draft-ietf-grow-bgp-gshut-11.txt   draft-ietf-grow-bgp-gshut-12.txt 
Network Working Group P. Francois, Ed. Network Working Group P. Francois, Ed.
Internet-Draft Individual Contributor Internet-Draft Individual Contributor
Intended status: Informational B. Decraene, Ed. Intended status: Informational B. Decraene, Ed.
Expires: March 24, 2018 Orange Expires: April 14, 2018 Orange
C. Pelsser C. Pelsser
Strasbourg University Strasbourg University
K. Patel K. Patel
Arrcus, Inc. Arrcus, Inc.
C. Filsfils C. Filsfils
Cisco Systems Cisco Systems
September 20, 2017 October 11, 2017
Graceful BGP session shutdown Graceful BGP session shutdown
draft-ietf-grow-bgp-gshut-11 draft-ietf-grow-bgp-gshut-12
Abstract Abstract
This draft standardizes a new well-known BGP community This draft standardizes a new well-known BGP community
GRACEFUL_SHUTDOWN to signal the graceful shutdown of paths. This GRACEFUL_SHUTDOWN to signal the graceful shutdown of paths. This
draft also describes operational procedures which use this community draft also describes operational procedures which use this community
to reduce the amount of traffic lost when BGP peering sessions are to reduce the amount of traffic lost when BGP peering sessions are
about to be shut down deliberately, e.g. for planned maintenance. about to be shut down deliberately, e.g. for planned maintenance.
Status of This Memo Status of This Memo
skipping to change at page 1, line 41 skipping to change at page 1, line 41
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 https://datatracker.ietf.org/drafts/current/. Drafts is at https://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 March 24, 2018. This Internet-Draft will expire on April 14, 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
(https://trustee.ietf.org/license-info) in effect on the date of (https://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 50 skipping to change at page 2, line 50
Routing changes in BGP can be caused by planned maintenance Routing changes in BGP can be caused by planned maintenance
operations. This document defines a well-known community [RFC1997], operations. This document defines a well-known community [RFC1997],
called GRACEFUL_SHUTDOWN, for the purpose of reducing the management called GRACEFUL_SHUTDOWN, for the purpose of reducing the management
overhead of gracefully shutting down BGP sessions. The well-known overhead of gracefully shutting down BGP sessions. The well-known
community allows implementers to provide an automated graceful community allows implementers to provide an automated graceful
shutdown mechanism that does not require any router reconfiguration shutdown mechanism that does not require any router reconfiguration
at maintenance time. at maintenance time.
This document discusses operational procedures to be applied in order This document discusses operational procedures to be applied in order
to reduce or eliminate loss of packets during a maintenance. Loss to reduce or eliminate loss of packets during a maintenance
comes from transient lack of reachability during BGP convergence operation. Loss comes from transient lack of reachability during BGP
which follows the shutdown of an EBGP peering session between two convergence which follows the shutdown of an EBGP peering session
Autonomous System Border Routers (ASBR). between two Autonomous System Border Routers (ASBR).
This document presents procedures for the cases where the forwarding This document presents procedures for the cases where the forwarding
plane is impacted by the maintenance, hence when the use of Graceful plane is impacted by the maintenance, hence when the use of Graceful
Restart does not apply. Restart does not apply.
The procedures described in this document can be applied to reduce or The procedures described in this document can be applied to reduce or
avoid packet loss for outbound and inbound traffic flows initially avoid packet loss for outbound and inbound traffic flows initially
forwarded along the peering link to be shut down. These procedures forwarded along the peering link to be shut down. These procedures
trigger, in both ASes, rerouting to alternate paths if they exist trigger, in both Autonomous Sytems (AS), rerouting to alternate paths
within the AS, while allowing the use of the old path until alternate if they exist within the AS, while allowing the use of the old path
ones are learned. This ensures that routers always have a valid until alternate ones are learned. This ensures that routers always
route available during the convergence process. have a valid route available during the convergence process.
The goal of the document is to meet the requirements described in The goal of the document is to meet the requirements described in
[RFC6198] at best, without changing the BGP protocol. [RFC6198] at best, without changing the BGP protocol.
