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rfc:rfc5817

Internet Engineering Task Force (IETF) Z. Ali Request for Comments: 5817 JP. Vasseur Category: Informational A. Zamfir ISSN: 2070-1721 Cisco Systems, Inc.

                                                             J. Newton
                                                    Cable and Wireless
                                                            April 2010
           Graceful Shutdown in MPLS and Generalized MPLS
                    Traffic Engineering Networks

Abstract

 MPLS-TE Graceful Shutdown is a method for explicitly notifying the
 nodes in a Traffic Engineering (TE) enabled network that the TE
 capability on a link or on an entire Label Switching Router (LSR) is
 going to be disabled.  MPLS-TE graceful shutdown mechanisms are
 tailored toward addressing planned outage in the network.
 This document provides requirements and protocol mechanisms to reduce
 or eliminate traffic disruption in the event of a planned shutdown of
 a network resource.  These operations are equally applicable to both
 MPLS-TE and its Generalized MPLS (GMPLS) extensions.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc5817.

Ali, et al. Informational [Page 1] RFC 5817 MPLS Graceful Shutdown April 2010

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
 (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 ....................................................3
 2. Terminology .....................................................3
 3. Requirements for Graceful Shutdown ..............................4
 4. Mechanisms for Graceful Shutdown ................................5
    4.1. OSPF / IS-IS Mechanisms for Graceful Shutdown ..............5
    4.2. RSVP-TE Signaling Mechanisms for Graceful Shutdown .........6
 5. Manageability Considerations ....................................8
 6. Security Considerations .........................................8
 7. Acknowledgments .................................................8
 8. References ......................................................9
    8.1. Normative References .......................................9
    8.2. Informative References .....................................9

Ali, et al. Informational [Page 2] RFC 5817 MPLS Graceful Shutdown April 2010

1. Introduction

 When outages in a network are planned (e.g., for maintenance
 purposes), some mechanisms can be used to avoid traffic disruption.
 This is in contrast with unplanned network element failure, where
 traffic disruption can be minimized thanks to recovery mechanisms,
 but may not be avoided.  Therefore, a Service Provider may desire to
 gracefully (temporarily or indefinitely) remove a TE link, a group of
 TE links, or an entire node for administrative reasons such as link
 maintenance, software/hardware upgrade at a node, or significant TE
 configuration changes.  In all these cases, the goal is to minimize
 the impact on the traffic carried over TE LSPs in the network by
 triggering notifications so as to gracefully reroute such flows
 before the administrative procedures are started.
 These operations are equally applicable to both MPLS-TE [RFC3209] and
 its Generalized MPLS (GMPLS) extensions [RFC3471] [RFC3473].
 This document describes the mechanisms that can be used to gracefully
 shut down MPLS-TE / GMPLS-TE on a resource such as a TE link, a
 component link within a bundled TE link, a label resource, or an
 entire TE node.
 Graceful shutdown of a resource may require several steps.  These
 steps can be broadly divided into two sets: disabling the resource in
 the control plane and disabling the resource in the data plane.  The
 node initiating the graceful shutdown condition introduces a delay
 between the two sets to allow the control plane to gracefully divert
 the traffic away from the resource being gracefully shut down.  The
 trigger for the graceful shutdown event is a local matter at the node
 initiating the graceful shutdown.  Typically, graceful shutdown is
 triggered for administrative reasons, such as link maintenance or
 software/hardware upgrade.

2. Terminology

 LSR: Label Switching Router.  The terms node and LSR are used
    interchangeably in this document.
 GMPLS: The term GMPLS is used in this document to refer to packet
    MPLS-TE, as well as GMPLS extensions to MPLS-TE.
 TE Link: The term TE link refers to a single link or a bundle of
    physical links or FA-LSPs (see below) on which traffic engineering
    is enabled.
 TE LSP: A Traffic Engineered Label Switched Path.

