Network
CCAMP Working Group                                         Z. Ali
Internet Draft                                           JP.
                                                           Zafar Ali
                                               Jean-Philippe Vasseur
Category: Informational                                    A.
                                                         Anca Zamfir
Creater: October 29, 2008
                                                 Cisco Systems, Inc.
Expires: April 29, 2009                                    J.
                                                     Jonathan Newton
                                                  Cable and Wireless

Category: Informational
Expires: September 08, 2009                           March 09, 2009

           draft-ietf-ccamp-mpls-graceful-shutdown-09.txt

           Graceful Shutdown in MPLS and Generalized MPLS
                    Traffic Engineering Networks

           draft-ietf-ccamp-mpls-graceful-shutdown-08.txt

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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 and its Generalized MPLS (GMPLS)
   extensions.

Table of Contents

1. Introduction....................................................2
2. Terminology.....................................................3
3. Requirements for Graceful Shutdown..............................3
4. Mechanisms for Graceful Shutdown................................4
4.1 OSPF/ ISIS Mechanisms for graceful shutdown..................5 shutdown....................5
 4.2 RSVP-TE Signaling Mechanisms for graceful shutdown...........6 shutdown............6
5. Security Considerations.........................................8 Considerations.........................................7
6. IANA Considerations.............................................8 Considerations.............................................7
7. Acknowledgments.................................................8 Acknowledgments.................................................7
8. Reference.......................................................9 Reference.......................................................8
 8.1 Normative Reference..........................................9 Reference...........................................8
 8.2 Informative Reference........................................9 Reference.........................................8
9. Authors' Addresses.............................................10 Address:...............................................9
10. Intellectual Property Considerations..........................11
   11. Disclaimer of Validity........................................11
   12. Copyright Statement...........................................11 Notice..............................................10
11. Legal.........................................................10

1. Introduction

   When outages in a network are planned (e.g. for maintenance
   purpose), 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. Hence, 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 [RFC3209]
   and its Generalized MPLS (GMPLS) extensions. extensions [RFC3471], [RFC3473].

   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 removing the resource for
   forwarding. The node initiating the graceful shutdown condition
   is expected to introduce a delay between disabling the resource
   in the control plane and removing the resource for forwarding.
   This is 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.

   This document describes the mechanisms that can be used to
   gracefully shutdown MPLS/ GMPLS Traffic Engineering on a
   resource. As mentioned earlier, the graceful shutdown of the
   Traffic Engineering capability on a resource could be
   incorporated in the shutdown operation of an interface, but it is
   such as a separate step that is taken before the IGP on the TE link, a component link is
   brought down and before the interface is brought down at
   different layers. This document only addresses within a bundled TE nodes and link, a
   label resource or an entire TE
   resources. node.

2. Terminology

   Border node: Ingress

   LSR of an LSP segment (S-LSP).

   GMPLS: - 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.

   LSP - An MPLS-TE/ GMPLS-TE Label Switched Path.

   Head-end node: Ingress LSR that initiated signaling for the Path.

   Last resort resource: If a path to a destination from a given
   head-end node cannot be found upon removal

   Border node: Ingress LSR 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.

   LSP: An MPLS-TE/ GMPLS-TE Label Switched Path.

   LSR: Label Switching Router. The terms node and LSR are used
   interchangeably in this document. an LSP segment (S-LSP).

   Path Computation Element (PCE): An entity that computes the
   routes on behalf of its clients (PCC).

   TE Link: Link - The term TE link refers to single or a bundle of
   physical link(s) or FA-LSP(s) on which traffic engineering is
   enabled [RFC4206], [RFC4201].

   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 Traffic Engineering.

   - 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 resource(s) 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 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 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 shutdown is a last resort, it can be
   used. Time or decision for removal of the resource being shutdown
   is based on a local decision at the node initiating the graceful
   shutdown procedure.

   - It is required to give the ingress node the opportunity to take
   actions in order to reduce/eliminate traffic disruption on the
   LSP(s) that are using the network resources which are about to be
   shutdown.

