wdiff draft-ietf-grow-bgp-gshut-10.txt draft-ietf-grow-bgp-gshut-11.txt

Network Working Group P. Francois, Ed.
Internet-Draft Individual Contributor
Intended status: Informational B. Decraene, Ed.
Expires: January 28, March 24, 2018 Orange
C. Pelsser
Strasbourg University
K. Patel
Arrcus, Inc.
C. Filsfils
Cisco Systems
July 27,
September 20, 2017

Graceful BGP session shutdown
draft-ietf-grow-bgp-gshut-10
draft-ietf-grow-bgp-gshut-11

Abstract

This draft standardizes a new well-known BGP community
GRACEFUL_SHUTDOWN to signal the graceful shutdown of paths. This
draft also describes operational procedures aimed at reducing which use this community
to reduce the amount of traffic lost during planned maintenances of routers or
links, involving the shutdown of when BGP peering sessions. It defines a
well-known BGP community, called GRACEFUL_SHUTDOWN, sessions are
about to signal the
graceful shutdown of paths. be shut down deliberately, e.g. for planned maintenance.

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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This Internet-Draft will expire on January 28, March 24, 2018.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Packet loss upon manual EBGP session shutdown . . . . . . . . 4 3
4. Practices to avoid packet losses . . . . . . . . . . . . . . 4
4.1. Improving availability of alternate paths . . . . . . . . 4
4.2. Make before break convergence: graceful shutdown . . . . 5
4.3. Forwarding modes and transient forwarding loops during
convergence . . . . . . . . . . . . . . . . . . . . . . . 5
5. EBGP graceful shutdown procedure . . . . . . . . . . . . . . 5
5.1. 4
4.1. Pre-configuration . . . . . . . . . . . . . . . . . . . . 5
5.2. 4
4.2. Operations at maintenance time . . . . . . . . . . . . . 6
5.3. 4
4.3. BGP implementation support for graceful shutdown . . . . 6
6. Beyond EBGP graceful shutdown . . . . . . . . . . . . . . . . 7
6.1. IBGP graceful shutdown . . . . . . . . . . . . . . . . . 7
6.2. EBGP session establishment . . . . . . . . . . . . . . . 7
7. 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. 5
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
10. 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. 5
8.2. Informative References . . . . . . . . . . . . . . . . . 9 6
Appendix A. Alternative techniques with limited applicability . 10 6
A.1. Multi Exit Discriminator tweaking . . . . . . . . . . . . 10 6
A.2. IGP distance Poisoning . . . . . . . . . . . . . . . . . 10 7
Appendix B. Configuration Examples . . . . . . . . . . . . . . . 10 7
B.1. Cisco IOS XR . . . . . . . . . . . . . . . . . . . . . . 11 7
B.2. BIRD . . . . . . . . . . . . . . . . . . . . . . . . . . 11 8
B.3. OpenBGPD . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses 8
Appendix C. Beyond EBGP graceful shutdown . . . . . . . . . . . 8
C.1. IBGP graceful shutdown . . . . . . . . . . . . 12

1. Introduction

Routing changes in BGP can be caused by planned maintenance
operations. . . . . . 8
C.2. EBGP session establishment . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10

1. Introduction

Routing changes in BGP can be caused by planned maintenance
operations. This document defines a well-known community [RFC1997],
called GRACEFUL_SHUTDOWN, for the purpose of reducing the management
overhead of gracefully shutting down BGP sessions. The well-known
community allows implementers to provide an automated graceful
shutdown mechanism that does not require any router reconfiguration
at maintenance time.

This document discusses operational procedures to be applied in order
to reduce or eliminate loss of packets during the a maintenance. These losses come Loss
comes from the transient lack of reachability during the BGP convergence following
which follows the shutdown of an EBGP peering session between two
Autonomous System Border Routers (ASBR).

This document presents procedures for the cases where the forwarding
plane is impacted by the maintenance, hence when the use of Graceful
Restart does not apply.

