BGP Session Teardown Recommendations  . . . .   3
       2.2.1.  Packet Filter Considerations  . . . . . . . . . . . .   4
       2.2.2.  Hardware Considerations . . . . . . . . . . . . . . .   4
     2.3.  Monitoring Considerations . . . . . . . . . . . . . . . .   5
   3.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Example packet filters . . . . . . . . . . . . . . .   6
     A.1.  Juniper Junos Layer 2 Firewall Example Configuration  . .   6
     A.2.  Arista EOS Firewall Example Configuration . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   In network topologies where BGP speaking routers are directly
   attached to each other, or use fault detection mechanisms such as BFD
   [RFC5880], detecting and acting upon a link down event (for example
   when someone yanks the physical connector) in a timely fashion is
   straightforward.

   However, in topologies where upper layer fast fault detection
   mechanisms are unavailable and the lower layer topology is hidden
   from the BGP speakers, operators rely on BGP Hold Timer Expiration
   (section 6.5 of [RFC4271]) to initiate traffic rerouting.  Common BGP
   Hold Timer values are anywhere between 90 and 180 seconds, which
   implies a window of 90 to 180 seconds during which traffic
   blackholing will occur if the lower layer network is not able to
   forward traffic.

   BGP Session Culling is the practice of ensuring BGP sessions are
   forcefully torn down before maintenance activities on a lower layer




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   network commence, which otherwise would affect the flow of data
   between the BGP speakers.

2.  BGP Session Culling

   From the viewpoint of the IP network 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 BGP control-plane traffic in the upper layer,
      causing the BGP Hold Timers of the affected BGP session to expire,
      subsequently triggering rerouting of end user traffic.

2.1.  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 would
   do well to Administratively Shutdown the 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.

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

2.1.1.  Maintenance Communication Considerations

   Initiators of the Administrative Shutdown are encouraged to use
   Shutdown Communication [I-D.ietf-idr-shutdown] to inform the remote
   side on the nature and duration of the maintenance activities.

2.2.  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.




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   Operational experience shows many network operators are unable to
   carry out the Voluntary BGP Session Teardown recommendations, because
   of the operational cost and risk of co-ordinating 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
   densely meshed multi-node layer-2 fabric, the caretaker of the fabric
   could opt to cull BGP sessions on behalf of the stakeholders
   connected to the fabric.

   Such culling of control-plane traffic will pre-empt 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 through the
   application of a combined layer-3 and layer-4 packet filter deployed
   in the switched fabric itself.

2.2.1.  Packet Filter Considerations

   The packet filter should be designed and specified in a way that:

   o  only affect link-local BGP traffic i.e. forming part of the
      control plane of the system described, rather than multihop BGP
      which merely transits

   o  only affect BGP, i.e. TCP/179

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

   o  affect all relevant AFIs

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

2.2.2.  Hardware Considerations

   Not all hardware is capable of deploying layer 3 / layer 4 filters on
   layer 2 ports, and even on platforms which support the feature,
   documented limitations may exist or hardware resource allocation
   failures may occur during filter deployment which may cause
   unexpected result.  These problems may include:





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   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 operator to apply filters to all 802.3ad Link
      Aggregate ports

   o  Limitations in ACL hardware mechanisms causing filters not to be
      applied.

   o  Fragmentation of ACL lookup memory causing transient ACL
      application problems which 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 operator 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.

2.3.  Monitoring Considerations

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

3.  Acknowledgments

   The authors would like to thank the following people for their
   contributions to this document: Saku Ytti.

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

   [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,
              <http://www.rfc-editor.org/info/rfc4271>.

6.2.  Informative References

   [I-D.ietf-idr-shutdown]
              Snijders, J., Heitz, J., and J. Scudder, "BGP
              Administrative Shutdown Communication", draft-ietf-idr-
              shutdown-07 (work in progress), March 2017.

   [I-D.ietf-rtgwg-bgp-pic]
              Bashandy, A., Filsfils, C., and P. Mohapatra, "BGP Prefix
              Independent Convergence", draft-ietf-rtgwg-bgp-pic-01
              (work in progress), June 2016.

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

Appendix A.  Example packet filters

   Example packet filters for "Involuntary BGP Session Teardown" at an
   IXP with LAN prefixes 192.0.2.0/24 and 2001:db8:2::/64.

A.1.  Juniper Junos Layer 2 Firewall Example Configuration

   > show configuration firewall family ethernet-switching filter cull
   term towards_peeringlan-v4 {
       from {
           ip-version {
               ipv4 {
                   destination-port bgp;
                   ip-source-address {
                       192.0.2.0/24;
                   }
                   ip-destination-address {
                       192.0.2.0/24;
                   }
                   ip-protocol tcp;
               }
           }
       }



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       then discard;
   }
   term from_peeringlan-v4 {
       from {
           ip-version {
               ipv4 {
                   source-port bgp;
                   ip-source-address {
                       192.0.2.0/24;
                   }
                   ip-destination-address {
                       192.0.2.0/24;
                   }
                   ip-protocol tcp;
               }
           }
       }
       then discard;
   }
   term towards_peeringlan-v6 {
       from {
           ip-version {
               ipv6 {
                   next-header tcp;
                   destination-port bgp;
                   ip6-source-address {
                       2001:db8:2::/64;
                   }
                   ip6-destination-address {
                       2001:db8:2::/64;
                   }
               }
           }
       }
       then discard;
   }
   term from_peeringlan-v6 {
       from {
           ip-version {
               ipv6 {
                   next-header tcp;
                   source-port bgp;
                   ip6-source-address {
                       2001:db8:2::/64;
                   }
                   ip6-destination-address {
                       2001:db8:2::/64;
                   }



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               }
           }
       }
       then discard;
   }
   term rest {
       then accept;
   }

   > show configuration interfaces xe-0/0/46
   description "IXP participant affected by maintenance"
   unit 0 {
       family ethernet-switching {
           filter {
               input cull;
           }
       }
   }

A.2.  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 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
   !

Authors' Addresses

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

   Email: will@lonap.net





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   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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