Networking Working Group JP. Vasseur, Ed.
Internet-Draft George. Swallow
Intended status: Best Current Cisco Systems, Inc
Practice Adrian. Farrel
Expires: August 11, 2008 Old Dog Consulting
Ina. Minei
Juniper Networks
February 8, 2008
Node behavior upon originating and receiving Resource ReserVation
Protocol (RSVP) Path Error message
draft-ietf-mpls-3209-patherr-01.txt
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
The aim of this document is to describe a common practice with regard
to the behavior of a node sending a Resource ReserVation Protocol
(RSVP) Traffic Engineering (TE) Path Error message and to the
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behavior of a node receiving an RSVP Path Error message for a
preempted Multi-Protocol Label Switching (MPLS) Traffic Engineering
Label Switched Path (TE LSP). This document does not define any new
protocol extensions.
Requirements Language
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. Protocol behavior . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Behavior at Detecting Nodes . . . . . . . . . . . . . . . . 4
1.2. Behavior at Receiving Nodes . . . . . . . . . . . . . . . . 4
1.3. Data Plane Behavior . . . . . . . . . . . . . . . . . . . . 5
2. RSVP PathErr Messages For a Preempted TE LSP . . . . . . . . . 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
5. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 8
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1. Protocol behavior
[RFC2205] defines two RSVP error message types: PathErr and ResvErr
that are generated when an error occurs. Path Error Messages
(PathErr) are used to report errors and travel upstream toward the
head-end of the flow. Resv Error messages (ResvErr) travel
downstream toward the tail-end of the flow.
This document describes only PathErr message processing for the
specific case of a preempted Traffic Engineering Label Switched Path
(TE LSP) where the term preemption is defined in [RFC3209]. PathErr
messages are routed hop-by-hop using the path state established when
a Path message is routed through the network from the head-end to its
tail-end.
As stated in [RFC2205], PathErr messages do not modify the state of
any node through which they pass; they are only reported to the head-
end of the TE LSP (Traffic Engineering Label Switched Path).
The format of the PathErr message as defined in [RFC2205] is as
follows:
<PathErr message> ::= <Common Header> [ <INTEGRITY> ]
<SESSION> <ERROR_SPEC>
[ <POLICY_DATA> ...]
[ <sender descriptor> ]
<sender descriptor> ::= <SENDER_TEMPLATE> <SENDER_TSPEC>
[ <ADSPEC> ]
The ERROR_SPEC object includes the IP address of the node that
detected the error (Error Node Address), and specifies the error
through two fields. The Error Code field encodes the category of the
error, for example, Policy Control Failure or Unknown object class.
The Error Value field qualifies the error code to indicate the error
with more precision. [RFC3209] extends RSVP as defined in [RFC2205]
for the management of Multi-Protocol Label Switching (MPLS) Traffic
Engineered Label Switched Paths (TE-LSPs). [RFC3209] specifies
several additional conditions that trigger the sending of a RSVP
PathErr message for which new error codes and error values have been
defined that extend the list defined in [RFC2205]. The exact
circumstances under which a TE LSP is preempted and such PathErr
messages are sent are defined in [RFC3209] and will not be repeated
here.
Values for the Error Code and Error Value fields defined in
[RFC2205], [RFC3209], and other documents are maintained in a
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registry by the IANA.
The error conditions fall into two categories:
o Fatal errors represent disruptive conditions for a TE LSP,
o Non-fatal errors are non-disruptive conditions which have occurred
for this TE LSP
Additionally, PathErr messages may be used in two circumstances:
o During TE LSP establishment,
o After a TE LSP has been successfully established.
Nodal behavior is dependent on which combination of the four cases
listed above applies. The following sections describe the expected
behavior at nodes that perform a preemption action for a TE LSP (and
therefore report using error PathErr messages), and at nodes that
receive PathErr messages. This text is a clarification and re-
statement of the procedures set out in [RFC3209] and does not define
any new behavior.
1.1. Behavior at Detecting Nodes
In the case of fatal errors, the detecting node must send a PathErr
message reporting the error condition, and must clear the
corresponding Path and Resv (control plane) states. A direct
implication is that the data plane resources of such a TE LSP are
also released, thus resulting in traffic disruption. It should be
noted, however, that in fatal error cases, the LSP has usually
already failed in the data plane, and traffic has already been
disrupted. When the error arises during LSP establishment, the
implications are different to when it arises on an active LSP since
no traffic flows until the LSP has been fully established. In the
case of non-fatal errors, the detecting node should send a PathErr
message, and must not clear control plane or data plane state.
1.2. Behavior at Receiving Nodes
Nodes that receive PathErr messages are all of the nodes along the
path of the TE LSP upstream of the node that detected the error.
This includes the head-end node. In accordance with [RFC2205] a node
receiving a PathErr message takes no action upon it and consequently
it must not clear Path or Resv control plane or data plane state.
This is true regardless of whether the error condition reported by
the PathErr is fatal or non-fatal. RSVP states should only be
affected upon receiving a PathTear or ResvTear message, or in the
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event of a Path or Resv state timeout. Further discussion of the
processing of these events is outside the scope of this document.
Note that [RFC3473] defines a Path_State_Removed flag in the
ERROR_SPEC object carried on a PathErr message. This field may be
set to change the behavior of upstream nodes that receive the PathErr
message. When set, the flag indicates that the message sender has
removed Path state (and any associated Resv and data plane state) for
the TE LSP. The message receiver should do likewise before
forwarding the message, but may retain state and clear the flag
before forwarding the message.
1.3. Data Plane Behavior
Any node clearing either or both the Path or the Resv state of a TE
LSP MUST also free up the data plane resources allocated to the
corresponding TE LSP.
2. RSVP PathErr Messages For a Preempted TE LSP
Two Error-code can be used to report a preempted TE LSPs:
o As defined in [RFC2750]:Error Code=2: "Policy Control Failure",
Error Value=5 "Flow was preempted"
o As defined in [RFC2205], Error Code=12: "Service preempted"
In both cases, these are fatal errors.
3. Security Considerations
This document does not define any new procedures, but clarifies those
defined in other documents where security considerations are already
specified. This document does not raise specific security issues
beyond those of existing MPLS-TE. By clarifying the procedures, this
document reduces the security risk introduced by non-conformant
implementations.
4. Acknowledgements
The author would like to thank Carol Iturralde, Ashok Narayanan, Rom
Reuther and Reshad Rahman.
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5. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[RFC2750] Herzog, S., "RSVP Extensions for Policy Control",
RFC 2750, January 2000.
[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., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
Authors' Addresses
JP Vasseur (editor)
Cisco Systems, Inc
1414 Massachusetts Avenue
Boxborough, MA 01719
USA
Email: jpv@cisco.com
George Swallow
Cisco Systems, Inc
1414 Massachusetts Avenue
Boxborough, MA 01719
USA
Email: swallow@cisco.com
Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk
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Ina Minei
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, 94089
Email: ina@juniper.net
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