Ali, et al. Informational [Page 3] RFC 5817 MPLS Graceful Shutdown April 2010

 S-LSP: A segment of a TE LSP.
 FA-LSP (Forwarding Adjacency LSP): An LSP that is announced as a TE
    link into the same instance of the GMPLS control plane as the one
    that was used to create the LSP [RFC4206].
 ISIS-LSP: Link State Packet that is generated by IS-IS routers and
    that contains routing information.
 LSA: Link State Advertisement that is generated by OSPF routers and
    that contains routing information.
 TE LSA / TE-IS-IS-LSP: The traffic engineering extensions to OSPF /
    IS-IS.
 Head-end node: Ingress LSR that initiated signaling for the Path.
 Border node: Ingress LSR of a TE LSP segment (S-LSP).
 PCE (Path Computation Element): An entity that computes the routes on
    behalf of its clients (PCC) [RFC4655].
 Last-resort resource: If a path to a destination from a given head-
    end node cannot be found upon removal of a resource (e.g., TE
    link, TE node), the resource is called "last resort" to reach that
    destination from the given head-end node.

3. Requirements for Graceful Shutdown

 This section lists the requirements for graceful shutdown in the
 context of GMPLS.
  1. Graceful shutdown is required to address graceful removal of one TE

link, one component link within a bundled TE link, a set of TE

   links, a set of component links, label resources, or an entire
   node.
  1. Once an operator has initiated graceful shutdown of a network

resource, no new TE LSPs may be set up that use the resource. Any

   signaling message for a new TE LSP that explicitly specifies the
   resource, or that would require the use of the resource due to
   local constraints, is required to be rejected as if the resource
   were unavailable.
  1. It is desirable for new TE LSP set-up attempts that would be

rejected because of graceful shutdown of a resource (as described

   in the previous requirement) to avoid any attempt to use the
   resource by selecting an alternate route or other resources.

Ali, et al. Informational [Page 4] RFC 5817 MPLS Graceful Shutdown April 2010

  1. If the resource being shut down is a last-resort resource, based on

a local decision, the node initiating the graceful shutdown

   procedure can cancel the shutdown operation.
  1. It is required to give the ingress node the opportunity to take

actions in order to reduce or eliminate traffic disruption on the

   TE LSPs that are using the network resources that are about to be
   shut down.
  1. Graceful shutdown mechanisms are equally applicable to intra-domain

TE LSPs and those spanning multiple domains, as defined in

   [RFC4726].  Examples of such domains include IGP areas and
   Autonomous Systems.
  1. Graceful shutdown is equally applicable to packet and non-packet

networks.

  1. In order to make rerouting effective, it is required that when a

node initiates the graceful shutdown of a resource, it notifies all

   other network nodes about the TE resource under graceful shutdown.
  1. Depending on switching technology, it may be possible to shut down

a label resource, e.g., shutting down a lambda in a Lambda Switch

   Capable (LSC) node.

4. Mechanisms for Graceful Shutdown

 An IGP-only solution based on [RFC3630], [RFC5305], [RFC4203] and
 [RFC5307] is not applicable when dealing with inter-area and inter-AS
 traffic engineering, as IGP flooding is restricted to IGP
 areas/levels.  An RSVP-based solution is proposed in this document to
 handle TE LSPs spanning multiple domains.  In addition, in order to
 discourage nodes from establishing new TE LSPs through the resources
 being shut down, existing IGP mechanisms are used for the shutdown
 notification.
 A node where a link or the whole node is being shut down first
 triggers the IGP updates as described in Section 4.1 and then, with
 some delay to allow network convergence, uses the signaling mechanism
 described in Section 4.2.

4.1. OSPF / IS-IS Mechanisms for Graceful Shutdown

 This section describes the use of existing OSPF and IS-IS mechanisms
 for the graceful shutdown in GMPLS networks.

