--- 1/draft-ietf-grow-bgp-gshut-06.txt 2017-06-22 03:13:08.733392213 -0700 +++ 2/draft-ietf-grow-bgp-gshut-07.txt 2017-06-22 03:13:08.757392787 -0700 @@ -1,101 +1,88 @@ Network Working Group Pierre Francois -Internet-Draft Institute IMDEA Networks -Intended status: Informational Bruno Decraene -Expires: February 15, 2015 Orange - Cristel Pelsser - Internet Initiative Japan - Keyur Patel - Clarence Filsfils +Internet-Draft Individual Contributor +Intended status: Informational B. Decraene +Expires: December 23, 2017 Orange + C. Pelsser + Strasbourg University + K. Patel + Arrcus, Inc. + C. Filsfils Cisco Systems - August 14, 2014 + June 21, 2017 Graceful BGP session shutdown - draft-ietf-grow-bgp-gshut-06 + draft-ietf-grow-bgp-gshut-07 Abstract This draft describes operational procedures aimed at reducing the amount of traffic lost during planned maintenances of routers or links, involving the shutdown of BGP peering sessions. -Status of this Memo +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 working documents as Internet-Drafts. The list of current Internet- Drafts is at http://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 February 15, 2015. + This Internet-Draft will expire on December 23, 2017. Copyright Notice - Copyright (c) 2014 IETF Trust and the persons identified as the + 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 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. - This document may contain material from IETF Documents or IETF - Contributions published or made publicly available before November - 10, 2008. The person(s) controlling the copyright in some of this - material may not have granted the IETF Trust the right to allow - modifications of such material outside the IETF Standards Process. - Without obtaining an adequate license from the person(s) controlling - the copyright in such materials, this document may not be modified - outside the IETF Standards Process, and derivative works of it may - not be created outside the IETF Standards Process, except to format - it for publication as an RFC or to translate it into languages other - than English. - Table of Contents - 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 3. Packet loss upon manual eBGP session shutdown . . . . . . . . 5 - 4. Practices to avoid packet losses . . . . . . . . . . . . . . . 5 - 4.1. Improving availability of alternate paths . . . . . . . . 5 - 4.2. Make before break convergence: g-shut . . . . . . . . . . 6 - 4.2.1. eBGP g-shut . . . . . . . . . . . . . . . . . . . . . 6 - 4.2.2. iBGP g-shut . . . . . . . . . . . . . . . . . . . . . 7 - 4.2.3. Router g-shut . . . . . . . . . . . . . . . . . . . . 7 + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 + 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 + 3. Packet loss upon manual eBGP session shutdown . . . . . . . . 3 + 4. Practices to avoid packet losses . . . . . . . . . . . . . . 4 + 4.1. Improving availability of alternate paths . . . . . . . . 4 + 4.2. Make before break convergence: g-shut . . . . . . . . . . 4 5. Forwarding modes and transient forwarding loops during - convergence . . . . . . . . . . . . . . . . . . . . . . . . . 8 - 6. Link Up cases . . . . . . . . . . . . . . . . . . . . . . . . 8 - 6.1. Unreachability local to the ASBR . . . . . . . . . . . . . 8 - 6.2. iBGP convergence . . . . . . . . . . . . . . . . . . . . . 9 - 7. IANA assigned g-shut BGP community . . . . . . . . . . . . . . 9 - 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 - 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 10.1. Normative References . . . . . . . . . . . . . . . . . . . 10 - 10.2. Informative References . . . . . . . . . . . . . . . . . . 11 - Appendix A. Alternative techniques with limited applicability . . 11 - A.1. Multi Exit Discriminator tweaking . . . . . . . . . . . . 11 - A.2. IGP distance Poisoning . . . . . . . . . . . . . . . . . . 11 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 + convergence . . . . . . . . . . . . . . . . . . . . . . . . . 7 + 6. Link Up cases . . . . . . . . . . . . . . . . . . . . . . . . 7 + 6.1. Unreachability local to the ASBR . . . . . . . . . . . . 7 + 6.2. iBGP convergence . . . . . . . . . . . . . . . . . . . . 7 + 7. IANA assigned g-shut BGP community . . . . . . . . . . . . . 8 + 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 + 9. Security Considerations . . . . . . . . . . . . . . . . . . . 9 + 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 + 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 + 11.1. Normative References . . . . . . . . . . . . . . . . . . 9 + 11.2. Informative References . . . . . . . . . . . . . . . . . 9 + Appendix A. Alternative techniques with limited applicability . 10 + A.1. Multi Exit Discriminator tweaking . . . . . . . . . . . . 