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Versions: (draft-berger-mpls-gmpls-lsp-reroute)
00 01 02 03 04 05 06 RFC 5710
Internet Draft Lou Berger (LabN)
Category: Best Common Practice
Expiration Date: February 5, 2009 Dimitri Papadimitriou (Alcatel Lucent)
JP. Vasseur (Cisco)
August 5, 2008
PathErr Message Triggered MPLS and GMPLS LSP Reroute
draft-ietf-mpls-gmpls-lsp-reroute-00.txt
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
This document describes how Resource ReserVation Protocol (RSVP)
PathErr Messages may be used to trigger rerouting of Multi-Protocol
Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic
Engineering (TE) Label Switched Paths (LSPs) without first removing
LSP state or resources. Such LSP rerouting may be desirable in a
number of cases including, for example, soft-preemption and graceful
shutdown. This document describes the usage of existing Standards
Track mechanisms and defines no new formats or mechanisms. It relies
on mechanisms already defined as part of RSVP-TE and simply describes
a sequence of actions to be executed.
Berger, et al Best Common Practice [Page 1]
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Table of Contents
1 Introduction .............................................. 3
1.1 Conventions used in this document ......................... 4
2 Reroute Requests .......................................... 4
2.1 Processing at Requesting Node ............................. 4
2.1.1 Reroute Request Timeouts .................................. 5
2.2 Processing at Upstream Node ............................... 5
2.3 Processing at Ingress ..................................... 6
3 IANA Considerations ....................................... 6
4 Security Considerations ................................... 6
5 References ................................................ 6
5.1 Normative References ...................................... 6
5.2 Informative References .................................... 7
6 Acknowledgments ........................................... 7
7 Author's Addresses ........................................ 8
8 Full Copyright Statement .................................. 8
9 Intellectual Property ..................................... 8
Berger, et al Best Common Practice [Page 2]
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1. Introduction
Resource ReserVation Protocol (RSVP), see [RFC2205], has been
extended to support the control of Traffic Engineering (TE) Label
Switched Paths (LSPs) for both Multi-Protocol Label Switching (MPLS)
and Generalized MPLS (GMPLS) in, respectively, [RFC3209] and
[RFC3473]. In all cases, a PathErr message is used to report errors
to nodes upstream of the error detecting node. As defined in
[RFC2205], and left unmodified by [RFC3209], PathErr messages "do not
change path state in the nodes through which they pass".
Notwithstanding this definition, PathErr messages are most commonly
used to report errors during LSP establishment, i.e. the RSVP-TE
processing that occurs prior to the ingress receiving a Resv message.
(See [PATHERR] for a broader discussion on PathErr message handling.)
Support for such usage was enhanced via the introduction of the
Path_State_Removed flag in [RFC3473], which enables a processing node
to free related LSP state and resources. The usage of PathErr
messages during LSP establishment was further covered in [RFC4920]
which describes in detail how a node may indicate that the node or
one of its associated resources should be avoided, i.e., routed
around, during LSP establishment.
PathErr messages can also be used to support a number of other cases
that can occur after an LSP is established. This document focuses on
the cases where PathErr messages can be used for a node to indicate
that it desires an upstream node to reroute an LSP around the
indicating node or a resources associated with the indicating node.
Some examples of such cases are soft-preemption and graceful
shutdown. (See [PREEMPTION] and [GRACEFUL]).
This document uses the terminology "reroute request" to refer to the
indication by a node that an upstream reroute should take place. This
document how a node can initiate a reroute request without disrupting
LSP data traffic or, when so desired, with the disruption of data
traffic and removal of LSP associated state and resources.
The mechanisms used to indicate reroute requests are derived from the
mechanisms described in [RFC4920], and the error codes defined in
[RFC4736]. This document describes (1) how a non-disruptive reroute
request may be issued and, (2) based on an optional "timeout" period,
how rerouting may be forced by removing LSP state and associated
resources and signaling such removal.
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1.1. 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 [RFC2119].
2. Reroute Requests
This section describes how a downstream node can indicate that it
desires a node upstream (along the LSP path) to initiate the re-
routing of an LSP, and how the upstream nodes can respond to such a
request. Initiating nodes, transit nodes, and ingress nodes are
described separately.
2.1. Processing at Requesting Node
When a transit or egress node desires to request the rerouting of an
established LSP, it MUST first determine if it can act on the reroute
request locally. A reroute request may be acted on locally if the
ERO received in the LSP's incoming Path message does not precluded
the reroute and the node's policy allows local repair. Examples of
reroute requests that may be permissible are reroutes avoiding
outgoing interface, component, label resource, or next hops not
explicitly listed in the ERO. When the reroute request can be
processed locally, standard local repair processing MUST be followed.
The node SHOULD limit the number of local repair attempts. The
expected norm is for local repair and, thereby, this case to be
precluded by policy.
When the requesting node cannot act on a reroute request locally, it
MUST issue a PathErr message with the error code "Notify" and a value
of either "Local link maintenance required" or "Local node
maintenance required". The error value is based on the local reroute
request. If the local request directs a reroute around the local
node, the error value "Local node maintenance required" MUST be used
and the local node MUST be indicated in the ERROR_SPEC object.
If the local request does not direct a reroute around the local node,
the error value "Local link maintenance required" MUST be used, and
the impacted interface MUST be indicated in the ERROR_SPEC object.
The IF_ID ERROR_SPEC SHOULD also be used when supported. The TLVs
defined in [RFC4920] MAY also be used when supported and when they
can provide specific additional reroute request information, e.g.,
reroute around a specific label. The principles related to
ERROR_SPEC object construction defined in section 6.3.1. of [RFC4920]
SHOULD be followed.
