RFC 5817
Graceful Shutdown in MPLS and Generalized MPLS Traffic Engineering Networks
RFC 5817: Graceful Shutdown in MPLS and Generalized MPLS Traffic Engineering Networks 🎀
Okay bestie, let's get into RFC 5817 💖 It's an IETF (Internet Engineering Task Force) document, and it's labelled Category: Informational with ISSN 2070-1721. It was published in April 2010 and written by Z. Ali, JP. Vasseur, and A. Zamfir from Cisco Systems, Inc., plus J. Newton from Cable and Wireless. The title block doesn't have an Obsoletes or Updates line, so it isn't replacing or changing any other RFC 🧚
Abstract ✨
So, MPLS-TE Graceful Shutdown is a way to explicitly tell the nodes in a Traffic Engineering (TE) enabled network that TE is about to be turned off on a link or on a whole Label Switching Router (LSR) 🌸 It's built for planned outages, so nothing gets dropped by surprise.
This document gives requirements and protocol mechanisms to reduce or eliminate traffic disruption when a network resource is planned to be shut down 💅 These operations work the same for both MPLS-TE and its Generalized MPLS (GMPLS) extensions, so you get the same glow-up either way 🦋
Status of This Memo ✨
Okay so this one is not an Internet Standards Track specification. It's published for informational purposes 🎀
It's a product of the IETF, and it represents the consensus of the IETF community 👑 It went through public review and was approved for publication by the Internet Engineering Steering Group (IESG). Not every IESG-approved document is a candidate for any level of Internet Standard, so check Section 2 of RFC 5741 if you want the full story 🫶
For the current status, errata, and how to send feedback, go to 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, which you can find at http://trustee.ietf.org/license-info, as they stand on the date of publication. Please read them carefully, because they explain your rights and restrictions for this document 🙈 Any Code Components pulled out of this document must include the Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come without warranty, as the Simplified BSD License describes 💀
This document may contain material from IETF Documents or IETF Contributions that were published or made publicly available before November 10, 2008. The people controlling the copyright in some of that material may not have given the IETF Trust permission to allow modifications outside the IETF Standards Process 😭 Unless you get an adequate license from those copyright holders, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be made outside the IETF Standards Process. The only exceptions are formatting it for publication as an RFC or translating 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 .....................................91. Introduction 🦋
Okay so when outages are planned, like for maintenance, you can use some mechanisms to avoid traffic disruption 🌸 That's different from an unplanned network element failure, where recovery mechanisms can keep disruption to a minimum but usually can't avoid it entirely 😭 That's why a Service Provider may want to gracefully (temporarily or indefinitely) remove a TE link, a group of TE links, or an entire node for administrative reasons, like link maintenance, a software or hardware upgrade at a node, or significant TE configuration changes ✨ In all of these cases the goal is the same: keep the impact on traffic carried over TE LSPs as low as possible by sending notifications that gracefully reroute those flows before the administrative procedures start 💅
These operations are equally applicable to both MPLS-TE [RFC3209] and its Generalized MPLS (GMPLS) extensions [RFC3471] [RFC3473] 🎀
This document describes the mechanisms you can use to gracefully shut down MPLS-TE / GMPLS-TE on a resource, like 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 take several steps. These steps fall into two broad sets: disabling the resource in the control plane, and disabling the resource in the data plane 💖 The node starting the graceful shutdown adds a delay between the two sets, so the control plane has time to gracefully divert traffic away from the resource being shut down 🫶 What triggers the graceful shutdown event is a local matter for the node that starts it. Usually it's triggered for administrative reasons, like link maintenance or a software or hardware upgrade 🌈
2. Terminology 💜
- LSR: Label Switching Router. The terms node and LSR are used interchangeably in this document.
- GMPLS: In this document, the term GMPLS refers 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.
