--- 1/draft-ietf-grow-bgp-graceful-shutdown-requirements-04.txt 2010-10-11 23:14:09.000000000 +0200 +++ 2/draft-ietf-grow-bgp-graceful-shutdown-requirements-05.txt 2010-10-11 23:14:10.000000000 +0200 @@ -4,24 +4,24 @@ Intended status: Informational P. Francois UCL C. Pelsser IIJ Z. Ahmad Orange Business Services A. J. Elizondo Armengol Telefonica I+D T. Takeda NTT - September 06, 2010 + October 11, 2010 Requirements for the graceful shutdown of BGP sessions - draft-ietf-grow-bgp-graceful-shutdown-requirements-04.txt + draft-ietf-grow-bgp-graceful-shutdown-requirements-05.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. 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 @@ -40,21 +40,21 @@ 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. - This Internet-Draft will expire on March 05, 2011. + This Internet-Draft will expire on April 09, 2011. Requirements for the graceful shutdown of BGP sessions Copyright Notice Copyright (c) 2010 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 @@ -82,47 +82,47 @@ requirements for such a solution. Table of Contents 1. Conventions used in this document...........................3 2. Introduction................................................3 3. Problem statement...........................................4 3.1. Example of undesirable BGP routing behavior.................4 3.2. Causes of packet loss.......................................5 4. Terminology.................................................6 - 5. Goals and requirements......................................6 - 6. Reference Topologies........................................8 + 5. Goals and requirements......................................7 + 6. Reference Topologies........................................9 6.1. E-BGP topologies............................................9 6.2. I-BGP topologies...........................................11 7. Security Considerations....................................14 - 8. IANA Considerations........................................14 - 9. References.................................................14 - 9.1. Normative References.......................................14 - 9.2. Informative References.....................................14 + 8. IANA Considerations........................................15 + 9. References.................................................15 + 9.1. Normative References.......................................15 + 9.2. Informative References.....................................15 10. Acknowledgments............................................15 - 11. Author's Addresses.........................................15 + 11. Author's Addresses.........................................16 Requirements for the graceful shutdown of BGP sessions 1. Conventions used in this document 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. Introduction - The Border Gateway Protocol(BGP) is heavily used in Service Provider - networks both for Internet and BGP/MPLS VPN services. For resiliency - purposes, redundant routers and BGP sessions can be deployed to - reduce the consequences of an AS Border Router or BGP session - breakdown on customers' or peers' traffic. + The Border Gateway Protocol(BGP) [BGP-4] is heavily used in Service + Provider networks both for Internet and BGP/MPLS VPN services [VPN]. + For resiliency purposes, redundant routers and BGP sessions can be + deployed to reduce the consequences of an AS Border Router or BGP + session breakdown on customers' or peers' traffic. We place ourselves in the context where a Service Provider performs a maintenance operation and needs to shut down one or multiple BGP peering link(s) or a whole ASBR. If an alternate path is available within the AS, the requirement is to avoid or reduce customer or peer traffic loss during the BGP convergence. Indeed, as an alternate path is available in the Autonomous System (AS), it should be made possible to reroute the customer or peer traffic on this backup path before the BGP session(s) is/are torn down, the nominal path withdrawn and the forwarding is interrupted on the nominal path. @@ -234,26 +234,25 @@ When multiple BGP routers are involved and plenty of prefixes are affected, the recovery process can take longer than applications requirements. 