Ali, et al. Informational [Page 5] RFC 5817 MPLS Graceful Shutdown April 2010

 The OSPF and IS-IS procedures for graceful shutdown of TE links are
 similar to the graceful restart of OSPF and IS-IS as described in
 [RFC4203] and [RFC5307], respectively.  Specifically, the node where
 graceful shutdown of a link is desired originates the TE LSA or IS-
 IS-LSP containing a Link TLV for the link under graceful shutdown
 with the Traffic Engineering metric set to 0xffffffff, 0 as
 unreserved bandwidth.  If the TE link has LSC or FSC as its Switching
 Capability, then it also has 0 in the "Max LSP Bandwidth" field of
 the Interface Switching Capability Descriptor (ISCD) sub-TLV.  A node
 may also specify a value that is greater than the available bandwidth
 in the "Minimum LSP bandwidth" field of the same ISCD sub-TLV.  This
 would discourage new TE LSP establishment through the link under
 graceful shutdown.
 If the graceful shutdown procedure is performed for a component link
 within a TE link bundle and it is not the last component link
 available within the TE link, the link attributes associated with the
 TE link are recomputed.  Similarly, if the graceful shutdown
 procedure is performed on a label resource within a TE link, the link
 attributes associated with the TE link are recomputed.  If the
 removal of the component link or label resource results in a
 significant bandwidth change event, a new LSA is originated with the
 new traffic parameters.  If the last component link is being shut
 down, the routing procedure related to TE link removal is used.
 Neighbors of the node where graceful shutdown procedure is in
 progress continue to advertise the actual unreserved bandwidth of the
 TE links from the neighbors to that node, without any routing
 adjacency change.
 When graceful shutdown at node level is desired, the node in question
 follows the procedure specified in the previous section for all TE
 links.

4.2 RSVP-TE Signaling Mechanisms for Graceful Shutdown

 As discussed in Section 3, one of the requirements for the signaling
 mechanism for graceful shutdown is to carry information about the
 resource under graceful shutdown.  For this purpose, the graceful
 shutdown procedure uses TE LSP rerouting mechanism as defined in
 [RFC5710].
 Specifically, the node where graceful shutdown of an unbundled TE
 link or an entire bundled TE link is desired triggers a PathErr
 message with the error code "Notify" and error value "Local link
 maintenance required", for all affected TE LSPs.  Similarly, the node
 that is being gracefully shut down triggers a PathErr message with
 the error code "Notify" and error value "Local node maintenance

Ali, et al. Informational [Page 6] RFC 5817 MPLS Graceful Shutdown April 2010

 required", for all TE LSPs.  For graceful shutdown of a node, an
 unbundled TE link, or an entire bundled TE link, the PathErr message
 may contain either an [RFC2205] format ERROR_SPEC object or an IF_ID
 [RFC3473] format ERROR_SPEC object.  In either case, it is the
 address and TLVs carried by the ERROR_SPEC object and not the error
 value that indicate the resource that is to be gracefully shut down.
 MPLS-TE link bundling [RFC4201] requires that an TE LSP is pinned
 down to a component link.  Consequently, graceful shutdown of a
 component link in a bundled TE link differs from graceful shutdown of
 unbundled TE link or entire bundled TE link.  Specifically, in the
 former case, when only a subset of component links and not the entire
 bundled TE link is being shut down, the remaining component links of
 the bundled TE link may still be able to admit new TE LSPs.  The node
 where graceful shutdown of a component link is desired triggers a
 PathErr message with the error code "Notify" and error value of
 "Local link maintenance required".  The rest of the ERROR_SPEC object
 is constructed using Component Reroute Request procedure defined in
 [RFC5710].
 If graceful shutdown of a label resource is desired, the node
 initiating this action triggers a PathErr message with the error
 codes and error values of "Notify/Local link maintenance required".
 The rest of the ERROR_SPEC object is constructed using the Label
 Reroute Request procedure defined in [RFC5710].
 When a head-end node, a transit node, or a border node receives a
 PathErr message with the error code "Notify" and error value "Local
 link maintenance required" or "Local node maintenance required", it
 follows the procedures defined in [RFC5710] to reroute the traffic
 around the resource being gracefully shut down.  When performing path
 computation for the new TE LSP, the head-end node or border node
 avoids using the TE resources identified by the ERROR_SPEC object.
 If the PCE is used for path computation, the head-end (or border)
 node acting as PCC specifies in its requests to the PCE that path
 computation should avoid the resource being gracefully shut down.
 The amount of time the head-end node or border node avoids using the
 TE resources identified by the IP address contained in the PathErr is
 based on a local decision at that node.
 If the node initiating the graceful shutdown procedure receives a
 path setup request for a new tunnel-using resource being gracefully
 shut down, it sends a PathErr message with "Notify" error code in the
 ERROR SPEC object and an error value consistent with the type of
 resource being gracefully shut down.  However, based on a local
 decision, if an existing tunnel continues to use the resource being
 gracefully shut down, the node initiating the graceful shutdown
 procedure may allow that resource being gracefully shut down to be