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 8174 [RFC8174].
2. Terminology 2. Terminology
graceful shutdown initiator: a router on which the session shutdown graceful shutdown initiator: a router on which the session shutdown
is performed for the maintenance. is performed for the maintenance.
graceful shutdown receiver: a router that has a BGP session, to be graceful shutdown receiver: a router that has a BGP session, to be
shutdown, with the graceful shutdown initiator. shutdown, with the graceful shutdown initiator.
3. Packet loss upon manual EBGP session shutdown 3. Packet loss upon manual EBGP session shutdown
skipping to change at page 4, line 14 skipping to change at page 4, line 14
4. EBGP graceful shutdown procedure 4. EBGP graceful shutdown procedure
This section describes configurations and actions to be performed for This section describes configurations and actions to be performed for
the graceful shutdown of EBGP peering links. the graceful shutdown of EBGP peering links.
The goal of this procedure is to retain the paths to be shutdown The goal of this procedure is to retain the paths to be shutdown
between the peers, but with a lower LOCAL_PREF value, allowing the between the peers, but with a lower LOCAL_PREF value, allowing the
paths to remain in use while alternate paths are selected and paths to remain in use while alternate paths are selected and
propagated, rather than simply withdrawing the paths. The LOCAL_PREF propagated, rather than simply withdrawing the paths. The LOCAL_PREF
value must be lower than the one of the alternate path. 0 being the value SHOULD be lower than any of the alternative paths. The
lowest value, it can be used in all cases, except if it already has a RECOMMENDED value is 0.
special meaning within the AS.
4.1. Pre-configuration 4.1. Pre-configuration
On each ASBR supporting the graceful shutdown receiver procedure, an On each ASBR supporting the graceful shutdown receiver procedure, an
inbound BGP route policy is applied on all EBGP sessions of the ASBR, inbound BGP route policy is applied on all EBGP sessions of the ASBR,
that: that:
o matches the GRACEFUL_SHUTDOWN community. o matches the GRACEFUL_SHUTDOWN community.
o sets the LOCAL_PREF attribute of the paths tagged with the o sets the LOCAL_PREF attribute of the paths tagged with the
skipping to change at page 4, line 48 skipping to change at page 4, line 47
advertised, and tag them with the GRACEFUL_SHUTDOWN community. advertised, and tag them with the GRACEFUL_SHUTDOWN community.
o applies an inbound BGP route policy on the EBGP session to be o applies an inbound BGP route policy on the EBGP session to be
shutdown. This policy tags the paths received over the session shutdown. This policy tags the paths received over the session
with the GRACEFUL_SHUTDOWN community and sets LOCAL_PREF to a low with the GRACEFUL_SHUTDOWN community and sets LOCAL_PREF to a low
value. value.
o wait for route readvertisement over the EBGP session, and BGP o wait for route readvertisement over the EBGP session, and BGP
routing convergence on both ASBRs. routing convergence on both ASBRs.
o shutdown the EBGP session, optionally using o shutdown the EBGP session, optionally using [RFC8203] to
[I-D.ietf-idr-shutdown] to communicate the reason of the shutdown. communicate the reason of the shutdown.
In the case of a shutdown of the whole router, in addition to the In the case of a shutdown of the whole router, in addition to the
graceful shutdown of all EBGP sessions, there is a need to gracefully graceful shutdown of all EBGP sessions, there is a need to gracefully
shutdown the routes originated by this router (e.g, BGP aggregates shutdown the routes originated by this router (e.g, BGP aggregates
redistributed from other protocols, including static routes). This redistributed from other protocols, including static routes). This
can be performed by tagging these routes with the GRACEFUL_SHUTDOWN can be performed by tagging these routes with the GRACEFUL_SHUTDOWN
community and setting LOCAL_PREF to a low value. community and setting LOCAL_PREF to a low value.
4.3. BGP implementation support for graceful shutdown 4.3. BGP implementation support for graceful shutdown
skipping to change at page 5, line 40 skipping to change at page 5, line 39
The neighbor could abuse the technique and do inbound traffic The neighbor could abuse the technique and do inbound traffic
engineering by declaring some prefixes as undergoing a maintenance so engineering by declaring some prefixes as undergoing a maintenance so
as to switch traffic to another peering link. as to switch traffic to another peering link.