The procedures described in this document can be applied to reduce or
avoid packet loss for outbound and inbound traffic flows initially
forwarded along the peering link to be shut down. These procedures
trigger, in both ASes, rerouting to the alternate path paths if one exists they exist
within the AS, while allowing the use of the old path until alternate
ones are learned. This ensures that routers always have a valid
route available during the convergence process.

The goal of the document is to meet the requirements described in
[RFC6198] at best, without changing the BGP protocol.

This document defines a well-known community [RFC1997], called
GRACEFUL_SHUTDOWN, for the purpose of reducing the management
overhead of gracefully shutting down BGP sessions. The well-known
community allows implementers to provide an automated graceful
shutdown mechanism that does not require any router reconfiguration
at maintenance time.

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].

2. Terminology

graceful shutdown initiator: a router on which the session shutdown
is performed for the maintenance.

graceful shutdown receiver: a router that has a BGP session, to be
shutdown, with the graceful shutdown initiator.

Initiator AS: the Autonomous System of the graceful shutdown
initiator.

Receiver AS: the Autonomous System of the graceful shutdown receiver.

Loss of Connectivity (LoC: the state when a router has no path toward
an affected prefix.

3. Packet loss upon manual EBGP session shutdown

Packets can be lost during the BGP convergence following a manual
shutdown of an EBGP session for two reasons.

First, some routers involved in the convergence process can transiently
lack paths have no path toward an affected prefix, and
drop traffic destined to this prefix. This is because alternate
paths can be hidden by nodes of an AS. This happens when [RFC7911]
is not used and the paths are not selected as best by the ASBR that
receive them on an EBGP session, or by Route Reflectors that do not
propagate them further in the IBGP topology because they do not
select them as best.

Second, within the AS, the FIB of routers can be transiently inconsistent during between routers within the BGP convergence AS,
and packets toward affected prefixes can loop and be dropped. Note that these loops only happen
when ASBR-to-ASBR dropped unless
encapsulation is not used within the AS.

This document only addresses the first reason.

4. Practices to avoid packet losses EBGP graceful shutdown procedure

This section describes means for an ISP configurations and actions to reduce the transient loss
of packets upon a manual shutdown of a BGP session.

4.1. Improving availability of alternate paths

All solutions that increase the availability of alternate BGP paths
at routers performing forwarding lookups from BGP routes such as
[I-D.ietf-idr-best-external] and [RFC7911] help in reducing the LoC
bound with the shutdown of EBGP sessions.

Any such solution where, at any single step of the convergence
process following the EBGP session shutdown, a BGP router does not
receive a message withdrawing the only path it currently knows for a
given NLRI, allows for a simplified graceful shutdown procedure.

Note that the LoC for the inbound traffic of graceful shutdown
initiator, due to the lack of an alternate path on be performed for
the graceful shutdown receiver is not under the control of the Initiator AS. The
part of the procedure aimed at avoiding LoC for incoming traffic
should thus be applied even if no LoC are expected for the outgoing
traffic.

4.2. Make before break convergence: graceful shutdown EBGP peering links.

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
paths to remain in use while alternate paths are selected and
propagated, rather than simply withdrawing the paths. The LOCAL_PREF
value must be lower than the one of the alternate path. 0 being the
lowest value, it can be used in all cases, except if it already has a
special meaning within the AS.

Section 5 describes configurations and actions to be performed for
the graceful shutdown of BGP sessions.

4.3. Forwarding modes and transient forwarding loops during convergence

The graceful shutdown procedure or the solutions improving the
availability of alternate paths, do not change the fact that BGP
convergence and the subsequent FIB updates are run independently on
each router of the ASes. If the AS applying the solution does not
rely on encapsulation to forward packets from the Ingress Border
Router to the Egress Border Router, then transient forwarding loops
and consequent packet losses can occur during the convergence
process. If zero LoC is required, encapsulation is required between
ASBRs of the AS.

5. EBGP graceful shutdown procedure

This section describes configurations and actions to be performed for
the graceful shutdown of EBGP peering links.

5.1.

