draft-ietf-grow-bgp-session-culling-02.txt   draft-ietf-grow-bgp-session-culling-03.txt 
Global Routing Operations W. Hargrave Global Routing Operations W. Hargrave
Internet-Draft LONAP Internet-Draft LONAP
Intended status: Best Current Practice M. Griswold Intended status: Best Current Practice M. Griswold
Expires: January 4, 2018 20C Expires: February 19, 2018 20C
J. Snijders J. Snijders
NTT NTT
N. Hilliard N. Hilliard
INEX INEX
July 3, 2017 August 18, 2017
Mitigating Negative Impact of Maintenance through BGP Session Culling Mitigating Negative Impact of Maintenance through BGP Session Culling
draft-ietf-grow-bgp-session-culling-02 draft-ietf-grow-bgp-session-culling-03
Abstract Abstract
This document outlines an approach to mitigate negative impact on This document outlines an approach to mitigate negative impact on
networks resulting from maintenance activities. It includes guidance networks resulting from maintenance activities. It includes guidance
for both IP networks and Internet Exchange Points (IXPs). The for both IP networks and Internet Exchange Points (IXPs). The
approach is to ensure BGP-4 sessions affected by the maintenance are approach is to ensure BGP-4 sessions affected by the maintenance are
forcefully torn down before the actual maintenance activities forcefully torn down before the actual maintenance activities
commence. commence.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 4, 2018. This Internet-Draft will expire on February 19, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 43 skipping to change at page 2, line 43
1. Introduction 1. Introduction
BGP Session Culling is the practice of ensuring BGP sessions are BGP Session Culling is the practice of ensuring BGP sessions are
forcefully torn down before maintenance activities on a lower layer forcefully torn down before maintenance activities on a lower layer
network commence, which otherwise would affect the flow of data network commence, which otherwise would affect the flow of data
between the BGP speakers. between the BGP speakers.
BGP Session Culling ensures that lower layer network maintenance BGP Session Culling ensures that lower layer network maintenance
activities cause the minimum possible amount of disruption, by activities cause the minimum possible amount of disruption, by
causing BGP speakers to preemptively gracefully converge onto causing BGP speakers to preemptively converge onto alternative paths
alternative paths while the lower layer network's forwarding plane while the lower layer network's forwarding plane remains fully
remains fully operational. operational.
The grace period required for a successful application of BGP Session 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 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 session, plus the time required for the BGP speaker to converge onto
alternative paths. The first value is governed by the BGP Hold Timer alternative paths. The first value is often governed by the BGP Hold
(section 6.5 of [RFC4271]), commonly between 90 and 180 seconds, The Timer (section 6.5 of [RFC4271]), commonly between 90 and 180
second value is implementation specific, but could be as much as 15 seconds. The second value is implementation specific, but could be
minutes when a router with a slow control-plane is receiving a full as much as 15 minutes when a router with a slow control-plane is
set of Internet routes. receiving a full set of Internet routes.
Throughout this document the "Caretaker" is defined to be the Throughout this document the "Caretaker" is defined to be the
operator of the lower layer network, while "Operators" directly operator of the lower layer network, while "Operators" directly
administrate the BGP speakers. Operators and Caretakers implementing administrate the BGP speakers. Operators and Caretakers implementing
BGP Session Culling are encouraged to avoid using a fixed grace BGP Session Culling are encouraged to avoid using a fixed grace
period, but instead monitor forwarding plane activity while the period, but instead monitor forwarding plane activity while the
culling is taking place and consider it complete once traffic levels culling is taking place and consider it complete once traffic levels
have dropped to a minimum (Section 3.3). have dropped to a minimum (Section 3.3).
2. Requirements Language 2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
3. BGP Session Culling 3. BGP Session Culling
From the viewpoint of the IP network operator, there are two types of From the viewpoint of the IP network operator, there are two types of
BGP Session Culling: BGP Session Culling:
Voluntary BGP Session Teardown: The operator initiates the tear down Voluntary BGP Session Teardown: The Operator initiates the tear down
of the potentially affected BGP session by issuing an of the potentially affected BGP session by issuing an
Administrative Shutdown. Administrative Shutdown.
Involuntary BGP Session Teardown: The caretaker of the lower layer Involuntary BGP Session Teardown: The Caretaker of the lower layer
network disrupts BGP control-plane traffic in the upper layer, network disrupts BGP control-plane traffic in the upper layer,
causing the BGP Hold Timers of the affected BGP session to expire, causing the BGP Hold Timers of the affected BGP session to expire,
subsequently triggering rerouting of end user traffic. subsequently triggering rerouting of end user traffic.