Ali, et al. Informational [Page 7] RFC 5817 MPLS Graceful Shutdown April 2010

 used as a "last resort".  The node initiating the graceful shutdown
 procedure can distinguish between new and existing tunnels by
 inspecting the SENDER TEMPLATE and SESSION objects.
 If the resource being shut down is a last-resort resource, it can be
 used; i.e., based on a local decision, the node initiating the
 graceful shutdown procedure can cancel the shutdown operation.
 Similarly, based on a local decision, the node initiating the
 graceful shutdown procedure can delay the actual removal of resource
 for forwarding.  This is to give time to the network to move traffic
 from the resource being shut down.  For this purpose, the node
 initiating graceful shutdown procedure follows the Reroute Request
 Timeout procedure defined in [RFC5710].

5. Manageability Considerations

 When a TE link is being shut down, a linkDown trap as defined in
 [RFC2863] should be generated for the TE link.  Similarly, if a
 bundled TE link is being shut down, a linkDown trap as defined in
 [RFC2863] should be generated for the bundled TE link, as well as for
 each of its component links.  If a TE node is being shut down, a
 linkDown trap as defined in [RFC2863] should be generated for all TE
 links at the node.

6. Security Considerations

 This document introduces no new security considerations as it
 describes usage of existing formats and mechanisms.  This document
 relies on existing procedures for advertisement of TE LSA / IS-IS-
 LSPs containing Link TLVs.  Tampering with TE LSAs / IS-IS-LSPs may
 have an effect on traffic engineering computations, and it is
 suggested that any mechanisms used for securing the transmission of
 normal LSAs / IS-IS-LSPs be applied equally to all Opaque LSAs / IS-
 IS-LSPs that this document uses.  Existing security considerations
 specified in [RFC3630], [RFC5305], [RFC4203], [RFC5307], and
 [MPLS-GMPLS-SEC] remain relevant and suffice.  Furthermore, the
 Security Considerations section in [RFC5710] and section 9 of
 [RFC4736] should be used for understanding the security
 considerations related to the formats and mechanisms used in this
 document.

7. Acknowledgments

 The authors would like to thank Adrian Farrel for his detailed
 comments and suggestions.  The authors would also like to acknowledge
 useful comments from David Ward, Sami Boutros, and Dimitri
 Papadimitriou.

Ali, et al. Informational [Page 8] RFC 5817 MPLS Graceful Shutdown April 2010

8. References

8.1. Normative References

 [RFC2205]        Braden, R., Ed., Zhang, L., Berson, S., Herzog, S.,
                  and S. Jamin, "Resource ReSerVation Protocol (RSVP)
                  -- Version 1 Functional Specification", RFC 2205,
                  September 1997.
 [RFC5710]        Berger, L., Papadimitriou, D., and JP. Vasseur,
                  "PathErr Message Triggered MPLS and GMPLS LSP
                  Reroutes", RFC 5710, January 2010.