4.1. Pre-configuration

On each ASBR supporting the graceful shutdown receiver procedure, an
inbound BGP route policy is applied on all EBGP sessions of the ASBR,
that:

o matches the GRACEFUL_SHUTDOWN community community.

o sets the LOCAL_PREF attribute of the paths tagged with the
GRACEFUL_SHUTDOWN community to a low value

Note that in value.

4.2. Operations at maintenance time

On the case where an AS is aggregating multiple routes
under a covering prefix, it is recommended to filter out the
GRACEFUL_SHUTDOWN community from the resulting aggregate BGP route.
By doing so, the setting of the GRACEFUL_SHUTDOWN community on one of
the aggregated routes will not let the entire aggregate inherit the
community. Not doing so would let the entire aggregate undergo the
graceful shutdown behavior.

5.2. Operations at maintenance time

On the graceful shutdown initiator, upon maintenance time, it is
required to:

o apply graceful shutdown initiator, at maintenance time, the
operator:

o applies an outbound BGP route policy on the EBGP session to be
shutdown. This policy tags the paths propagated over the session
with the GRACEFUL_SHUTDOWN community. This will trigger the BGP
implementation to re-advertise all active routes previously
advertised, and tag them with the GRACEFUL_SHUTDOWN community.

o apply applies an inbound BGP route policy on the EBGP session to be
shutdown. This policy tags the paths received over the session
with the GRACEFUL_SHUTDOWN community and sets LOCAL_PREF to a low
value.

o wait for route readvertisement over the EBGP session, and BGP
routing convergence to happen. on both ASBRs.

o shutdown the EBGP session, optionally using
[I-D.ietf-idr-shutdown] to communicate the reason of the shutdown.

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 graceful gracefully
shutdown the routes originated by this router (e.g, BGP aggregates
redistributed from other protocols, including static routes). This
can be performed by tagging such these routes with the GRACEFUL_SHUTDOWN
community and setting LOCAL_PREF to a low value.

5.3.

4.3. BGP implementation support for graceful shutdown

BGP router implementation MAY Implementers SHOULD provide features aimed at automating
the application of the graceful shutdown procedures described above.

Upon a session shutdown specified as graceful by configuration knobs that utilize the operator, a
GRACEFUL_SHUTDOWN community to drain BGP
implementation supporting a graceful shutdown feature SHOULD:

1. Update all the paths propagated over neighbors in preparation of
impending neighbor shutdown. Implementation details are outside the corresponding EBGP
session, tagging
scope of this document.

5. IANA Considerations

The IANA has assigned the GRACEFUL_SHUTDOWN community value 0xFFFF0000 to them. Any
subsequent update sent over the session being gracefully planned-
shut
down SHOULD be tagged with community in the "BGP Well-known Communities" registry. IANA is
requested to change the name planned-shut to GRACEFUL_SHUTDOWN community.

2. Lower and
set this document as the reference.

6. Security Considerations

By providing the graceful shutdown service to a neighboring AS, an
ISP provides means to this neighbor and possibly its downstream ASes
to lower the LOCAL_PREF value of assigned to the paths received over from
this neighbor.

The neighbor could abuse the EBGP
session being shut down technique and set the GRACEFUL_SHUTDOWN community.

3. Optionally shut down the session after a configured time.

4. Prevent the GRACEFUL_SHUTDOWN community from being inherited do inbound traffic
engineering by a
path that would aggregate declaring some paths tagged with the GSHUT
community. This behavior avoids the GSHUT procedure prefixes as undergoing a maintenance so
as to be
applied switch traffic to another peering link.

If this behavior is not tolerated by the aggregate upon the graceful shutdown of one ISP, it SHOULD monitor the
use of its
covered prefixes.

A BGP implementation supporting a the graceful shutdown feature SHOULD
also automatically install the BGP policies that are supposed community.

7. Acknowledgments

The authors wish to be
configured, as described in Section 5.1 thank Olivier Bonaventure, Pradosh Mohapatra, Job
Snijders John Heasley, and Christopher Morrow for sessions over which
graceful shutdown is their useful
comments.

8. References

8.1. Normative References

[RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
<https://www.rfc-editor.org/info/rfc1997>.

[RFC2119] Bradner, S., "Key words for use in RFCs to be supported.