10 + A.2. IGP distance Poisoning . . . . . . . . . . . . . . . . . 10 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction Routing changes in BGP can be caused by planned, maintenance operations. This document discusses operational procedures to be applied in order to reduce or eliminate losses of packets during the maintenance. These losses come from the transient lack of reachability during the BGP convergence following the shutdown of an eBGP peering session between two Autonomous System Border Routers (ASBR). @@ -107,21 +94,21 @@ 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 involved ASes, rerouting to the alternate path, while allowing routers to keep using old paths until alternate ones are learned, installed in the RIB and in the FIB. 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 - [REQS] at best, without changing the BGP protocol. + [RFC6198] at best, without changing the BGP protocol. Still, it explains why reserving a community value for the purpose of BGP session graceful shutdown would reduce the management overhead bound with the solution. It would also allow vendors to provide an automatic 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]. @@ -163,62 +150,70 @@ 4. Practices to avoid packet losses This section describes means for an ISP 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 packet lookups in BGP tables such as - [BestExternal] and [AddPath] help in reducing the LoC bound with - manual shutdown of eBGP sessions. + [I-D.ietf-idr-best-external] and [RFC7911] help in reducing the LoC + bound with manual shutdown of eBGP sessions. One of such solutions increasing diversity in such a way that, 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 g-shut procedure. Note that the LoC for the inbound traffic of the maintained router, induced by a lack of alternate path propagation within the iBGP topology of a neighboring AS is not under the control of the operator performing the maintenance. The part of the procedure aimed at avoiding LoC for incoming paths can thus be applied even if no LoC are expected for the outgoing paths. 4.2. Make before break convergence: g-shut This section describes configurations and actions to be performed for - the graceful shutdown of eBGP peering links. + the graceful shutdown of eBGP sessions, iBGP sessions or a whole BGP + speaker. - The goal of this procedure is to let the paths being shutdown - visible, but with a lower LOCAL_PREF value, while alternate paths - spread through the iBGP topology. Instead of withdrawing the path, - routers of an AS will keep on using it until they become aware of - alternate paths. + The goal of this procedure is to let, in both ASes, the paths being + shutdown visible, but with a lower LOCAL_PREF value, while alternate + paths spread through the iBGP topology. Instead of withdrawing the + path, routers of an AS will keep on using it until they become aware + of alternate paths. 4.2.1. eBGP g-shut + This section describes configurations and actions to be performed for + the graceful shutdown of eBGP peering links. + 4.2.1.1. Pre-configuration On each ASBR supporting the g-shut procedure, an outbound BGP route policy is applied on all iBGP sessions of the ASBR, that: + o matches the g-shut community - o sets the LOCAL_PREF attribute of the paths tagged with the - g-shut community to a low value + + o sets the LOCAL_PREF attribute of the paths tagged with the g-shut + community to a low value + o removes the g-shut community from the paths. - o optionally, adds an AS specific g-shut community on these paths - to indicate that these are to be withdrawn soon. If some - ingress ASBRs reset the LOCAL_PREF attribute, this AS specific - g-shut community will be used to override other LOCAL_PREF - preference changes. + + o optionally, adds an AS specific g-shut community on these paths to + indicate that these are to be withdrawn soon. If some ingress + ASBRs reset the LOCAL_PREF attribute, this AS specific g-shut + community will be used to override other LOCAL_PREF preference + changes. Note that in the case where an AS is aggregating multiple routes under a covering prefix, it is recommended to filter out the g-shut community from the resulting aggregate BGP route. By doing so, the setting of the g-shut 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 g-shut behavior. 4.2.1.2. Operations at maintenance time @@ -216,70 +211,74 @@ Note that in the case where an AS is aggregating multiple routes under a covering prefix, it is recommended to filter out the g-shut community from the resulting aggregate BGP route. By doing so, the setting of the g-shut 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 g-shut behavior. 