Networking Working Group
Zafar Ali
Jean-Philippe Vasseur
Anca Zamfir
Cisco Systems, Inc.
IETF Internet Draft
Category: Standard track
Expires: December 2006
June 2006
draft-ali-ccamp-mpls-graceful-shutdown-04.txt
Graceful Shutdown in GMPLS Traffic Engineering Networks
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Abstract
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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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
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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
unbundled.
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
started.
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
shutdown.
- 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
[INTER-AREA-AS].
- 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
LSPs.
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 荘local link
maintenance required鋳 sub-code for all affected LSPs. The 荘local TE
link maintenance required鋳 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 荘Local component link maintenance required鋳 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鋳 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
avoided.
4.1.3 Graceful Shutdown of TE Node
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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 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
Links.
5. Security Considerations
This document does not introduce new security issues. The security
considerations pertaining to the original RSVP protocol [RSVP] remain
relevant.
6. IANA Considerations
A new error sub-code for Path Error and Notify message is needed for
荘Local component link maintenance required鋳 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
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specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
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
ietf-ipr@ietf.org.
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
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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.
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[RFC3471] Generalized Multi-Protocol Label Switching (GMPLS)
Signaling Functional Description, RFC 3471, L. Berger, et al, January
2003.
[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, 荘OSPF Extensions in Support
of Generalized MPLS鋳, draft-ietf-ccamp-ospf-gmpls-extensions-12.txt.
[RFC4205] K. Kompella, Y. Rekhter, et al, 荘IS-IS Extensions in
Support of Generalized MPLS鋳, draft-ietf-isis-gmpls-extensions-
19.txt.
[PATH-REOPT] Jean-Philippe Vasseur, and Y. Ikejiri, 荘Reoptimization
of MPLS Traffic Engineering loosely routed LSP paths鋳, draft-ietf-
ccamp-loose-path-reopt-02.txt.
10.2 Informative Reference
[INTER-AREA-AS] Adrian Farrel, Jean-Philippe Vasseur, Arthi Ayyangar,
荘A Framework for Inter-Domain MPLS Traffic Engineering鋳, draft-ietf-
ccamp-inter-domain-framework-04.txt.
[BUNDLE] Kompella, K., Rekhter, Y., Berger, L., "Link Bundling in
MPLS Traffic Engineering", draft-ietf-mpls-bunle-04.txt (work in
progress)
Authors' 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
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