--- 1/draft-ietf-grow-bgp-gshut-11.txt 2017-10-12 06:13:48.834472117 -0700 +++ 2/draft-ietf-grow-bgp-gshut-12.txt 2017-10-12 06:13:48.854472571 -0700 @@ -1,25 +1,25 @@ Network Working Group P. Francois, Ed. Internet-Draft Individual Contributor Intended status: Informational B. Decraene, Ed. -Expires: March 24, 2018 Orange +Expires: April 14, 2018 Orange C. Pelsser Strasbourg University K. Patel Arrcus, Inc. C. Filsfils Cisco Systems - September 20, 2017 + October 11, 2017 Graceful BGP session shutdown - draft-ietf-grow-bgp-gshut-11 + draft-ietf-grow-bgp-gshut-12 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 which use this community to reduce the amount of traffic lost when BGP peering sessions are about to be shut down deliberately, e.g. for planned maintenance. Status of This Memo @@ -30,21 +30,21 @@ 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 https://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 March 24, 2018. + This Internet-Draft will expire on April 14, 2018. 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 (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -85,43 +85,43 @@ 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 a maintenance. Loss - comes from transient lack of reachability during BGP convergence - which follows the shutdown of an EBGP peering session between two - Autonomous System Border Routers (ASBR). + to reduce or eliminate loss of packets during a maintenance + operation. Loss comes from transient lack of reachability during BGP + convergence 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 alternate paths if 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. + trigger, in both Autonomous Sytems (AS), rerouting to alternate paths + if 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. 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]. + document are to be interpreted as described in RFC 8174 [RFC8174]. 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. 3. Packet loss upon manual EBGP session shutdown @@ -145,23 +145,22 @@ 4. EBGP graceful shutdown procedure This section describes configurations and actions to be performed for the graceful shutdown of 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. + value SHOULD be lower than any of the alternative paths. The + RECOMMENDED value is 0. 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. o sets the LOCAL_PREF attribute of the paths tagged with the @@ -179,22 +178,22 @@ advertised, and tag them with the GRACEFUL_SHUTDOWN community. o 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 on both ASBRs. - o shutdown the EBGP session, optionally using - [I-D.ietf-idr-shutdown] to communicate the reason of the shutdown. + o shutdown the EBGP session, optionally using [RFC8203] 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 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 these routes with the GRACEFUL_SHUTDOWN community and setting LOCAL_PREF to a low value. 4.3. BGP implementation support for graceful shutdown @@ -220,89 +219,88 @@ The neighbor could abuse the technique 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 not tolerated by the ISP, it SHOULD monitor the use of the graceful shutdown community. 7. Acknowledgments 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. 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, . - [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate - Requirement Levels", BCP 14, RFC 2119, - DOI 10.17487/RFC2119, March 1997, - . - [RFC6198] Decraene, B., Francois, P., Pelsser, C., Ahmad, Z., Elizondo Armengol, A., and T. Takeda, "Requirements for the Graceful Shutdown of BGP Sessions", RFC 6198, DOI 10.17487/RFC6198, April 2011, . + [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC + 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, + May 2017, . + 8.2. Informative References [I-D.ietf-idr-best-external] Marques, P., Fernando, R., Chen, E., Mohapatra, P., and H. Gredler, "Advertisement of the 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, . + [RFC8203] Snijders, J., Heitz, J., and J. Scudder, "BGP + Administrative Shutdown Communication", RFC 8203, + DOI 10.17487/RFC8203, July 2017, + . + 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. + applicability. This section describes 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 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 have an impact on the decision process of the routers in the neighboring AS. A.2. IGP distance Poisoning 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 less preferred during the application 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. + 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 is no nexthop specific to the maintained session to poison in - the IGP. + Also, this poisoning cannot be applied when BGP NEXT_HOP self is used + as there is no BGP NEXT_HOP specific to the maintained session to + poison in the IGP. Appendix B. Configuration Examples This appendix is non-normative. Example routing policy configurations to honor the GRACEFUL_SHUTDOWN well-known BGP community. B.1. Cisco IOS XR @@ -376,40 +374,40 @@ following the injection of new best paths within the IBGP topology. C.2.1. Unreachability local 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 the IP address of the EBGP peer, and the receiving ASBR has not yet resolved the MAC address 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 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 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 some corner cases a router may have no path toward an affected prefix, leading to loss of connectivity. 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 of IBGP sessions between them. + Let's consider three Route Reflectors (RR): RR1, RR2, RR3. There is + a full mesh 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 only that path toward the prefix. 2. RR3 receives a new best path originated by the startup 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 RR2.