6. Beyond EBGP graceful shutdown

6.1. IBGP graceful shutdown

For the shutdown of an IBGP session, provided the IBGP topology is
viable after 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.,
Elizondo Armengol, A., and T. Takeda, "Requirements for
the maintenance Graceful Shutdown of the session, i.e, if all BGP speakers Sessions", RFC 6198,
DOI 10.17487/RFC6198, April 2011,
<https://www.rfc-editor.org/info/rfc6198>.

8.2. Informative References

[I-D.ietf-idr-best-external]
Marques, P., Fernando, R., Chen, E., Mohapatra, P., and H.
Gredler, "Advertisement of the AS best external route in
BGP", draft-ietf-idr-best-external-05 (work in progress),
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,
"Advertisement of Multiple Paths in BGP", RFC 7911,
DOI 10.17487/RFC7911, July 2016,
<https://www.rfc-editor.org/info/rfc7911>.

Appendix A. Alternative techniques with limited applicability

A few alternative techniques have an IBGP signaling path for all prefixes advertised on
this been considered to provide graceful
shutdown IBGP session, then the shutdown of an IBGP
session does not lead capabilities but have been rejected due to transient unreachability. As a consequence,
no specific graceful shutdown action is required.

6.2. EBGP session establishment

We identify two potential causes their limited
applicability. This section describe them for transient packet losses upon the
establishment of an EBGP session. possible reference.

A.1. Multi Exit Discriminator tweaking

The first one is local MED attribute of the paths to be avoided can be increased so as
to force the
startup initiator, routers in the second one is due neighboring AS to select other paths.

The solution only works if the BGP convergence
following the injection of new best alternate paths within are as good as the IBGP topology.

6.2.1. Unreachability local
initial ones with respect to the ASBR

An ASBR that selects as best a path received over a newly established
EBGP session may transiently drop traffic. This can typically happen
when the NEXT_HOP attribute differs from Local-Pref value and the IP address of AS Path
Length value. In the EBGP
peer, and other cases, increasing the receiving ASBR has MED value will not yet resolved the MAC address
associated with
have an impact on the IP address decision process of that "third party" NEXT_HOP.

A BGP speaker implementation may avoid such losses by ensuring that
"third party" NEXT_HOPs are resolved before installing paths using
these the routers in the RIB.

Alternatively,
neighboring AS.

A.2. IGP distance Poisoning

The distance to the operator (script) may ping third party NEXT_HOPs
that are expected BGP NEXT_HOP corresponding to the maintained
session can be used before establishing increased in the session. By
proceeding like this, IGP so that the MAC addresses associated with these third
party NEXT_HOPs are resolved by the startup initiator.

6.2.2. IBGP convergence

Corner cases leading to LoC can occur old paths will be
less preferred during the establishment of an
EBGP session.

A typical example for such transient unreachability for a given
prefix is the following:

Let's consider 3 route reflectors RR1, RR2, RR3. There is a full
mesh application of IBGP sessions between them.

1. RR1 is initially advertising the current best path to the
members of its IBGP RR full-mesh. It propagated that path within
its RR full-mesh. RR2 knows IGP distance tie-break
rule. However, this solution only that path toward the prefix.

2. RR3 receives a new best path originated by works for the startup
initiator, being one of its RR clients. RR3 selects it paths whose
alternates are as best,
and propagates an UPDATE within its RR full-mesh, i.e., good as the old paths with respect to RR1 and
RR2.

3. RR1 receives that path, reruns its decision process, their Local-
Pref value, their AS Path length, and picks their MED value.

Also, this new path poisoning cannot be applied when nexthop self is used as best. As a result, RR1 withdraws its previously
announced best-path on the IBGP sessions of its RR full-mesh.

4. If, for any reason, RR3 processes the withdraw generated in
step 3, before processing
there is no nexthop specific to the update generated maintained session to poison in step 2, RR3
transiently suffers from unreachability for the affected prefix.

The use of [I-D.ietf-idr-best-external] among
the RR of IGP.

Appendix B. Configuration Examples

This appendix is non-normative.