   - Graceful shutdown mechanisms are equally applicable to intra-
   domain and TE LSPs spanning multiple domains. Here, a domain is
   defined as either an IGP area or an Autonomous System [RFC4726].

   - Graceful shutdown is equally applicable to GMPLS-TE, as well as
   packet-based (MPLS) TE LSPs.

   - 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
     shutdown 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] are not applicable when dealing with Inter-area and
   Inter-AS traffic engineering, as IGP LSA/LSP flooding is
   restricted to IGP areas/levels. Consequently, RSVP based
   mechanisms are required to cope with TE LSPs spanning multiple
   domains. At the same time, RSVP mechanisms only convey the
   information for the transiting LSPs to the router along the
   upstream Path and not to all nodes in the network. Furthermore,
   graceful shutdown notification via IGP flooding is required to
   discourage a node from establishing new LSPs through the
   resources being shutdown. In the following sections the
   complementary mechanisms for RSVP-TE and IGP for Graceful
   Shutdown are described.

   A node where a link or the whole node is being shutdown may first
   trigger the IGP updates as described in Section 4.1, introduce a
   delay to allow network convergence and only then use the
   signaling mechanism described in Section 4.2.

4.1 OSPF/ ISIS Mechanisms for graceful shutdown

   The procedures provided in this section are equally applicable to
   OSPF and ISIS.

   OSPF and ISIS procedure for graceful shutdown of TE link(s) is
   similar to 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/LSP containing Link TLV for the link under graceful shutdown
   with Traffic Engineering metric set to 0xffffffff, 0 as
   unreserved bandwidth, and if the link has LSC or FSC as its
   Switching Capability then also with 0 as Max LSP Bandwidth. A
   node may also specify a value for Minimum LSP bandwidth which is
   greater than the available bandwidth. This would discourage new
   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
   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
   shutdown, the routing procedure related to TE link removal is
   used.

   Neighbors of the node where graceful shutdown procedure is in
   progress continues 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 LSP rerouting mechanism as defined in
   [LSP-REROUTE].

   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 "Reroute" codes and an error value values of "TE "Notify/Local
   link Graceful Shutdown required" maintenance required", for all affected LSPs. Similarly, the
   node that is being gracefully shutdown triggers a PathErr message
   with the error code "Reroute" codes and an error value values of "Node Graceful Shutdown required" "Notify/ Local node
   maintenance required", for all 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 shutdown.

   MPLS TE Link Bundling [RFC4201] requires that an 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 TE bundled link is being shutdown, the
   remaining component links of the bundled TE link may still be
   able to admit new LSPs. The node where graceful shutdown of a
   component link is desired triggers a PathErr message with the
   error code "Reroute" codes and the new error value values of "Component "Notify/Local link
   Graceful Shutdown required" for all affected LSPs. maintenance
   required". The PathErr
   message includes in rest of the ERROR_SPEC the TE Link ID address. If the
   last component link object is being shutdown, constructed using
   Component Reroute Request procedure for gracefully
   shutdown entire bundled TE link outlined above is be used,
   instead. defined in [LSP-REROUTE].

   If graceful shutdown of a label resource is desired, the node
   initiating this action triggers a PathErr message with the error
   code "Reroute"
   codes and the new error value values of "Label resource
   Graceful Shutdown required" for the affected LSP. "Notify/Local link maintenance
   required". The PathErr
   message includes in rest of the ERROR_SPEC the TE Link ID address.

   The "Reroute" error code for the ERROR SPEC object is constructed using
   Label Reroute Request procedure defined in [LSP-REROUTE]. This document defines following four

   When a head-end node, or a transit node (including border node)
   receives a PathErr message with error value
   for the "Reroute" codes and error code [To Be Confirmed (TBC) by IANA upon
   publication values of this document]:

   Error-value  Meaning                                    Reference
   2 (TBC)      Node Graceful Shutdown required            This doc
   3 (TBC)      TE link Graceful Shutdown required         This doc
   4 (TBC)      Component link Graceful Shutdown required  This doc
   5 (TBC)      Label resource Graceful Shutdown required  This doc
   The PathErr message includes in the ERROR_SPEC the TE Link ID
   address.