4.2.1.2. Operations at maintenance time On the g-shut initiator, upon maintenance time, it is required to: + o apply an outbound BGP route policy on the maintained eBGP session to tag the paths propagated over the session with the g-shut community. This will trigger the BGP implementation to re- advertise all active routes previously advertised, and tag them with the g-shut community. + o apply an inbound BGP route policy on the maintained eBGP session to tag the paths received over the session with the g-shut community. o wait for convergence to happen. + o perform a BGP session shutdown. -4.2.1.3. BGP implementation support for G-Shut +4.2.1.3. BGP implementation support for g-Shut A BGP router implementation MAY provide features aimed at automating the application of the graceful shutdown procedures described above. Upon a session shutdown specified as graceful by the operator, a BGP implementation supporting a g-shut feature SHOULD: 1. On the eBGP side, update all the paths propagated over the - corresponding eBGP session, tagging the GSHUT community to them. + corresponding eBGP session, tagging the g-shut community to them. Any subsequent update sent to the session being gracefully shut - down would be tagged with the GSHUT community. + down would be tagged with the g-shut community. + 2. On the iBGP side, lower the LOCAL_PREF value of the paths received over the eBGP session being shut down, upon their - propagation over iBGP sessions. Optionally, also tag these - paths with an AS specific g-shut community. Note that - alternatively, the LOCAL_PREF of the paths received over the - eBGP session can be lowered on the g-shut initiator itself, - instead of only when propagating over its iBGP sessions. + propagation over iBGP sessions. Optionally, also tag these paths + with an AS specific g-shut community. + 3. Optionally shut down the session after a configured time. - 4. Prevent the GSHUT community from being inherited by a path that - would aggregate some paths tagged with the GSHUT community. - This behavior avoids the GSHUT procedure to be applied to the + + 4. Prevent the g-shut community from being inherited by a path that + would aggregate some paths tagged with the GSHUT community. This + behavior avoids the GSHUT procedure to be applied to the aggregate upon the graceful shutdown of one of its covered prefixes. A BGP implementation supporting a g-shut feature SHOULD also automatically install the BGP policies that are supposed to be - configured, as decribed in Section 4.2.1.1 for sessions over which + configured, as described in Section 4.2.1.1 for sessions over which g-shut is to be supported. 4.2.2. iBGP g-shut - If the iBGP topology is viable after the maintenance of the session, - i.e, if all BGP speakers of the AS have an iBGP signaling path for - all prefixes advertised on this g-shut iBGP session, then the - shutdown of an iBGP session does not lead to transient - unreachability. + For the shutdown of an iBGP session, provided the iBGP topology is + viable after the maintenance of the session, i.e, if all BGP speakers + of the AS have an iBGP signaling path for all prefixes advertised on + this g-shut iBGP session, then the shutdown of an iBGP session does + not lead to transient unreachability. As a consequence, no specific + g-shut action is required. 4.2.3. Router g-shut In the case of a shutdown of a router, a reconfiguration of the outbound BGP route policies of the g-shut initiator SHOULD be performed to set a low LOCAL_PREF value for the paths originated by the g-shut initiator (e.g, BGP aggregates redistributed from other protocols, including static routes). This behavior is equivalent to the recommended behavior for paths @@ -328,118 +327,109 @@ Corner cases leading to LoC can occur during an eBGP link up event. 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 session 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 towards the - prefix. + 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 "g-no-shut" 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. - 3. RR1 receives that path, reruns its decision process, and - picks this new path as best. As a result, RR1 withdraws its - previously announced best-path on the iBGP sessions of its RR - full-mesh. + and propagates an UPDATE within its RR full-mesh, i.e., to RR1 and + RR2. + + 3. RR1 receives that path, reruns its decision process, and picks + this new path 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 the update generated in step 2, RR3 transiently suffers from unreachability for the affected prefix. - The use of [BestExternal] among the RR of the iBGP full-mesh can - solve these corner cases by ensuring that within an AS, the - advertisement of a new route is not translated into the withdraw of a - former route. + The use of [I-D.ietf-idr-best-external] among the RR of the iBGP + full-mesh can solve these corner cases by ensuring that within an AS, + the advertisement of a new route is not translated into the 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 its non clients (e.g. other RRs in a mesh of RR) when it receives a new, preferred path over an iBGP session. 