Example routing policy configurations to honor the IBGP
full-mesh can solve these corner cases by ensuring that within an AS, GRACEFUL_SHUTDOWN
well-known BGP community.

B.1. Cisco IOS XR

community-set comm-graceful-shutdown
65535:0
end-set
!
route-policy AS64497-ebgp-inbound
! normally this policy would contain much more
if community matches-any comm-graceful-shutdown then
set local-preference 0
endif
end-policy
!
router bgp 64496
neighbor 2001:db8:1:2::1
remote-as 64497
address-family ipv6 unicast
send-community-ebgp
route-policy AS64497-ebgp-inbound in

!
!
!

B.2. BIRD

B.3. OpenBGPD

AS 64496
router-id 192.0.2.1
neighbor 2001:db8:1:2::1 {
remote-as 64497
}
# normally this policy would contain much more
match from any community GRACEFUL_SHUTDOWN set { localpref 0 }

Appendix C. Beyond EBGP graceful shutdown

C.1. IBGP graceful shutdown

For the advertisement shutdown of a new route an IBGP session, provided the IBGP topology is not translated into
viable after the withdraw maintenance of a former route.

Indeed, "best-external" ensures that an ASBR does not withdraw a
previously advertised (EBGP) path when it receives the session, i.e, if all BGP speakers
of the AS have an additional,
preferred IBGP signaling path over for all prefixes advertised on
this graceful shutdown IBGP session, then the shutdown of an IBGP session. Also, "best-intra-cluster"
ensures that a RR
session does not withdraw a previously advertised (IBGP)
path lead to its non clients (e.g. other RRs in a mesh of RR) when it
receives transient unreachability. As a new, preferred path over consequence,
no specific graceful shutdown action is required.

C.2. EBGP session establishment

We identify two potential causes for transient packet losses upon the
establishment of an IBGP EBGP session.

7. IANA Considerations The IANA has assigned the community value 0xFFFF0000 first one is local to the planned-
shut community in
startup initiator, the "BGP Well-known Communities" registry. IANA second one is
requested to change the name planned-shut due to GRACEFUL_SHUTDOWN and
set this document as the reference.

8. Security Considerations

By providing BGP convergence
following the graceful shutdown service to a neighboring AS, an
ISP provides means to this neighbor and possibly its downstream ASes
to lower injection of new best paths within the LOCAL_PREF value assigned IBGP topology.

C.2.1. Unreachability local to the paths ASBR

An ASBR that selects as best a path received over a newly established
EBGP session may transiently drop traffic. This can typically happen
when the NEXT_HOP attribute differs from
this neighbor.

The neighbor could abuse the technique IP address of the EBGP
peer, and do inbound traffic
engineering by declaring some prefixes as undergoing a maintenance so
as to switch traffic to another peering link.

If this behavior is the receiving ASBR has not tolerated by yet resolved the ISP, it SHOULD monitor MAC address
associated with the
use IP address of that "third party" NEXT_HOP.

A BGP speaker implementation may avoid such losses by ensuring that
"third party" NEXT_HOPs are resolved before installing paths using
these in the graceful shutdown community.

9. Acknowledgments

The authors wish RIB.

Alternatively, the operator (script) may ping third party NEXT_HOPs
that are expected to thank Olivier Bonaventure, Pradosh Mohapatra, Job
Snijders and John Heasley for their useful comments.

10. References

10.1. Normative References

[RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
<http://www.rfc-editor.org/info/rfc1997>.

[RFC2119] Bradner, S., "Key words for use be used before establishing the session. By
proceeding like this, the MAC addresses associated with these third
party NEXT_HOPs are resolved by the startup initiator.

C.2.2. IBGP convergence

During the establishment of an EBGP session, in RFCs some corner cases a
router may have no path toward an affected prefix, leading to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC6198] Decraene, B., Francois, P., Pelsser, C., Ahmad, Z.,
Elizondo Armengol, A., and T. Takeda, "Requirements loss of
connectivity.