If this behavior is not tolerated by the ISP, it SHOULD monitor the If this behavior is not tolerated by the ISP, it SHOULD monitor the
use of the graceful shutdown community. use of the graceful shutdown community.
7. Acknowledgments 7. Acknowledgments
The authors wish to thank Olivier Bonaventure, Pradosh Mohapatra, Job The authors wish to thank Olivier Bonaventure, Pradosh Mohapatra, Job
Snijders John Heasley, and Christopher Morrow for their useful Snijders, John Heasley, and Christopher Morrow for their useful
comments. comments.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities [RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996, Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
<https://www.rfc-editor.org/info/rfc1997>. <https://www.rfc-editor.org/info/rfc1997>.
[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>.
[RFC6198] Decraene, B., Francois, P., Pelsser, C., Ahmad, Z., [RFC6198] Decraene, B., Francois, P., Pelsser, C., Ahmad, Z.,
Elizondo Armengol, A., and T. Takeda, "Requirements for Elizondo Armengol, A., and T. Takeda, "Requirements for
the Graceful Shutdown of BGP Sessions", RFC 6198, the Graceful Shutdown of BGP Sessions", RFC 6198,
DOI 10.17487/RFC6198, April 2011, DOI 10.17487/RFC6198, April 2011,
<https://www.rfc-editor.org/info/rfc6198>. <https://www.rfc-editor.org/info/rfc6198>.
[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>.
8.2. Informative References 8.2. Informative References
[I-D.ietf-idr-best-external] [I-D.ietf-idr-best-external]
Marques, P., Fernando, R., Chen, E., Mohapatra, P., and H. Marques, P., Fernando, R., Chen, E., Mohapatra, P., and H.
Gredler, "Advertisement of the best external route in Gredler, "Advertisement of the best external route in
BGP", draft-ietf-idr-best-external-05 (work in progress), BGP", draft-ietf-idr-best-external-05 (work in progress),
January 2012. January 2012.
[I-D.ietf-idr-shutdown]
Snijders, J., Heitz, J., and J. Scudder, "BGP
Administrative Shutdown Communication", draft-ietf-idr-
shutdown-10 (work in progress), June 2017.
[RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder, [RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", RFC 7911, "Advertisement of Multiple Paths in BGP", RFC 7911,
DOI 10.17487/RFC7911, July 2016, DOI 10.17487/RFC7911, July 2016,
<https://www.rfc-editor.org/info/rfc7911>. <https://www.rfc-editor.org/info/rfc7911>.
[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>.
Appendix A. Alternative techniques with limited applicability Appendix A. Alternative techniques with limited applicability
A few alternative techniques have been considered to provide graceful A few alternative techniques have been considered to provide graceful
shutdown capabilities but have been rejected due to their limited shutdown capabilities but have been rejected due to their limited
applicability. This section describe them for possible reference. applicability. This section describes them for possible reference.
A.1. Multi Exit Discriminator tweaking A.1. Multi Exit Discriminator tweaking
The MED attribute of the paths to be avoided can be increased so as The MED attribute of the paths to be avoided can be increased so as
to force the routers in the neighboring AS to select other paths. to force the routers in the neighboring AS to select other paths.
The solution only works if the alternate paths are as good as the The solution only works if the alternate paths are as good as the
initial ones with respect to the Local-Pref value and the AS Path initial ones with respect to the LOCAL_PREF value and the AS Path
Length value. In the other cases, increasing the MED value will not Length value. In the other cases, increasing the MED value will not
have an impact on the decision process of the routers in the have an impact on the decision process of the routers in the
neighboring AS. neighboring AS.