   If unbundled TE link, component link of a bundled TE link, entire
   bundled TE link, or label resource of a TE link is being
   gracefully shutdown, the PathErr message includes the ERROR_SPEC
   object containing IP address of the TE Link being gracefully
   shutdown. If TE
   "Notify/Local link is unnumbered, the PathErr message includes
   the ERROR_SPEC object containing unnumbered ID and TE node ID for
   the TE Link being gracefully shutdown. Similarly, if the TE node
   is being gracefully shutdown, the PathErr message includes in the
   ERROR_SPEC object the MPLS-TE node ID address.

   When a head-end node, or border node receives a PathErr message
   with "Reroute" error code and error value of "Node Graceful
   Shutdown maintenance required" or "TE link Graceful Shutdown required", or
   "Component link Graceful Shutdown "Notify/ Local node
   maintenance required", or "Label resource
   Graceful Shutdown required" it follows the procedures make-before-break procedure
   defined in
   [LSP-REROUTE]. [LSP-REROUTE] to reroute the traffic around the
   resource being gracefully shutdown. When performing path
   computation for the new LSP, the head-end node, or border node
   avoids using the TE resources identified by the IP address contained in the PathErr. ERROR_SPEC
   object. If PCE is used for path computation, head-end node or
   border node acts as PCC to request the PCE via PCEP for path
   computation avoiding resource being gracefully shutdown. The
   amount of time the head-
   end head-end node, or border node avoid 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 node initiating the graceful shutdown procedure received path
   setup request for a new tunnel using resource being gracefully
   shutdown, it sends a Path Error message with "Reroute" "Notify" error code
   in the ERROR SPEC object and an error value consistent with the
   type of resource being gracefully shutdown. 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 received path setup request for an existing tunnel, it may allow signaling for it. This is to 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 based on the tunnel ID in the SESSION object.

   Time or decision for removal of the resource being shutdown from
   forwarding is based on a local decision at the node initiating
   the graceful shutdown procedure. For this purpose, the node
   initiating graceful shutdown procedure follows the Reroute
   Request Timeout procedure defined in [LSP-REROUTE].

5. Security Considerations

   This document introduces two no new error values for "Reroute" error
   code security considerations as this
   document describes usage of the ERROR SPEC object defined in [LSP-REROUTE]. existing formats and mechanisms. This
   document also introduces ways to make resources unavailable for
   the control plane. It is therefore recommended that procedures in
   [RFC2747], which provides mechanisms to protect against external
   agents compromising the RSVP signaling state in an RSVP agent, be
   used.  Specifically, [RFC2747] mechanisms provide some degree of
   protection to the head-end node or border node RSVP agent against
   making resources unavailable for control plan from an external
   agent sending Path Error messages with existing or new error code
   and error values. In summary, existing security considerations
   specified in [LSP-REROUTE], [RFC2747], [RFC2205], [RFC3209],
   [RFC4736], [RFC3471], [RFC3473] and [MPLS-GMPLS-SECURITY] remain
   relevant and suffice.

   This document relies on existing relies on existing procedures for advertisement of TE
   LSA/LSP containing Link TLV. Tampering with TE LSAs may have an
   effect on traffic engineering computations, and it is suggested
   that any mechanisms used for securing the transmission of normal
   OSPF LSAs/ ISIS LSPs be applied equally to all Opaque LSAs/ LSPs
   this document uses.  In summary, existing  Existing security considerations specified
   in [RFC3630], [RFC5305], [RFC4203], [RFC5307] and [MPLS-GMPLS-SECURITY] [MPLS-GMPLS-
   SECURITY] remain relevant and suffice.