3.2. Causes of packet loss The loss of packets during the maintenance has two main causes: - lack of an alternate path on some routers, - transient routing inconsistency. +Requirements for the graceful shutdown of BGP sessions + Some routers may lack an alternate path because another router is hiding the backup path. This router can be: - a route reflector only propagating its best path; - -Requirements for the graceful shutdown of BGP sessions - - the backup ASBR not advertising the backup path because it prefers the nominal path. This lack of knowledge of the alternate path is the first target of this requirement draft. Transient routing inconsistencies happen during IBGP convergence because all routers are not updating their RIB at the same time. This can lead to forwarding loops and then packet drops. The duration of these transient micro-loops may depend on the IBGP topology (e.g. number of Route Reflectors between ingress and egress ASBR), @@ -261,106 +260,117 @@ update the RIB and FIB, possibly the order in which prefixes are modified), forwarding mode (hop by hop IP forwarding versus tunneling). Transient forwarding loops can be avoided by performing only one IP lookup on BGP routes in each AS and by using tunnels (e.g. MPLS LSP) to send packets between ASBRs. As such, BGP/MPLS VPNs should be immune to such micro forwarding loops. 4. Terminology + g-shut: Graceful SHUTdown. A method for explicitly notifying the BGP + routers that a BGP session (and hence the prefixes learnt over that + session) is going to be disabled. + + g-noshut: Graceful NO SHUTdown. A method for explicitly notifying + the BGP routers that a BGP session (and hence the prefixes learnt + over that session) is going to be enabled. + g-shut initiator: the router on which the session(s) shutdown is (are) performed for the maintenance. g-shut neighbor: a router that peers with the g-shut initiator via (one of) the session(s) undergoing maintenance. Affected prefixes: a prefix initially reached via the peering link(s) undergoing maintenance. Affected router: a router reaching an affected prefix via a peering link undergoing maintenance. Initiator AS: the autonomous system of the g-shut initiator router. Neighbor AS(es): the autonomous system(s) of the g-shut neighbor router(s). +Requirements for the graceful shutdown of BGP sessions + 5. Goals and requirements When a BGP session of the router under maintenance is shut down, the router removes the routes and then triggers the BGP convergence on its BGP peers. The goal of BGP graceful shutdown is to initiate the BGP convergence to find the alternate paths before the nominal paths are removed. As a result, before the nominal BGP session is shut down, all routers learn and use the alternate paths. Then the nominal BGP session can be shut down. - As a result, provided an alternate path is available in the AS, the - packets are rerouted before the BGP session termination and fewer - -Requirements for the graceful shutdown of BGP sessions - - packets (possibly none) are lost during the BGP convergence process - since at any time, all routers have a valid path. + As a result, provided an alternate path with enough remaining + capacity is available in the AS, the packets are rerouted before the + BGP session termination and fewer packets (possibly none) are lost + during the BGP convergence process since at any time, all routers + have a valid path. Another goal is to minimize packet loss when the BGP session is re- established following the maintenance. From the above goals we can derive the following requirements: a) A mechanism to advertise the maintenance action to all affected routers is REQUIRED. Such mechanism may be either implicit or explicit. Note that affected routers can be located both in the local AS and in neighboring ASes. Note also that the maintenance action can either be the shutdown of a BGP session or the establishment of a BGP session. - The mechanism SHOULD minimize packet loss when a path is removed or - advertised. In particular, it SHOULD be ensured that the old path is - not removed from the routing tables of