One document matched: draft-ietf-ccamp-mpls-graceful-shutdown-05.txt
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Networking Working Group
Internet Draft
Zafar Ali
Jean-Philippe Vasseur
Anca Zamfir
Cisco Systems, Inc.
Jonathan Newton
Cable and Wireless
Category: Informational
Expires: July 2008 January 2008
draft-ietf-ccamp-mpls-graceful-shutdown-05.txt
Graceful Shutdown in MPLS and Generalized MPLS
Traffic Engineering Networks
Status of this Memo
By submitting this Internet-Draft, each author represents that
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aware have been or will be disclosed, and any of which he or she
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This Internet-Draft will expire on July 2008.
Copyright Notice
Copyright (C) The IETF Trust (2008).
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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.
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 [RFC2119].
Table of Contents
1. Terminology.....................................................3
2. Introduction....................................................3
3. Requirements for Graceful Shutdown..............................4
4. Mechanisms for Graceful Shutdown................................5
4.1 OSPF/ ISIS Mechanisms for graceful shutdown....................5
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.................................6
4.1.4 Graceful Shutdown of Label Resource..........................6
4.2 RSVP-TE Signaling Mechanism 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 .7
4.2.3 Graceful Shutdown of TE Node.................................8
4.2.2 Graceful Shutdown of a Label Resource........................8
5. Security Considerations.........................................8
6. IANA Considerations.............................................9
7. Acknowledgments.................................................9
8. Reference.......................................................9
8.1 Normative Reference............................................9
8.2 Informative Reference..........................................9
9. Authors' Address:..............................................10
10. Intellectual Property Considerations..........................10
11. Disclaimer of Validity........................................11
12. Copyright Statement...........................................11
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1. Terminology
LSR (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.
Border node: Ingress LSR of an LSP segment (S-LSP).
Path Computation Element (PCE): An entity that computes the
routes on behalf of its clients (PCC).
TE 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].
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)
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 GMPLS traffic engineered flows carried
over TE LSPs in the network by triggering notifications so as to
gracefully 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 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.
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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
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 nodes and TE resources.
3. Requirements for Graceful Shutdown
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.
- 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, must 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
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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 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.
A node where a link or the whole node is being shutdown SHOULD
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.
4.1.1 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. 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.
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.
4.1.2 Graceful Shutdown of Component Link(s) in a Bundled TE Link
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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.
4.1.3 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.
4.1.4 Graceful Shutdown of Label Resource
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 label resource results in a
significant change event, a new LSA is originated with the new
traffic parameters.
4.2 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 PathErr and
where available, Notify message, in order to achieve this
requirement. These mechanisms apply to both existing and new
LSPs.
4.2.1 Graceful Shutdown of TE link(s)
The node where graceful shutdown of a link or a set of links is
desired MUST trigger a PathErr message with the error code
"Notify" and an error value of "Local link maintenance required"
for all affected LSPs. The "Notify" error code is defined in
[RFC3209] while the "local link maintenance required" error value
is defined in [RFC4736]. The PathErr message SHOULD include the
ERROR_SPEC object containing IP address of the TE Link being
gracefully shutdown. If TE link is unnumbered, the PathErr
message SHOULD include the ERROR_SPEC object containing
unnumbered ID and TE router ID for the TE Link being gracefully
shutdown. If available, and where notify requests were included
when the LSPs were initially setup, Notify message (as defined in
RFC 3471, RFC 3473) MAY also be used for delivery of this
information to the head-end node, border node or PCE.
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When a graceful shutdown operation is performed along the path of
a protected LSP, based on a local decision, the PLR or branch
node MAY redirect the traffic onto the local detour or protecting
segment. In all cases, the PLR or branch node MUST forward the
PathErr to the head-end node, border node, or PCE.
When a head-end node, border node, or PCE receives a PathErr (or
Notify) message with error value of " Local link maintenance
required", it MAY trigger a make-before-break procedure. When
performing path computation for the new LSP, the head-end node,
border node, or PCE SHOULD avoid using the TE resources
identified by the IP address contained in the PathErr (or Notify
message)
4.2.2 Graceful Shutdown of Component Link(s) in a Bundled TE Link
MPLS TE Link Bundling [RFC4201] requires that an LSP is pinned
down to component link(s). Hence, when a component link is
shutdown, the TE LSPs affected by this action need 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 bundled TE
link may still be able to admit new LSPs.