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2.1.1. Reroute Request Timeouts
Reroute request timeouts are used to remove an LSP when there is no
response to a reroute request. Reroute request timeouts MUST NOT be
used, when the LSP is not to be removed at the expiration of the
Reroute request timeout period. When such LSP removal is desired and
after initiating a reroute request, the initiating node MUST initiate
a timeout during which it expects to receive a response to the
reroute request. Valid responses are a PathTear message or a trigger
Path message with an ERO avoiding the resource that was indicated in
the reroute request. If either type of message is received, the
timeout period MUST be canceled and no further action is needed.
Note, normal refresh processing is not modified by the introduction
of reroute request timeouts. Such processing may result in Path
state being removed during the timeout period, in which case the
timeout period MUST also be canceled.
If the reroute request timeout is reached, the initiating node MUST
remove the LSP and its associated state and resources. Removal of
LSP state is indicated downstream via a corresponding PathTear
message. Removal is indicated upstream via a PathErr message with
the error code of "Service preempted". The Path_State_Removed flag
MUST be set if supported. When the Path_State_Removed flag is not
supported, a corresponding ResvTear MUST also be sent.
2.2. Processing at Upstream Node
When a transit node's policy permits it to support reroute request
processing and local repair, the node MUST examine incoming PathErr
messages to see it the node can perform a requested reroute. A
reroute request is indicated by the error code and value of
"Notify/Local (link or node) maintenance required" in a received
PathErr message. A transit node MAY act on a reroute request locally
when the ERO received in the LSP's incoming Path message does not
precluded the reroute. As before, examples include loosely routed
LSP next hops. When the reroute request can be processed locally,
standard local repair processing MUST be followed. The node SHOULD
limit the number of local repair attempts. Again, the expected norm
is for local repair and, thereby, this case to be precluded due to
policy.
When the transit node supports [RFC4920], is a boundary node and
Boundary Re-routing is allowed, it SHOULD use a route request as a
trigger to reroute the LSP. (Per [RFC4920], the Flags field of the
LSP_ATTRIBUTES object of the initial Path message indicate "Boundary
re-routing".) In the case the node triggers rerouting, it first MUST
identify an alternate path within the domain. When such a path is
Berger, et al Best Common Practice [Page 5]
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available, the node MUST terminate the PathErr message and issue a
Path message reflecting the identified alternate path. Processing
then continues per [RFC4920]. When an alternate path is note
available, the node cannot act on the reroute request.
When a transit node node cannot act on a reroute request locally, per
standard processing, it MUST propagate the received PathErr message
to the previous hop.
2.3. Processing at Ingress
When reroute processing is supported, an ingress node MUST check
received PathErr messages to identify them as indicating reroute
requests. A reroute request is indicated by the error code and value
of "Notify/Local (link or node) maintenance required" in a received
PathErr message. Upon receiving a reroute request, the ingress MUST
attempt to identify an alternate path, avoiding the node, interface,
resource, etc. identified within the ERROR_SPEC object. When an
alternate path cannot be identified the reroute request MUST be
discarded. When an alternate path is identified, a corresponding
make-before-break LSP SHOULD be initiated, and standard make-before-
break procedures MUST be followed.
3. IANA Considerations
No new IANA administered values are requested by this document.
4. Security Considerations
This document introduces no new security considerations as this
document describes usage of existing formats and mechanisms. The
Section 9 of [RFC4920] and [RFC4736] should be used as the starting
point for reviewing the security considerations related to the
formats and mechanisms discussed in this document.
5. References
5.1. Normative References
[RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S. and S. Jamin,
"Resource ReSerVation Protocol (RSVP) -- Version 1,
Functional Specification", RFC 2205, September 1997.
Berger, et al Best Common Practice [Page 6]
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels," RFC 2119.
[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.
[RFC3473] Berger, L., Editor, "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling - Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions",
RFC 3473, January 2003.
[RFC4920] Farrel, A., Ed., "Crankback Signaling Extensions for
MPLS and GMPLS RSVP-TE", RFC 4920, July 2007.
5.2. Informative References
[RFC4736] Vasseur, JP., et al, "Reoptimization of Multiprotocol
Label Switching (MPLS) Traffic Engineering (TE) Loosely
Routed Label Switched Path (LSP)", RFC 4736, November
2006.
[GRACEFUL] Ali, Z., et al., "Graceful Shutdown in MPLS and
Generalized MPLS Traffic Engineering Networks",
draft-ietf-ccamp-mpls-graceful-shutdown-05.txt,
Work in Progress, January 2008
[PATHERR] Vasseur, JP., Ed. "Node behavior upon originating and
receiving Resource ReserVation Protocol (RSVP) Path
Error message", draft-ietf-mpls-3209-patherr-02.txt,
Work in Progress, February 2008.
[PREEMPTION] Meyer, M., Ed. "MPLS Traffic Engineering Soft
Preemption", draft-ietf-mpls-soft-preemption-10.txt,
Work in Progress, February 2008.
6. Acknowledgments
This document was conceived along with Matthew Meyer.
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7. Author's Addresses
Lou Berger
LabN Consulting, L.L.C.
Phone: +1-301-468-9228
Email: lberger@labn.net
Dimitri Papadimitriou
Alcatel Lucent
Francis Wellesplein 1,
B-2018 Antwerpen, Belgium
Phone: +32 3 240-8491
Email: Dimitri.Papadimitriou@alcatel-lucent.be
JP Vasseur
Cisco Systems, Inc
1414 Massachusetts Avenue
Boxborough, MA 01719
USA
Email: jpv@cisco.com
8. Full Copyright Statement
Copyright (C) The IETF Trust (2008).
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Berger, et al Best Common Practice [Page 8]
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Acknowledgement
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Berger, et al Best Common Practice [Page 9]
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