the affected routers before - the new path is known. + The mechanism SHOULD allow BGP routers to minimize packet loss when a + path is removed or advertised. In particular, it SHOULD be ensured + that the old path is not removed from the routing tables of the + affected routers before the new path is known. + The solution mechanism MUST reduce packet loss but MAY provide only a + reduction rather than full minimization, in order to trade off with + simplicity of implementation and operation as shown in some of the + following requirements. b) An Internet wide convergence is OPTIONAL. However if the initiator AS and the neighbor AS(es) have a backup path, they SHOULD be able to gracefully converge before the nominal path is shut down. c) The proposed solution SHOULD be applicable to any kind of BGP sessions (EBGP, IBGP, IBGP route reflector client, EBGP confederations, EBGP multi hop, MultiProtocol BGP extension...) and any address family. If a BGP implementation allows closing a sub-set of AFIs carried in a MP-BGP session, this mechanism MAY be applicable to this sub-set of AFIs. Depending on the session type (EBGP, IBGP...), there may be some variations in the proposed solution in order to fulfill the requirements. +Requirements for the graceful shutdown of BGP sessions + The following cases should be handled in priority: - The shutdown of an inter-AS link and therefore the shutdown of an eBGP session; - The shutdown of an AS Border Router and therefore the shutdown of all its BGP sessions. Service Providers and platforms implementing a graceful shutdown solution should note that in BGP/MPLS VPN as per [VPN], the PE-CE routing can be performed by other protocols than BGP (e.g. static routes, RIPv2, OSPF, IS-IS...). This is out of scope of this - document, but comprehensive graceful shutdown procedures should take - this into account. + document. d) The proposed solution SHOULD NOT change the BGP convergence behavior for the ASes exterior to the maintenance process, namely ASes other than the initiator AS and it(s) neighbor AS(es). -Requirements for the graceful shutdown of BGP sessions - e) An incremental deployment on a per AS or per BGP session basis SHOULD be made possible. In case of partial deployment the proposed solution SHOULD incrementally improve the maintenance process. The solution SHOULD bring improvements even when one of the two ASes does not support graceful shutdown. In particular, large Service Providers may not be able to upgrade all of the deployed customer premises access routers (CPE). f) Redistribution or advertisement of (static) IP routes into BGP SHOULD also be covered. @@ -373,47 +383,48 @@ following the g-shut and once the BGP session is gracefully opened following the g-noshut. In the end, once the planned maintenance is finished the nominal BGP routing MUST be reestablished. The duration of the g-shut procedure, and hence the time before the BGP session is safely closed SHOULD be discussed by the solution document. Examples of possible solutions are the use of a pre- configured timer, of a message to signal the end of the BGP convergence or monitoring the traffic on the g-shut interface... i) The solution SHOULD be simple and simple to operate. Hence it - MAY only cover a subset of the cases. + MAY only cover a subset of the cases. (As a consequence, most of the + above requirements are expressed as "SHOULD" rather than "MUST") The metrics to evaluate and compare the proposed solutions are, in decreasing order of importance: - The duration of the remaining loss of connectivity when the BGP session is brought down or up + +Requirements for the graceful shutdown of BGP sessions + - The applicability to a wide range of BGP and network topologies, especially those described in section 6; - The simplicity; - The duration of transient forwarding loops; - The additional load introduced in BGP (eg BGP messages sent to peer routers, peer ASes, the Internet). 