Networking Working Group
                                                               Zafar Ali
                                                   Jean-Philippe Vasseur
                                                             Anca Zamfir
                                                     Cisco Systems, Inc.

IETF Internet Draft
Category: Standard track
Expires: December 2006
                                                               June 2006


        Graceful Shutdown in GMPLS Traffic Engineering Networks

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   GMPLS-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. GMPLS-TE graceful shutdown mechanisms are
   tailored towards addressing the planned outage in the network.

   This document provides requirements and protocol mechanisms so as to
   reduce/eliminate traffic disruption in the event of a planned
   shutdown of a network resource. These operations are equally
   applicable for both MPLS and its GMPLS extensions.

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119 [i].

Table of Contents

1. Terminology........................................................2
2. Introduction.......................................................3
3. Requirements for Graceful Shutdown.................................3
4. Mechanisms for Graceful Shutdown...................................4
 4.1 RSVP-TE Signaling Mechanism for graceful shutdown...............4
 4.1.1 Graceful Shutdown of TE link(s)...............................5
 4.1.2 Graceful Shutdown of Component Link(s) in a Bundled TE Link...5
 4.1.3 Graceful Shutdown of TE Node..................................5
 4.2 OSPF/ ISIS Mechanisms for graceful shutdown.....................6
 4.2.1 Graceful Shutdown of TE link(s)...............................6
 4.2.2 Graceful Shutdown of Component Link(s) in a Bundled TE Link...6
 4.2.3 Graceful Shutdown of TE Node..................................6
5. Security Considerations............................................6
6. IANA Considerations................................................6
7. Intellectual Property Considerations...............................7
8. Full Copyright Statement...........................................7
9. Acknowledgments....................................................7
10. Reference.........................................................7
 10.1 Normative Reference............................................7
 10.2 Informative Reference..........................................8

1. Terminology

   LSR - Label Switching Device.

   LSP - An MPLS Label Switched Path

   Head-end or Ingress node: In this document the terms head-end node
   equally applies to the Ingress node that initiated signaling for the
                               [Page 2]

   Path, or an intermediate node (in the case of loose hops path
   computation) or a Path Computation Element (PCE) that computes the
   routes on behalf of its clients (PCC).

   GMPLS - The term GMPLS is used in this document to refer to both
   classic MPLS, as well as the GMPLS extensions to MPLS.

   TE Link - The term TE link refers to a physical link or an FA-LSP, on
   which traffic engineering is enabled. A TE link can be bundled or

   The terms node and LSR will be used interchangeably in this document.

2. 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 definitely) disable Traffic Engineering on 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 GMPLS traffic engineered flows carried
   over TE LSPs in the network by triggering notifications so as to
   graceful reroute such flows before the administrative procedures are

   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 SHOULD delay the removal
   of the resources for forwarding, for some period determined by local
   policy. This is to allow control plane to gracefully divert the
   traffic away from the resource being gracefully shutdown. Similarly,
   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 at a node.

   This document describes the mechanisms that can be used to gracefully
   shutdown 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 traditional shutdown
   operation of an interface, but it is a separate step that is taken
   before the IGP on the link is brought down and before the interface
   is brought down at different layers. This document only addresses TE
   node and TE resources.

3. Requirements for Graceful Shutdown

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This section lists the requirements for graceful shutdown in the
context of GMPLS Traffic Engineering.

   - Graceful shutdown must 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 or an entire node.

   - It is required to prevent other network nodes to use the network
   resources that are about to be shutdown, should new TE LSP be set up.
   Similarly it is required to reduce/eliminate traffic disruption on
   the LSP(s) using the network resources which are about to be

   - Graceful shutdown mechanisms are required to address TE LSPs
   spanning multiple domains, as well as intra domain TE LSPs. Here, a
   domain is defined as either an IGP area or an Autonomous System

   - 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 to communicate
   information about the TE resource under graceful shutdown.

4. Mechanisms for Graceful Shutdown

   An IGP only based solution is 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, it must be noted that 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.

4.1 RSVP-TE Signaling Mechanism 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. The Graceful Shutdown mechanism
   outlined in the following section, uses Path Error and where
   available, Notify message, in order to achieve this requirement. Such
   mechanisms relying on signaling are only applicable to the existing
   Setup request for new LSPs over the TE resource being gracefully
   shutdown SHOULD be rejected using the existing mechanisms that are
   applied when the TE resource is not available.

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4.1.1 Graceful Shutdown of TE link(s)

   The node where graceful shutdown of a link or a set of links is
   desired MUST trigger a Path Error message with ‘‘local link
   maintenance required’’ sub-code for all affected LSPs. The ‘‘local TE
   link maintenance required’’ error code is defined in [PATH-REOPT]. If
   available, and where notify requests were included when the LSPs were
   initially setup, Notify message (as defined in []) MAY also be used
   for delivery of this information to the head-end nodes.

