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
AbstractMPLS-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.
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. 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
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.
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.
- 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 or eliminate traffic disruption on the TE LSPs that are using the network resources that are about to be shut down. - 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. - Graceful shutdown is equally applicable to packet and non-packet networks. - 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. - 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. 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.
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. 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
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
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]. 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. 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.
[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. [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.
[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.