Internet DRAFT - draft-iops-grow-bgp-session-culling
draft-iops-grow-bgp-session-culling
Global Routing Operations W. Hargrave
Internet-Draft LONAP
Intended status: Best Current Practice M. Griswold
Expires: September 28, 2017 20C
J. Snijders
NTT
N. Hilliard
INEX
March 27, 2017
Mitigating Negative Impact of Maintenance through BGP Session Culling
draft-iops-grow-bgp-session-culling-01
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
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 28, 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
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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 . . . . . . . . . . . . . . . . . 6
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 . . . . . . . . 7
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 gracefully 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 governed by the BGP Hold Timer
(section 6.5 of [RFC4271]), commonly between 90 and 180 seconds, The
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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 the
operator 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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. 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.
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 Administratively 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
state.
3.1.1. Maintenance Considerations
Initiators of the Administrative Shutdown could consider to use
[Graceful Shutdown] to facilitate smooth drainage of traffic prior to
session tear down, and the Shutdown Communication
[I-D.ietf-idr-shutdown] 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 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.
3.2.1. Packet Filter Considerations
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. forming part of the control plane of the
system described, rather than multihop BGP traffic which merely
transits
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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
direction
o The packet filter MUST affect all relevant AFIs
Appendix A contains examples of correct packet filters for various
platforms.
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 support the feature,
documented 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 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.
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3.3. Procedural 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.
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, and Tore
Anderson.
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,
<http://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,
<http://www.rfc-editor.org/info/rfc4271>.
7.2. 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.
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[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.
7.3. URIs
[1] https://github.com/bgp/bgp-session-culling-config-examples
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 repository of configuration examples for a number of assorted
platforms can be found at github.com/bgp/bgp-session-culling-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 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
!
A.2. Nokia SR OS Filter Example Configuration
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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
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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