8.2. Informative References

 [RFC3209]        Awduche, D., Berger, L., Gan, D., Li, T.,
                  Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions
                  to RSVP for LSP Tunnels", RFC 3209, December 2001.
 [RFC4736]        Vasseur, JP., Ed., Ikejiri, Y., and R. Zhang,
                  "Reoptimization of Multiprotocol Label Switching
                  (MPLS) Traffic Engineering (TE) Loosely Routed Label
                  Switched Path (LSP)", RFC 4736, November 2006.
 [RFC3630]        Katz, D., Kompella, K., and D. Yeung, "Traffic
                  Engineering (TE) Extensions to OSPF Version 2", RFC
                  3630, September 2003.
 [RFC5305]        Li, T. and H. Smit, "IS-IS Extensions for Traffic
                  Engineering", RFC 5305, October 2008.
 [RFC4203]        Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF
                  Extensions in Support of Generalized Multi-Protocol
                  Label Switching (GMPLS)", RFC 4203, October 2005.
 [RFC5307]        Kompella, K., Ed., and Y. Rekhter, Ed., "IS-IS
                  Extensions in Support of Generalized Multi-Protocol
                  Label Switching (GMPLS)", RFC 5307, October 2008.
 [RFC3471]        Berger, L., Ed., "Generalized Multi-Protocol Label
                  Switching (GMPLS) Signaling Functional Description",
                  RFC 3471, January 2003.
 [RFC3473]        Berger, L., Ed., "Generalized Multi-Protocol Label
                  Switching (GMPLS) Signaling Resource ReserVation
                  Protocol-Traffic Engineering (RSVP-TE) Extensions",
                  RFC 3473, January 2003.

Ali, et al. Informational [Page 9] RFC 5817 MPLS Graceful Shutdown April 2010

 [RFC4726]        Farrel, A., Vasseur, J.-P., and A. Ayyangar, "A
                  Framework for Inter-Domain Multiprotocol Label
                  Switching Traffic Engineering", RFC 4726, November
                  2006.
 [RFC4201]        Kompella, K., Rekhter, Y., and L. Berger, "Link
                  Bundling in MPLS Traffic Engineering (TE)", RFC
                  4201, October 2005.
 [RFC4206]        Kompella, K. and Y. Rekhter, "Label Switched Paths
                  (LSP) Hierarchy with Generalized Multi-Protocol
                  Label Switching (GMPLS) Traffic Engineering (TE)",
                  RFC 4206, October 2005.
 [RFC4655]        Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
                  Computation Element (PCE)-Based Architecture", RFC
                  4655, August 2006.
 [RFC2863]        McCloghrie, K. and F. Kastenholz, "The Interfaces
                  Group MIB", RFC 2863, June 2000.
 [MPLS-GMPLS-SEC] Luyuan F., Ed., "Security Framework for PLS and
                  GMPLS Networks", Work in Progress, March 2010.

Ali, et al. Informational [Page 10] RFC 5817 MPLS Graceful Shutdown April 2010

Authors' Addresses

 Zafar Ali
 Cisco systems, Inc.,
 2000 Innovation Drive
 Kanata, Ontario, K2K 3E8
 Canada
 EMail: zali@cisco.com
 Jean Philippe Vasseur
 Cisco Systems, Inc.
 300 Beaver Brook Road
 Boxborough, MA  01719
 USA
 EMail: jpv@cisco.com
 Anca Zamfir
 Cisco Systems, Inc.
 2000 Innovation Drive
 Kanata, Ontario, K2K 3E8
 Canada
 EMail: ancaz@cisco.com
 Jonathan Newton
 Cable and Wireless
 EMail: jonathan.newton@cw.com

Ali, et al. Informational [Page 11]

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