Networking Working Group
Internet Draft
Zafar Ali
Jean-Philippe Vasseur
Anca Zamfir
Cisco Systems, Inc.
IETF Internet Draft
Category: Informational
Expires: September 2007 March 2007
draft-ietf-ccamp-mpls-graceful-shutdown-02.txt
Graceful Shutdown in GMPLS Traffic Engineering Networks
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Copyright (C) The IETF Trust (2007).
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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
In examples, "C:" and "S:" indicate lines sent by the client and
server respectively.
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 0.
Table of Contents
1. Terminology.....................................................2
2. Introduction....................................................3
3. Requirements for Graceful Shutdown..............................4
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................................6
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................................7
5. Security Considerations.........................................7
6. IANA Considerations.............................................7
7. Acknowledgments.................................................7
8. Reference.......................................................7
8.1 Normative Reference...........................................7
8.2 Informative Reference.........................................7
Author's Addresses.................................................8
Intellectual Property Statement....................................8
Disclaimer of Validity.............................................9
1. Terminology
LSR - Label Switching Device.
LSP - An MPLS Label Switched Path
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Head-end or Ingress node: In this document the terms head-end
node equally applies to the Ingress node that initiated signaling
for the 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
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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
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
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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.
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
RFC 3471, RFC 3473) MAY also be used for delivery of this
information to the head-end nodes. When a GS operation is
performed along the path of a protected LSP, the PLR or branch
node SHOULD NOT redirect the traffic onto the local detour or
protecting segment. This is to make rerouting process local to
the headend node, without intervention of the recovery process.
Please recall that head-end node terminology in this document
equally applies to the Ingress node that initiated signaling for
the Path, or an intermediate node (in the case of loose hops path
computation). If the resource being gracefully shutdown is on the
Path of the protecting LSP/ local detour, the branch node/ PLR
reroutes the protecting LSP/ local detour just a head-end LSR
would reroute any other LSP.
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 the RSVP error-code "Routing Problem" (24) [RSVP-TE] is
needed:
9 (TBA) Local component link maintenance required
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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 avoided.
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.
4.2
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
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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 "Local component link maintenance required" flag.
7.
Acknowledgments
The authors would like to acknowledge useful comments from David
Ward, Sami Boutros, Adrian Farrel and Dimitri Papadimitriou.
8.
Reference
8.1
Normative Reference
[RSVP-TE] 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.
[PATH-REOPT] Jean-Philippe Vasseur, et al "Reoptimization of MPLS
Traffic Engineering loosely routed LSP paths", RFC 4736.
8.2
Informative Reference
[RSVP] Braden, et al, "Resource ReSerVation Protocol (RSVP) -
Version 1, Functional Specification", RFC 2205, September 1997.
[INTER-AREA-AS] Adrian Farrel, Jean-Philippe Vasseur, Arthi
Ayyangar, "A Framework for Inter-Domain MPLS Traffic
Engineering", 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)
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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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