A.2. IGP distance Poisoning A.2. IGP distance Poisoning
The distance to the BGP NEXT_HOP corresponding to the maintained The distance to the BGP NEXT_HOP corresponding to the maintained
session can be increased in the IGP so that the old paths will be session can be increased in the IGP so that the old paths will be
less preferred during the application of the IGP distance tie-break less preferred during the application of the IGP distance tie-break
rule. However, this solution only works for the paths whose rule. However, this solution only works for the paths whose
alternates are as good as the old paths with respect to their Local- alternates are as good as the old paths with respect to their
Pref value, their AS Path length, and their MED value. LOCAL_PREF value, their AS Path length, and their MED value.
Also, this poisoning cannot be applied when nexthop self is used as Also, this poisoning cannot be applied when BGP NEXT_HOP self is used
there is no nexthop specific to the maintained session to poison in as there is no BGP NEXT_HOP specific to the maintained session to
the IGP. poison in the IGP.
Appendix B. Configuration Examples Appendix B. Configuration Examples
This appendix is non-normative. This appendix is non-normative.
Example routing policy configurations to honor the GRACEFUL_SHUTDOWN Example routing policy configurations to honor the GRACEFUL_SHUTDOWN
well-known BGP community. well-known BGP community.
B.1. Cisco IOS XR B.1. Cisco IOS XR
skipping to change at page 9, line 13 skipping to change at page 9, line 13
following the injection of new best paths within the IBGP topology. following the injection of new best paths within the IBGP topology.
C.2.1. Unreachability local to the ASBR C.2.1. Unreachability local to the ASBR
An ASBR that selects as best a path received over a newly established An ASBR that selects as best a path received over a newly established
EBGP session may transiently drop traffic. This can typically happen EBGP session may transiently drop traffic. This can typically happen
when the NEXT_HOP attribute differs from the IP address of the EBGP when the NEXT_HOP attribute differs from the IP address of the EBGP
peer, and the receiving ASBR has not yet resolved the MAC address peer, and the receiving ASBR has not yet resolved the MAC address
associated with the IP address of that "third party" NEXT_HOP. associated with the IP address of that "third party" NEXT_HOP.
A BGP speaker implementation may avoid such losses by ensuring that A BGP speaker implementation MAY avoid such losses by ensuring that
"third party" NEXT_HOPs are resolved before installing paths using "third party" NEXT_HOPs are resolved before installing paths using
these in the RIB. these in the RIB.
Alternatively, the operator (script) may ping third party NEXT_HOPs Alternatively, the operator (script) MAY ping third party NEXT_HOPs
that are expected to be used before establishing the session. By that are expected to be used before establishing the session. By
proceeding like this, the MAC addresses associated with these third proceeding like this, the MAC addresses associated with these third
party NEXT_HOPs are resolved by the startup initiator. party NEXT_HOPs are resolved by the startup initiator.
C.2.2. IBGP convergence C.2.2. IBGP convergence
During the establishment of an EBGP session, in some corner cases a During the establishment of an EBGP session, in some corner cases a
router may have no path toward an affected prefix, leading to loss of router may have no path toward an affected prefix, leading to loss of
connectivity. connectivity.
A typical example for such transient unreachability for a given A typical example for such transient unreachability for a given
prefix is the following: prefix is the following:
Let's consider 3 route reflectors RR1, RR2, RR3. There is a full Let's consider three Route Reflectors (RR): RR1, RR2, RR3. There is
mesh of IBGP sessions between them. a full mesh of IBGP sessions between them.
1. RR1 is initially advertising the current best path to the 1. RR1 is initially advertising the current best path to the
members of its IBGP RR full-mesh. It propagated that path within members of its IBGP RR full-mesh. It propagated that path within
its RR full-mesh. RR2 knows only that path toward the prefix. its RR full-mesh. RR2 knows only that path toward the prefix.
2. RR3 receives a new best path originated by the startup 2. RR3 receives a new best path originated by the startup
initiator, being one of its RR clients. RR3 selects it as best, initiator, being one of its RR clients. RR3 selects it as best,
and propagates an UPDATE within its RR full-mesh, i.e., to RR1 and and propagates an UPDATE within its RR full-mesh, i.e., to RR1 and
RR2. RR2.
 End of changes. 21 change blocks. 
40 lines changed or deleted 38 lines changed or added

This html diff was produced by rfcdiff 1.45. The latest version is available from http://tools.ietf.org/tools/rfcdiff/