3.1. Voluntary BGP Session Teardown Recommendations 3.1. Voluntary BGP Session Teardown Recommendations
Before an operator commences activities which can cause disruption to Before an Operator commences activities which can cause disruption to
the flow of data through the lower layer network, an operator can the flow of data through the lower layer network, an operator can
reduce loss of traffic by issuing an Administratively Shutdown to all reduce loss of traffic by issuing an administrative shutdown to all
BGP sessions running across the lower layer network and wait a few BGP sessions running across the lower layer network and wait a few
minutes for data-plane traffic to subside. minutes for data-plane traffic to subside.
While architectures exist to facilitate quick network reconvergence While architectures exist to facilitate quick network reconvergence
(such as BGP PIC [I-D.ietf-rtgwg-bgp-pic]), an operator cannot assume (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 the remote side has such capabilities. As such, a grace period
between the Administrative Shutdown and the impacting maintenance between the Administrative Shutdown and the impacting maintenance
activities is warranted. activities is warranted.
After the maintenance activities have concluded, the operator is After the maintenance activities have concluded, the operator is
expected to restore the BGP sessions to their original Administrative expected to restore the BGP sessions to their original Administrative
state. state.
3.1.1. Maintenance Considerations 3.1.1. Maintenance Considerations
Initiators of the Administrative Shutdown could consider to use Initiators of the administrative shutdown could consider using
Graceful Shutdown [I-D.ietf-grow-bgp-gshut] to facilitate smooth Graceful Shutdown [I-D.ietf-grow-bgp-gshut] to facilitate smooth
drainage of traffic prior to session tear down, and the Shutdown drainage of traffic prior to session tear down, and the Shutdown
Communication [I-D.ietf-idr-shutdown] to inform the remote side on Communication [I-D.ietf-idr-shutdown] to inform the remote side on
the nature and duration of the maintenance activities. the nature and duration of the maintenance activities.
3.2. Involuntary BGP Session Teardown Recommendations 3.2. Involuntary BGP Session Teardown Recommendations
In the case where multilateral interconnection between BGP speakers In the case where multilateral interconnection between BGP speakers
is facilitated through a switched layer-2 fabric, such as commonly is facilitated through a switched layer-2 fabric, such as commonly
seen at Internet Exchange Points (IXPs), different operational seen at Internet Exchange Points (IXPs), different operational
considerations can apply. considerations can apply.
Operational experience shows many network operators are unable to Operational experience shows many network operators are unable to
carry out the Voluntary BGP Session Teardown recommendations, because carry out the Voluntary BGP Session Teardown recommendations, because
of the operational cost and risk of co-ordinating the two of the operational cost and risk of co-ordinating the two
configuration changes required. This has an adverse affect on configuration changes required. This has an adverse affect on
Internet performance. Internet performance.
In the absence of notifications from the lower layer (e.g. ethernet In the absence notifications from the lower layer (e.g. ethernet link
link down) consistent with the planned maintenance activities in a down) consistent with the planned maintenance activities in a
densely meshed multi-node layer-2 fabric, the caretaker of the fabric switched layer-2 fabric, the Caretaker of the fabric could choose to
could opt to cull BGP sessions on behalf of the stakeholders cull BGP sessions on behalf of the Operators connected to the fabric.
connected to the fabric.
Such culling of control-plane traffic will pre-empt the loss of end- 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 user traffic, by causing the expiration of BGP Hold Timers ahead of
the moment where the expiration would occur without intervention from the moment where the expiration would occur without intervention from
the fabric's caretaker. the fabric's Caretaker.
In this scenario, BGP Session Culling is accomplished through the In this scenario, BGP Session Culling is accomplished through the
application of a combined layer-3 and layer-4 packet filter deployed application of a combined layer-3 and layer-4 packet filter deployed
in the switched fabric itself. in the switched fabric itself.
3.2.1. Packet Filter Considerations 3.2.1. Packet Filter Considerations
The following considerations apply to the packet filter design: The following considerations apply to the packet filter design:
o The packet filter MUST only affect BGP traffic specific to the 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 layer-2 fabric, i.e. forming part of the control plane of the
system described, rather than multihop BGP traffic which merely system described, rather than multihop BGP traffic which merely
transits transits
o The packet filter MUST only affect BGP, i.e. TCP/179 o The packet filter MUST only affect BGP, i.e. TCP/179
o The packet filter SHOULD make provision for the bidirectional o The packet filter SHOULD make provision for the bidirectional
nature of BGP, i.e. that sessions may be established in either nature of BGP, i.e. that sessions may be established in either
direction direction
o The packet filter MUST affect all relevant AFIs o The packet filter MUST affect all relevant Address Family
Identifiers.
Appendix A contains examples of correct packet filters for various Appendix A contains examples of correct packet filters for various
platforms. platforms.