A typical example for such transient unreachability for a given
prefix is the Graceful Shutdown following:

Let's consider 3 route reflectors RR1, RR2, RR3. There is a full
mesh of BGP Sessions", RFC 6198,
DOI 10.17487/RFC6198, April 2011,
<http://www.rfc-editor.org/info/rfc6198>.

10.2. Informative References

[I-D.ietf-idr-best-external]
Marques, P., Fernando, R., Chen, E., Mohapatra, P., and H.
Gredler, "Advertisement IBGP sessions between them.

1. RR1 is initially advertising the current best path to the
members of its IBGP RR full-mesh. It propagated that path within
its RR full-mesh. RR2 knows only that path toward the prefix.

2. RR3 receives a new best external route in
BGP", draft-ietf-idr-best-external-05 (work in progress),
January 2012.

[I-D.ietf-idr-shutdown]
Snijders, J., Heitz, J., path originated by the startup
initiator, being one of its RR clients. RR3 selects it as best,
and J. Scudder, "BGP
Administrative Shutdown Communication", draft-ietf-idr-
shutdown-10 (work in progress), June 2017.

[RFC7911] Walton, D., Retana, A., Chen, E., propagates an UPDATE within its RR full-mesh, i.e., to RR1 and J. Scudder,
"Advertisement of Multiple Paths in BGP", RFC 7911,
DOI 10.17487/RFC7911, July 2016,
<http://www.rfc-editor.org/info/rfc7911>.

Appendix A. Alternative techniques with limited applicability

A few alternative techniques have been considered to provide graceful
shutdown capabilities but have been rejected due to their limited
applicability. This section describe them for possible reference.

A.1. Multi Exit Discriminator tweaking

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.

The solution only works if the alternate paths are as good as the
initial ones with respect to the Local-Pref value
RR2.

3. RR1 receives that path, reruns its decision process, and the AS Path
Length value. In the other cases, increasing the MED value will not
have an impact picks
this new path as best. As a result, RR1 withdraws its previously
announced best-path on the decision process IBGP sessions of its RR full-mesh.

4. If, for any reason, RR3 processes the routers withdraw generated in
step 3, before processing the
neighboring AS.

A.2. IGP distance Poisoning update generated in step 2, RR3
transiently suffers from unreachability for the affected prefix.

The distance to use of [RFC7911] or [I-D.ietf-idr-best-external] among the BGP NEXT_HOP corresponding to RR of
the maintained
session IBGP full-mesh can be increased in the IGP so solve these corner cases by ensuring that
within an AS, the old paths will be
less preferred during the application advertisement of the IGP distance tie-break
rule. However, this solution only works for the paths whose
alternates are as good as the old paths with respect to their Local-
Pref value, their AS Path length, and their MED value.

Also, this poisoning cannot be applied when nexthop self is used as
there a new route is no nexthop specific to the maintained session to poison in not translated into
the IGP.

Appendix B. Configuration Examples

This appendix is non-normative.

Example routing policy configurations withdraw of a former route.

Indeed, "best-external" ensures that an ASBR does not withdraw a
previously advertised (EBGP) path when it receives an additional,
preferred path over an IBGP session. Also, "best-intra-cluster"
ensures that a RR does not withdraw a previously advertised (IBGP)
path to honor the GRACEFUL_SHUTDOWN
well-known BGP community.

B.1. Cisco IOS XR

!
!
!

B.2. BIRD

B.3. OpenBGPD
AS 64496
router-id 192.0.2.1
neighbor 2001:db8:1:2::1 {
remote-as 64497
}
# normally this policy would contain much more
match from any community GRACEFUL_SHUTDOWN set { localpref 0 } a mesh of RR) when it
receives a new, preferred path over an IBGP session.

Authors' Addresses

Pierre Francois (editor)
Individual Contributor

Email: pfrpfr@gmail.com

Bruno Decraene (editor)
Orange

Email: bruno.decraene@orange.com

Cristel Pelsser
Strasbourg University

Email: pelsser@unistra.fr

Keyur Patel
Arrcus, Inc.

Email: keyur@arrcus.com

Clarence Filsfils
Cisco Systems

Email: cfilsfil@cisco.com