7. IANA assigned g-shut BGP community Applying the g-shut procedure is rendered much easier with the use of - a single g-shut community value which could be used on all eBGP - sessions, for both inbound and outbound signaling. The community - value 0xFFFF0000 has been assigned by IANA for this purpose. + a single g-shut BGP community value [RFC1997] which could be used on + all eBGP sessions, for both inbound and outbound signaling. The + community value 0xFFFF0000 has been assigned by IANA for this + purpose. - For Internet routes, a non transitive extended community will be - reserved from the pool defined in [EXT_POOL]. Using such a community - type allows for not leaking graceful signaling out of the AS - boundaries, without the need to explicitly configure filters to strip - the community off upon path propagation. +8. IANA Considerations -8. Security Considerations + This document has no actions for IANA. + +9. Security Considerations By providing the g-shut service to a neighboring AS, an ISP provides - means to this neighbor to lower the LOCAL_PREF value assigned to the - paths received from this neighbor. + means to this neighbor and possibly its downstream ASes to lower the + LOCAL_PREF value assigned to the paths received from this neighbor. 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 g-shut community by this neighbor. - ASes using the regular (transitive) g-shut community SHOULD remove - the community from neighboring ASes that do not support the g-shut - procedure. Doing so prevents malignant remote ASes from using the - community through intermediate ASes that do not support the feature, - in order to perform inbound traffic engineering. ASes using the non- - transitive extended community do not need to do this as the community - is non transitive and hence cannot be used by remote ASes. - -9. Acknowledgments - - The authors wish to thank Olivier Bonaventure and Pradosh Mohapatra - for their useful comments on this work. - -10. References - -10.1. Normative References +10. Acknowledgments - [REQS] Decraene, B., Francois, P., Pelsser, C., Ahmad, Z., - Armengol, A., and T. Takeda, "Requirements for the - graceful shutdown of BGP sessions", RFC 6198. + The authors wish to thank Olivier Bonaventure, Pradosh Mohapatra and + Job Snijders for their useful comments on this work. - [EXT_POOL] - Decraene, B. and P. Francois, "Assigned BGP extended - communities", - draft-ietf-idr-reserved-extended-communities-06. +11. References - [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended - Communities Attribute", RFC 4360, February 2006. +11.1. Normative References - [BGPWKC] "http://www.iana.org/assignments/ - bgp-well-known-communities". + [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, March 1997. + Requirement Levels", BCP 14, RFC 2119, + DOI 10.17487/RFC2119, March 1997, + . -10.2. Informative References + [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, + . - [AddPath] D. Walton, E. Chen, A. Retana, and J. Scudder, - "Advertisement of Multiple Paths in BGP", - draft-ietf-idr-add-paths-09.txt (work in progress). +11.2. Informative References - [BestExternal] + [I-D.ietf-idr-best-external] Marques, P., Fernando, R., Chen, E., Mohapatra, P., and H. - Gredler, "Advertisement of the best-external route to - IBGP", draft-ietf-idr-best-external-05.txt. + Gredler, "Advertisement of the best external route in + BGP", draft-ietf-idr-best-external-05 (work in progress), + January 2012. + + [RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder, + "Advertisement of Multiple Paths in BGP", RFC 7911, + DOI 10.17487/RFC7911, July 2016, + . Appendix A. Alternative techniques with limited applicability A few alternative techniques have been considered to provide g-shut 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 @@ -460,49 +450,32 @@ 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. Authors' Addresses Pierre Francois - Institute IMDEA Networks - Avda. del Mar Mediterraneo, 22 - Leganese 28918 - ES + Individual Contributor - Email: pierre.francois@imdea.org + Email: pfrpfr@gmail.com Bruno Decraene Orange - 38-40 rue du General Leclerc - 92794 Issy Moulineaux cedex 9 - FR Email: bruno.decraene@orange.com - Cristel Pelsser - Internet Initiative Japan - Jinbocho Mitsui Bldg. - 1-105 Kanda Jinbo-cho - Tokyo 101-0051 - JP + Strasbourg University - Email: cristel@iij.ad.jp + Email: pelsser@unistra.fr Keyur Patel - Cisco Systems - 170 West Tasman Dr - San Jose, CA 95134 - US + Arrcus, Inc. - Email: keyupate@cisco.com + Email: keyur@arrcus.com Clarence Filsfils Cisco Systems - De kleetlaan 6a - Diegem 1831 - BE Email: cfilsfil@cisco.com