6. Reference Topologies In order to benchmark the proposed solutions, some typical BGP - topologies are detailed in this section. The solution drafts - should state its applicability for each of these possible - topologies. + topologies are detailed in this section. The solution documents + should state the applicability of the solutions for each of these + possible topologies. However, solutions SHOULD be applicable to all possible BGP topologies and not only to these below examples. Note that this is a "SHOULD" rather than a "MUST" as a partial lightweight solution may be preferred to a full but more complex solution. - -Requirements for the graceful shutdown of BGP sessions - Especially since some ISP may not be concerned by some topologies (e.g. confederations). 6.1. EBGP topologies We describe here some frequent EBGP topologies that SHOULD be supported by the solution. 6.1.1. 1 ASBR in AS1 connected to two ASBRs in the neighboring AS2 @@ -433,35 +444,36 @@ \ ' \----------- ASBR2.2 ' ' AS1 ' AS2 ' Figure 2. EBGP topology with redundant ASBR in one of the AS. The requirements of section 5 should be applicable to: + +Requirements for the graceful shutdown of BGP sessions + - Maintenance of one of the routers of AS2; - Maintenance of one link between AS1 and AS2, performed either on an AS1 or AS2 router. Note that in case of maintenance of the whole router, all its BGP session needs to be shutdown. 6.1.2. 2 ASBRs in AS1 connected to 2 ASBRs in AS2 In this topology we have a symmetric protection scheme between AS1 and AS2: on both sides, two different routers are used to connect AS1 to AS2. -Requirements for the graceful shutdown of BGP sessions - ' AS1 ' AS2 ' ASBR1.1----------- ASBR2.1 ' ' ' ' ' ASBR1.2----------- ASBR2.2 @@ -475,20 +487,22 @@ - Maintenance of any of the ASBR routers (in AS1 or AS2); - Maintenance of one link between AS1 and AS2 performed either on an AS1 or AS2 router. 6.1.3. 2 ASBRs in AS2 each connected to two different ASes In this topology at least three ASes are involved. Depending on which routes are exchanged between these ASes, some protection for some of the traffic may be possible. +Requirements for the graceful shutdown of BGP sessions + ' AS1 ' AS2 ' ASBR1.1----------- ASBR2.1 | ' | ' '''''|'''''''''' | ' | ' ASBR3.1----------- ASBR2.2 @@ -499,22 +513,20 @@ The requirements of section 5 do not translate as easily as in the two previous topologies because we do not require propagating the maintenance advertisement outside of the two ASes involved in an eBGP session. For instance if ASBR2.2 requires a maintenance affecting ASBR3.1, then ASBR3.1 will be notified. However we do not require for ASBR1.1 to be notified of the maintenance of the eBGP session between ASBR3.1-ASBR2.2. -Requirements for the graceful shutdown of BGP sessions - 6.2. IBGP topologies We describe here some frequent IBGP topologies that SHOULD be supported by the solution. 6.2.1. IBGP Full-Mesh In this topology we have a full mesh of iBGP sessions: P1 ------ P2 @@ -527,30 +539,31 @@ \ / \ / ''''''\''''/'''''''''''' \ / AS2 ASBR2.1 Figure 5. IBGP full mesh When the session between ASBR1.1 and ASBR2.1 undergoes maintenance, it is required that all IBGP peers of ASBR1.1 reroute + +Requirements for the graceful shutdown of BGP sessions + traffic to ASBR1.2 before the session between ASBR1.1 and ASBR2.1 is shut down. 6.2.2. Route Reflector In this topology, route reflectors are used to limit the number of IBGP sessions. -Requirements for the graceful shutdown of BGP sessions - P1 RR----- P2 RR | \ / | | \ / | | \ / | AS1 | \ / | | / \ | | / \ | | / \ | ASBR1.1 ASBR1.2 \ / @@ -565,20 +578,22 @@ When the session between ASBR1.1 and ASBR2.1 undergoes maintenance, it is required that all BGP routers of AS1 reroute traffic to ASBR1.2 before the session between ASBR1.1 and ASBR2.1 is shut down. 6.2.3. hierarchical Route Reflector In this topology, hierarchical route reflectors are used to limit the number of IBGP sessions. +Requirements for the graceful shutdown of BGP sessions + P1/hRR -------- P2/hRR | | | | | | AS1 | | | | P3/RR P4/RR | | | | @@ -588,40 +603,40 @@ ASBR1.1 ASBR1.2 \ / \ / ''''''\'''''''''/'''''''''''' \ / \ / AS2 ASBR2.1 Figure 7. Hierarchical Route Reflector -Requirements for the graceful shutdown of BGP sessions - When the session between ASBR1.1 and ASBR2.1 undergoes maintenance, it is required that all BGP routers of AS1 reroute traffic to ASBR1.2 