- 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 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 can't be found after removing a resource (for example, a TE link or TE node), that resource is called "last resort" for reaching 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 started 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 need the resource because of local constraints, is required to be rejected as if the resource were unavailable 🙈
- 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 🦋
- If the resource being shut down is a last-resort resource, based on a local decision, the node starting the graceful shutdown procedure can cancel the shutdown operation 🌈
- It is required to give the ingress node the opportunity to take actions that reduce or eliminate traffic disruption on the TE LSPs using the network resources that are about to be shut down 🫶
- Graceful shutdown mechanisms are equally applicable to intra-domain TE LSPs and to 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 starts 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, for example 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] isn't applicable when dealing with inter-area and inter-AS traffic engineering, because IGP flooding is restricted to IGP areas/levels 😭 So this document proposes an RSVP-based solution to handle TE LSPs that span multiple domains 🎀 On top of that, to discourage nodes from setting up 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 described in Section 4.1. Then, after some delay to allow the network to converge, it uses the signaling mechanism described in Section 4.2 🌸
4.1. OSPF / IS-IS Mechanisms for Graceful Shutdown
okay so this section is all about reusing the OSPF and IS-IS tools that already exist for graceful shutdown in GMPLS networks 🦋
The OSPF and IS-IS graceful shutdown moves for TE links are basically a sibling of graceful restart in OSPF and IS-IS, which are described in [RFC4203] and [RFC5307] respectively. Here's the vibe: the node that wants to shut a link down originates the TE LSA or IS-IS-LSP with a Link TLV for that link under graceful shutdown. The Traffic Engineering metric is set to 0xffffffff, and unreserved bandwidth is 0 💅 If the TE link has LSC or FSC as its Switching Capability, it also has 0 in the "Max LSP Bandwidth" field of the Interface Switching Capability Descriptor (ISCD) sub-TLV. A node may also put a value that's greater than the available bandwidth in the "Minimum LSP bandwidth" field of that same ISCD sub-TLV. This would discourage new TE LSP establishment through the link under graceful shutdown 🙈
If graceful shutdown is performed on a component link inside a TE link bundle, and it's not the last component link available in that TE link, the link attributes of the TE link get recomputed ✨ Same deal if the shutdown is performed on a label resource within a TE link: the link attributes get recomputed. If removing the component link or label resource causes a significant bandwidth change event, a new LSA gets originated with the new traffic parameters. And if the last component link is the one being shut down, the routing procedure related to TE link removal is used instead 🔥
Neighbors of the node that's going through graceful shutdown keep advertising the actual unreserved bandwidth of the TE links from them to that node. There's no routing adjacency change, so nobody panics 🌸
When graceful shutdown at node level is desired, the node in question follows the procedure from the previous section for all of its TE links. 👑
4.2 RSVP-TE Signaling Mechanisms for Graceful Shutdown ✨
okay remember Section 3? One of the signaling requirements there was carrying information about the resource under graceful shutdown. To make that happen, the graceful shutdown procedure uses the TE LSP rerouting mechanism defined in [RFC5710] 🧚
Here's how it plays out. The node where graceful shutdown of an unbundled TE link, or of an entire bundled TE link, is desired triggers a PathErr message with the error code Notify and the error value Local link maintenance required, for all affected TE LSPs. Similarly, the node that's being gracefully shut down triggers a PathErr message with the error code Notify and the 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. Either way, it's the address and TLVs carried by the ERROR_SPEC object, not the error value, that tell you which resource is being gracefully shut down 💖
Bundling is where things get spicy 🌶️ MPLS-TE link bundling [RFC4201] requires that a TE LSP is pinned down to a component link. So graceful shutdown of a component link in a bundled TE link is different from graceful shutdown of an unbundled TE link or an entire bundled TE link. When only a subset of the component links is being shut down, and not the entire bundled TE link, the remaining component links 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 the error value Local link maintenance required. The rest of the ERROR_SPEC object is built using the Component Reroute Request procedure defined in [RFC5710] 🍓
If graceful shutdown of a label resource is desired, the node starting this triggers a PathErr message with the error codes and error values Notify/Local link maintenance required. The rest of the ERROR_SPEC object is built using the Label Reroute Request procedure defined in [RFC5710] 💜
When a head-end node, a transit node, or a border node gets a PathErr message with the error code Notify and the error value Local link maintenance required or Local node maintenance required, it follows the procedures in [RFC5710] to reroute traffic around the resource being gracefully shut down. When computing a path for the new TE LSP, the head-end node or border node avoids using the TE resources identified by the ERROR_SPEC object. If a PCE is used for path computation, the head-end (or border) node acting as PCC tells the PCE in its requests that the path computation should avoid the resource being gracefully shut down. How long the head-end node or border node avoids the TE resources identified by the IP address in the PathErr is a local decision at that node ⏳
Now, if the node starting graceful shutdown gets a path setup request for a new tunnel that wants to use the resource being gracefully shut down, it sends a PathErr message with the Notify error code in the ERROR SPEC object, plus an error value that matches the type of resource being shut down 🙅♀️ But here's the twist: based on a local decision, if an existing tunnel is still using that resource, the node can allow it to be used as a "last resort". The node can tell new tunnels apart from existing ones by inspecting the SENDER TEMPLATE and SESSION objects 🕵️♀️
If the resource being shut down is a last-resort resource, it can be used. In other words, based on a local decision, the node starting graceful shutdown can cancel the shutdown operation. Also, based on a local decision, it can delay the actual removal of the resource for forwarding. That gives the network time to move traffic off the resource being shut down. For this purpose, the node starting graceful shutdown 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 that 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, and also for each of its component links. And if a TE node is being shut down, a linkDown trap as defined in [RFC2863] should be generated for all TE links at that node 🔔
6. Security Considerations 🔐
okay this one is important, bestie. Read it properly 💀
This document introduces no new security considerations, since it just describes the usage of existing formats and mechanisms. It relies on existing procedures for advertising TE LSA / IS-IS-LSPs that contain Link TLVs. Tampering with TE LSAs / IS-IS-LSPs may affect traffic engineering computations, so it's suggested that any mechanisms used for securing the transmission of normal LSAs / IS-IS-LSPs also get applied equally to all Opaque LSAs / IS-IS-LSPs that this document uses. The existing security considerations specified in [RFC3630], [RFC5305], [RFC4203], [RFC5307], and [MPLS-GMPLS-SEC] remain relevant and are sufficient. On top of that, the Security Considerations section in [RFC5710] and section 9 of [RFC4736] should be used to understand the security considerations for 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 🌈
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.
[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.Authors' Addresses ✨
Okay bestie, here are the authors and how to reach them 💌 Zafar, Jean Philippe, Anca, and Jonathan all helped put this together 🫶
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.comThat's the whole thing, bestie! 🌈💖 Go slay your next network 🧚👑
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- ietf: rfc5817 2010-04
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