6. IANA Considerations

   The "Reroute" error code Furthermore, security
   considerations section in [LSP-REROUTE] and the Section 9 of
   [RFC4736] should be used for understanding the ERROR SPEC object is defined security
   considerations related to the formats and mechanisms used in
   [LSP-REROUTE]. this
   document.

6. IANA Considerations

   This document defines following four error value
   for the "Reroute" error code [To Be Confirmed (TBC) by has no IANA upon
   publication of this document]:

   Error-value  Meaning                                   Reference
   2 (TBC)      Node Graceful Shutdown required            This doc
   3 (TBC)      TE link Graceful Shutdown required         This doc
   4 (TBC)      Component link Graceful Shutdown required  This doc
   5 (TBC)      Label resource Graceful Shutdown required  This doc actions.

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.

8. Reference

8.1 Normative Reference

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

   [LSP-REROUTE] Berger, L., Papadimitriou, D., and J. Vasseur,
   "PathErr Message Triggered MPLS and GMPLS LSP Reroute", draft-
   ietf-mpls-gmpls-lsp-reroute (work in progress).

8.2 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, December 2001.
   3209.

   [RFC4736] Jean-Philippe Vasseur, et al "Reoptimization of MPLS
   Traffic Engineering loosely routed LSP paths", RFC 4736,
             November 2006.

   [LSP-REROUTE] Berger, L., Papadimitriou, D., and J. Vasseur,
             "PathErr Message Triggered MPLS and GMPLS LSP Reroute",
             draft-ietf-mpls-gmpls-lsp-reroute, work in progress.

8.2 Informative Reference

   [RFC2205] Braden, R. Ed. et al, "Resource ReSerVation Protocol (RSVP)
             Version 1, Functional Specification", RFC 2205, December
             1997.

   [RFC2747] Baker, F., Lindell, B., and M. Talwar, "RSVP Cryptographic
             Authentication", RFC 2747, January 2000.

   [RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching
             (GMPLS) Signaling Functional Description", RFC 3471,
             January 2003.

   [RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching
             (GMPLS) Signaling Resource ReserVation Protocol-Traffic
             Engineering (RSVP-TE) Extensions", RFC 3473, January 2003. 4736.

   [RFC3630] Katz D., Kompella K., Yeung D., "Traffic Engineering
   (TE) Extensions to OSPF Version 2", RFC 3630, September
             2003.

   [RFC4201] Kompella, K., Rekhter, Y., Berger, L., "Link Bundling in
             MPLS Traffic Engineering", RFC 4201, October 2005.

   [RFC4203] Kompella, K., Ed., 3630.

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

   [RFC4203] Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF
   Extensions in Support of Generalized Multi-Protocol Label
   Switching (GMPLS)", RFC 4203, October 2005.

   [RFC4206] Kompella 4203.

   [RFC5307]  Kompella, K., Rekhter Y., "Label Switched Paths (LSP)
             Hierarchy with 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) Traffic Signaling Functional Description", RFC 3471.

  [RFC3473]  Berger, L., "Generalized Multi-Protocol Label
   Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic
   Engineering (TE)", (RSVP-TE) Extensions", RFC 4206, October 2005. 3473.

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

   [RFC5305] Smit, H. and T. Li, "Intermediate System to Intermediate
             System (IS-IS) Extensions for Traffic Engineering (TE)",
             RFC 5305, October 2008.

   [RFC5307]

   [RFC4201] Kompella, K., Ed., and Y. Rekhter, Ed., "Intermediate
             System to Intermediate System (IS-IS) Extensions Y., Berger, L., "Link Bundling
   in
             Support of MPLS Traffic Engineering", RFC 4201.

   [RFC4206] Kompella K., Rekhter Y., "Label Switched Paths (LSP)
   Hierarchy with Generalized Multi-Protocol Label Switching
             (GMPLS)", (GMPLS)
   Traffic Engineering (TE)", RFC 5307, October 2008. 4206.

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

9. Authors' Addresses Address:

   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
   jonathan.newton@cw.com

10. Intellectual Property Considerations

   The Copyright Notice

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   This document documents and the information contained herein therein are provided
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