The node where graceful shutdown of a component link is desired
MUST trigger a PathErr message with the error code "Notify" and
the new error value of "Local component link maintenance
required" for all affected LSPs. The "Notify" error code is
defined in [RFC3209] while the "local component link maintenance
required" error value is introduced by this proposal:
12 (TBA) Local component link maintenance required
Error value for "Local component link maintenance required" is to
be assigned by IANA.
The PathErr message should include in the ERROR_SPEC the TE Link
ID address.
If the last component link is being shutdown, the procedure
outlined in Section 4.2.1 is used.
When a head-end node, border node, or PCE receives an RSVP
PathErr or Notify message with error value "local component link
maintenance required" Flag set, it MAY immediately perform a
make-before-break to avoid traffic loss. The head-end node,
border node, or PCE MAY still use the IP address contained in the
PathErr or Notify message in performing path computation for
rerouting the LSP. This is because, this address is an IP address
of the TE link and the flag is an implicit indication that the TE
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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
previously selected MAY be avoided.
4.2.3 Graceful Shutdown of TE Node
The node that is being gracefully shutdown MUST trigger a PathErr
message with the error code "Notify" and an error value of "Local
node maintenance required" for all LSPs. The "Notify" error code
is defined in [RFC3209] while the "local node maintenance
required" error value is defined in [RFC4736].
The PathErr message should include in the ERROR_SPEC object the
MPLS-TE Node ID address
4.2.2 Graceful Shutdown of a Label Resource
The node where graceful shutdown of a label resource is desired
MUST trigger a PathErr message with the error code "Notify" and
the new error value of "Local component link maintenance
required" for the affected LSP. The "Notify" error code is
defined in [RFC3209] while the "local component link maintenance
required" error value is introduced by this proposal:
13 (TBA) Local label resource maintenance required
Error value for "Local label resource maintenance required" is to
be assigned by IANA.
The PathErr message should include in the ERROR_SPEC the TE Link
ID address.
If the last component link is being shutdown, the procedure
outlined in Section 4.2.1 is used.
When a head-end node, border node, or PCE receives an RSVP
PathErr or Notify message with error value "local label resource
maintenance required" Flag set, it MAY immediately perform a
make-before-break to avoid traffic loss. The head-end node,
border node, or PCE MAY still use the IP address contained in the
PathErr or Notify message in performing path computation for
rerouting the LSP. This is because, this address is an IP address
of the TE link and the flag is an implicit indication that the TE
link may still have capacity to admit new LSPs.
5. Security Considerations
This document introduces no new security considerations beyond
those already addressed for existing RSVP PathErr or Notify
messages, or advertisement of TE LSA/LSP containing Link TLV. In
this regard, the security considerations specified in [RFC2205],
[RFC3209] and [MPLS-GMPLS-SECURITY] remain relevant.
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6. IANA Considerations
The following assignment is required in the "Notify" subsection
of "Error Codes and Values" section of the "RSVP PARAMETERS"
registry (located at http://www.iana.org/assignments/rsvp-
parameters):
12 (TBA) - "Local component link maintenance required" flag.
13 (TBA) Local label resource maintenance required.
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
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3209] D. Awduche, L. Berger, D. Gan, T. Li, V. Srinivasan,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels",
RFC 3209, December 2001.
[RFC4736] Jean-Philippe Vasseur, et al "Reoptimization of MPLS
Traffic Engineering loosely routed LSP paths", RFC 4736.
8.2 Informative Reference
[RFC2205] Braden, et al, "Resource ReSerVation Protocol (RSVP)
Version 1, Functional Specification", RFC 2205, December 1997.
[RFC4726] Adrian Farrel, Jean-Philippe Vasseur, Arthi Ayyangar,
"A Framework for Inter-Domain MPLS Traffic Engineering", RFC
4726.
[RFC4201] Kompella, K., Rekhter, Y., Berger, L., "Link Bundling
in MPLS Traffic Engineering", RFC 4201.
[RFC4206] Label Switched Paths (LSP) Hierarchy with Generalized
Multi-Protocol Label Switching (GMPLS) Traffic Engineering (TE),
RFC 4206.
[MPLS-GMPLS-SECURITY] Fang, et al, "Security Framework for MPLS
and GMPLS Networks", draft-fang-mpls-gmpls-security-framework-
00.txt, work in progress.
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9. 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
Jonathan Newton
Cable and Wireless
jonathan.newton@cw.com
10. 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 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.
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11. Disclaimer of Validity
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, THE
IETF TRUST 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.
12. Copyright Statement
Copyright (C) The IETF Trust (2007).
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.
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