   When a head-end LSR receives a Path Error (or Notify) message with
   sub-code "Local Maintenance on TE Link required Flag", it SHOULD
   immediately trigger a make-before-break procedure. A head-end node
   SHOULD avoid the IP address contained in the PathErr (or Notify
   message) when performing path computation for the new LSP.

4.1.2 Graceful Shutdown of Component Link(s) in a Bundled TE Link

   MPLS TE Link Bundling [BUNDLE] requires that an LSP is pinned down to
   component link(s). Hence, when a component link is shutdown, the TE
   LSPs affected by such maintenance action needs to be resignaled.

   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 TE links may still be able to
   admit new LSPs. Consequently a new error sub-code for PathError and
   Notify message is needed:

         9 (TBA)      Local component link maintenance required

   Error Sub-code for ‘‘Local component link maintenance required’’ is to
   be assigned by IANA.

   If the last component link is being shutdown, the procedure outlined
   in Section 5.1 is used.

   When a head-end LSR receives an RSVP Path Error or Notify message
   with sub-code "local component link maintenance required’’ Flag set,
   it SHOULD immediately perform a make-before-break to avoid traffic
   loss. The head-end LSR MAY still use the IP address contained in the
   Path Error or Notify message in performing path computation for
   rerouting the LSP. This is because, this address is an IP address of
   the component link and the flag is an implicit indication that the TE
   link may still have capacity to admit new LSPs. However, if the ERO
   is computed such that it also provides details of the component link
   selection(s) along the Path, the component link selection with IP
   address contained in the Path Error or Notify message SHOULD be

4.1.3 Graceful Shutdown of TE Node

                               [Page 5]

   When graceful shutdown at node level is desired, the node in question
   follows the procedure specified in the previous section for all TE

4.2 OSPF/ ISIS Mechanisms for graceful shutdown

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

4.2.1 Graceful Shutdown of TE link(s)

   The node where graceful-shutdown of a link is desired MUST originate
   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.  This
   would discourage new LSP establishment through the link under
   graceful shutdown.

   Neighbors of the node where graceful shutdown procedure is in
   progress SHOULD continue to advertise the actual unreserved bandwidth
   of the TE links from the neighbors to that node, without any routing
   adjacency change.

4.2.2 Graceful Shutdown of Component Link(s) in a Bundled TE Link

   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. If the removal of the component link 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 outlined in Section 4.2.1 is used.

4.2.3 Graceful Shutdown of TE Node

   When graceful shutdown at node level is desired, the node in question
   follows the procedure specified in the previous section for all TE

5. Security Considerations

   This document does not introduce new security issues. The security
   considerations pertaining to the original RSVP protocol [RSVP] remain

6. IANA Considerations

   A new error sub-code for Path Error and Notify message is needed for
   ‘‘Local component link maintenance required’’ flag.

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7. Intellectual Property Considerations

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at

8. Full Copyright Statement

   Copyright (C) The Internet Society (2006). This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.

   This document and the information contained herein are provided on an

9. Acknowledgments

The authors would like to acknowledge useful comments from David Ward,
Sami Boutros, Adrian Farrel and Dimitri Papadimitriou.

10. Reference

10.1 Normative Reference

   [RSVP] Braden, et al, "Resource ReSerVation Protocol (RSVP) - Version
   1, Functional Specification", RFC 2205, September 1997.

    [RSVP-TE] Awduche, et al, "Extensions to RSVP for LSP Tunnels", RFC
   3209, December 2001.

                               [Page 7]

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

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

   [RFC4203] K. Kompella, Y. Rekhter, et al, ‘‘OSPF Extensions in Support
   of Generalized MPLS’’, draft-ietf-ccamp-ospf-gmpls-extensions-12.txt.

   [RFC4205] K. Kompella, Y. Rekhter, et al, ‘‘IS-IS Extensions in
   Support of Generalized MPLS’’, draft-ietf-isis-gmpls-extensions-

   [PATH-REOPT] Jean-Philippe Vasseur, and Y. Ikejiri, ‘‘Reoptimization
   of MPLS Traffic Engineering loosely routed LSP paths’’, draft-ietf-

10.2 Informative Reference

   [INTER-AREA-AS] Adrian Farrel, Jean-Philippe Vasseur, Arthi Ayyangar,
   ‘‘A Framework for Inter-Domain MPLS Traffic Engineering’’, draft-ietf-

   [BUNDLE] Kompella, K., Rekhter, Y., Berger, L., "Link Bundling in
   MPLS Traffic Engineering", draft-ietf-mpls-bunle-04.txt (work in

Authors' Address:

Zafar Ali
Cisco systems, Inc.,
2000 Innovation Drive
Kanata, Ontario, K2K 3E8

Jean Philippe Vasseur
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough , MA - 01719

Anca Zamfir
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario, K2K 3E8

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