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Versions: (draft-ali-ccamp-mpls-graceful-shutdown) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 RFC 5817

CCAMP Working Group
Internet Draft
                                                           Zafar Ali
                                               Jean-Philippe Vasseur
                                                         Anca Zamfir
                                                 Cisco Systems, Inc.
                                                     Jonathan Newton
                                                  Cable and Wireless

Category: Informational
Expires: July 19, 2010                              January 20, 2010


           draft-ietf-ccamp-mpls-graceful-shutdown-13.txt

           Graceful Shutdown in MPLS and Generalized MPLS
                    Traffic Engineering Networks


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance
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   This Internet-Draft will expire on July 19, 2010.

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Copyright

   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
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   without warranty as described in the Simplified BSD License.

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/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.

Table of Contents

1. Introduction....................................................2
2. Terminology.....................................................3
3. Requirements for Graceful Shutdown..............................4
4. Mechanisms for Graceful Shutdown................................5
 4.1 OSPF/ ISIS Mechanisms for graceful shutdown...................5
 4.2 RSVP-TE Signaling Mechanisms for graceful shutdown............6
5. Manageability Considerations....................................7
6. Security Considerations.........................................8
7. IANA Considerations.............................................8
8. Acknowledgments.................................................8
9. Reference.......................................................8
 9.1 Normative Reference...........................................8
 9.2 Informative Reference.........................................8
10. Authors' Address:..............................................9

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

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   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 shutdown MPLS-TE/ GMPLS Traffic Engineering 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 shutdown. 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 single 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.

   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 Packets generated by ISIS routers and that
   contain routing information.

   LSA: Link State Advertisements generated by OSPF routers and that
   contain routing information.

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   TE-LSA/ TE-ISIS-LSP: The traffic engineering extensions to OSPF/
   ISIS.

   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.

   - 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.

   - 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.

   - It is desirable for new TE LSP setup 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.

   - 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.

   - It is required to give the ingress node the opportunity to take
   actions in order to reduce/eliminate traffic disruption on the TE
   LSPs that are using the network resources which are about to be
   shut down.

   - Graceful shutdown mechanisms are equally applicable to intra-
   domain and TE LSPs spanning multiple domains, as defined in
   [RFC4726]. Examples of such domains include IGP areas and
   Autonomous Systems.

   - Graceful shutdown is equally applicable to packet and non-
   packet networks.

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   - In order to make rerouting effective, it is required that when
     a node initiates the graceful shutdown of a resource, it
     identifies to all other network nodes the TE resource under
     graceful shutdown.
   - 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 prevent LSRs in a domain to use the
   resource being shut down.
   In addition, in order to discourage nodes from establishing new
   TE LSPs through the resources being shutdown, existing IGP
   mechanisms are used for the shutdown notification.

   A node where a link or the whole node is being shutdown 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/ ISIS Mechanisms for graceful shutdown

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

   The OSPF and ISIS procedures for graceful shutdown of TE links
   are similar to the graceful restart of OSPF and ISIS as described
   in [RFC4203] and [RFC5307], respectively. Specifically, the node
   where graceful shutdown of a link is desired originates the TE
   LSA/ISIS-LSP containing a Link TLV for the link under graceful
   shutdown with Traffic Engineering metric set to 0xffffffff, 0 as
   unreserved bandwidth, and if the TE link has LSC or FSC as its
   Switching Capability then also with 0 in the "Max LSP Bandwidth"
   field of the Interface Switching Capability Descriptor (ISCD)
   sub-TLV. A node may also specify a value which 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 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 graceful shutdown
   procedure is performed on a label resource within a TE Link, the

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   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 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 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 indicates 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 shutdown, 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].

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   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
   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
   shutdown. 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 PCE is used for path
   computation, head-end (or border) node acting as PCC specifies in
   its requests to the PCE that path computation should avoid the
   resource being gracefully shutdown. 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 head-end node or border node.

   If the node initiating the graceful shutdown procedure receives a
   path setup request for a new tunnel using resource being
   gracefully shutdown, it sends a Path Error 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 shutdown, the node initiating the
   graceful shutdown procedure may allow resource being gracefully
   shutdown to be 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 network to move
   traffic from the resource being shutdown. 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 showdown, a linkDown trap as defined in
   [RFC2863] should be generated for the TE link. Similarly, if a
   bundled TE links is being showdown, 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
   shutdown, a linkDown trap as defined in [RFC2863] should be
   generated for all TE links at the node.

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6. Security Considerations

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

   This document has no IANA actions.

8. 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.

9. Reference

9.1 Normative Reference

   [RFC2205] Braden, R. Ed. et al, "Resource ReSerVation Protocol
   (RSVP) Version 1, Functional Specification", RFC 2205.

   [RFC5710] Berger, L., Papadimitriou, D., and J. Vasseur,
   "PathErr Message Triggered MPLS and GMPLS LSP Reroute",
   RFC5710.

9.2 Informative Reference

   [RFC3209] Awduche D., Berger, L., Gan, D., Li T., Srinivasan, V.,
   Swallow, G., "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC
   3209.

   [RFC4736] Jean-Philippe Vasseur, et al "Reoptimization of MPLS
   Traffic Engineering loosely routed LSP paths", RFC 4736.

   [RFC3630] Katz D., Kompella K., Yeung D., "Traffic Engineering
   (TE) Extensions to OSPF Version 2", RFC 3630.

   [RFC5305] Smit, H. and T. Li, "Intermediate System to
   Intermediate System (IS-IS) Extensions for Traffic Engineering
   (TE)", RFC 5305.

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   [RFC4203] Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF
   Extensions in Support of Generalized Multi-Protocol Label
   Switching (GMPLS)", RFC 4203.

   [RFC5307]  Kompella, K., Ed., and Y. Rekhter, Ed., "Intermediate
   System to Intermediate System (IS-IS) Extensions in Support of
   Generalized Multi-Protocol Label Switching (GMPLS)", RFC 5307.

   [RFC3471]  Berger, L., "Generalized Multi-Protocol Label
   Switching (GMPLS) Signaling Functional Description", RFC 3471.

   [RFC3473]  Berger, L., "Generalized Multi-Protocol Label
   Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic
   Engineering (RSVP-TE) Extensions", RFC 3473.


   [RFC4726] Farrel A, Vasseur, J.-P., Ayyangar A., "A Framework for
   Inter-Domain MPLS Traffic Engineering", RFC 4726, November 2006.

   [RFC4201] Kompella, K., Rekhter, Y., Berger, L., "Link Bundling
   in MPLS Traffic Engineering", RFC 4201.

   [RFC4206] Kompella K., Rekhter Y., "Label Switched Paths (LSP)
   Hierarchy with Generalized Multi-Protocol Label Switching (GMPLS)
   Traffic Engineering (TE)", RFC 4206.

   [RFC4655] A. Farrel, J.-P. Vasseur, J. Ash, "A Path Computation
   Element (PCE)-Based Architecture", RFC 4655.

   [RFC2863] McCloghrie K., Kastenholz F., "The Interfaces Group
   MIB", RFC 2863.

   [MPLS-GMPLS-SECURITY] Luyuan F., Ed. "Security Framework for
   MPLS and GMPLS Networks", draft-ietf-mpls-mpls-and-gmpls-
   security-framework, work in progress.


10. Authors' Address:

   Zafar Ali
   Cisco systems, Inc.,
   2000 Innovation Drive
   Kanata, Ontario, K2K 3E8
   Canada.
   Email: zali@cisco.com

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   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
   jonathan.newton@cw.com































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