before the session between ASBR1.1 and ASBR2.1 is shut down. 6.2.4. Confederations In this topology, a confederation of ASs is used to limit the number of IBGP sessions. Moreover, RRs may be present in the member ASs of the confederation. Confederations may be run with different sub-options. Regarding the IGP, each member AS can run its own IGP or they can all share the same IGP. Regarding BGP, local_pref may or may not cross the member AS boundaries. A solution should support the shutdown of EBGP sessions between member-ASs in the confederation in addition to the shutdown of EBGP sessions between a member-AS and an AS outside of the confederation. +Requirements for the graceful shutdown of BGP sessions + ASBR1C.1 ---------- ASBR1C.2 | | | | | AS1C | | | | | """|"""""""""""""""""""|""" | " | ASBR1A.2 " ASBR1B.2 | " | @@ -640,31 +655,43 @@ Figure 8. Confederation In the above figure, member-AS AS1A, AS1B, AS1C belong to a confederation of ASs in AS1. AS1A and AS1B are connected to AS2. In normal operation, for the traffic toward AS2, . AS1A sends the traffic directly to AS2 through ASBR1A.1 . AS1B sends the traffic directly to AS2 through ASBR1B.1 . AS1C load balances the traffic between AS1A and AS1B -Requirements for the graceful shutdown of BGP sessions - When the session between ASBR1A.1 and ASBR2.1 undergoes maintenance, it is required that all BGP routers of AS1 reroute traffic to ASBR1B.1 before the session between ASBR1A.1 and ASBR2.1 is shut down. 7. Security Considerations + At the requirements stage, this graceful shutdown mechanism is + expected to not affect the security of the BGP protocol, especially + if it can be kept simple. No new sessions are required and the + additional ability to signal the graceful shutdown is not expected to + bring additional attack vector as BGP neighbors already have the + ability to send incorrect or misleading information or even shut down + the session. + Security considerations MUST be addressed by the proposed - solutions. + solutions. In particular they SHOULD address the issues of bogus + g-shut messages and how they would affect the network(s), as well + +Requirements for the graceful shutdown of BGP sessions + + as the impact of hiding a g-shut message so that g-shut is not + performed. The solution SHOULD NOT increase the ability for one AS to selectively influence routing decision in the peer AS (inbound Traffic Engineering) outside the case of the BGP session shutdown. Otherwise, the peer AS SHOULD have means to detect such behavior. 8. IANA Considerations This document has no actions for IANA. @@ -693,30 +720,30 @@ 9.2. Informative References [RFC5817] Z. Ali, J.P. Vasseur, A. Zamfir and J. Newton "Graceful Shutdown in MPLS and Generalized MPLS Traffic Engineering Networks", RFC 5817 April 2010. [GR] S. Sangli, E. Chen, R. Fernando, J. Scudder, Y. Rekhter "Graceful Restart Mechanism for BGP", RFC 4724 January 2007. [Reliability] Network Strategy Partners, LLC. - -Requirements for the graceful shutdown of BGP sessions - "Reliable IP Nodes: A prerequisite to profitable IP services", November 2002. http://www.nspllc.com/NewPages/Reliable_IP_Nodes.pdf 10. Acknowledgments Authors would like to thank Nicolas Dubois, Benoit Fondeviole, Christian Jacquenet, Olivier Bonaventure, Steve Uhlig, Xavier + +Requirements for the graceful shutdown of BGP sessions + Vinet, Vincent Gillet, Jean-Louis le Roux, Pierre Alain Coste and Ronald Bonica for the useful discussions on this subject, their review and comments. This draft has been partly sponsored by the European project IST AGAVE. Authors' Addresses Bruno Decraene @@ -744,28 +771,28 @@ Email: cristel@iij.ad.jp Zubair Ahmad Orange Business Services 13775 McLearen Road, Oak Hill VA 20171 USA Email: zubair.ahmad@orange-ftgroup.com -Requirements for the graceful shutdown of BGP sessions - Antonio Jose Elizondo Armengol Division de Analisis Tecnologicos Technology Analysis Division Telefonica I+D C/ Emilio Vargas 6 28043, Madrid +Requirements for the graceful shutdown of BGP sessions + E-mail: ajea@tid.es Tomonori Takeda NTT Corporation 9-11, Midori-Cho 3 Chrome Musashino-Shi, Tokyo 180-8585 Japan Email: takeda.tomonori@lab.ntt.co.jp