3.2.2. Hardware Considerations 3.2.2. Hardware Considerations
Not all hardware is capable of deploying layer 3 / layer 4 filters on Not all hardware is capable of deploying Layer 3 / Layer 4 filters on
layer 2 ports, and even on platforms which support the feature, Layer 2 ports, and even on platforms which claim support for such a
documented limitations may exist or hardware resource allocation feature, limitations may exist or hardware resource allocation
failures may occur during filter deployment which may cause failures may occur during filter deployment which may cause
unexpected results. These problems may include: unexpected results. These problems may include:
o Platform inability to apply layer 3/4 filters on ports which o Platform inability to apply layer 3/4 filters on ports which
already have layer 2 filters applied already have layer 2 filters applied
o Layer 3/4 filters supported for IPv4 but not for IPv6 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 o Layer 3/4 filters supported on physical ports, but not on 802.3ad
Link Aggregate ports Link Aggregate ports
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o Reduction in hardware ACL capacity if the platform enables o Reduction in hardware ACL capacity if the platform enables
lossless ACL application lossless ACL application
It is advisable for the operator to be aware of the limitations of It is advisable for the operator to be aware of the limitations of
their hardware, and to thoroughly test all complicated configurations their hardware, and to thoroughly test all complicated configurations
in advance to ensure that problems don't occur during production in advance to ensure that problems don't occur during production
deployments. deployments.
3.3. Procedural Considerations 3.3. Procedural Considerations
The caretaker of the lower layer can monitor data-plane traffic (e.g. The Caretaker of the lower layer network can monitor data-plane
interface counters) and carry out the maintenance without impact to traffic (e.g. interface counters) and carry out the maintenance
traffic once session culling is complete. without impact to traffic once session culling is complete.
It is recommended that the packet filters are only deployed for the It is recommended that the packet filters are only deployed for the
duration of the maintenance and immediately removed after the duration of the maintenance and immediately removed after the
maintenance. To prevent unnecessarily troubleshooting, it is maintenance. To prevent unnecessarily troubleshooting, it is
RECOMMENDED that caretakers notify the affected operators before the RECOMMENDED that Caretakers notify the affected operators before the
maintenance takes place, and make it explicit that the Involuntary maintenance takes place, and make it explicit that the Involuntary
BGP Session Culling methodology will be applied. BGP Session Culling methodology will be applied.
4. Acknowledgments 4. Acknowledgments
The authors would like to thank the following people for their The authors would like to thank the following people for their
contributions to this document: Saku Ytti, Greg Hankins, James contributions to this document: Saku Ytti, Greg Hankins, James
Bensley, Wolfgang Tremmel, Daniel Roesen, Bruno Decraene, and Tore Bensley, Wolfgang Tremmel, Daniel Roesen, Bruno Decraene, Tore
Anderson. Anderson and John Heasley.
5. Security Considerations 5. Security Considerations
There are no security considerations. There are no security considerations.
6. IANA Considerations 6. IANA Considerations
This document has no actions for IANA. This document has no actions for IANA.
7. References 7. References
7.1. Normative References 7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271, Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006, DOI 10.17487/RFC4271, January 2006, <https://www.rfc-
<http://www.rfc-editor.org/info/rfc4271>. editor.org/info/rfc4271>.
7.2. Informative References 7.2. Informative References
[I-D.ietf-grow-bgp-gshut] [I-D.ietf-grow-bgp-gshut]
Francois, P., Decraene, B., Pelsser, C., Patel, K., and C. Francois, P., Decraene, B., Pelsser, C., Patel, K., and C.
Filsfils, "Graceful BGP session shutdown", draft-ietf- Filsfils, "Graceful BGP session shutdown", draft-ietf-
grow-bgp-gshut-09 (work in progress), June 2017. grow-bgp-gshut-09 (work in progress), July 2017.
[I-D.ietf-idr-shutdown] [I-D.ietf-idr-shutdown]
Snijders, J., Heitz, J., and J. Scudder, "BGP Snijders, J., Heitz, J., and J. Scudder, "BGP
Administrative Shutdown Communication", draft-ietf-idr- Administrative Shutdown Communication", draft-ietf-idr-
shutdown-10 (work in progress), June 2017. shutdown-10 (work in progress), June 2017.
[I-D.ietf-rtgwg-bgp-pic] [I-D.ietf-rtgwg-bgp-pic]
Bashandy, A., Filsfils, C., and P. Mohapatra, "BGP Prefix Bashandy, A., Filsfils, C., and P. Mohapatra, "BGP Prefix
Independent Convergence", draft-ietf-rtgwg-bgp-pic-05 Independent Convergence", draft-ietf-rtgwg-bgp-pic-05
(work in progress), May 2017. (work in progress), May 2017.
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