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

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
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Copyright Notice

   Copyright (C) The IETF Trust (2008).


   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",
   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

   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

   <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

   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

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


   George Swallow
   Cisco Systems, Inc
   1414 Massachusetts Avenue
   Boxborough, MA  01719


   Adrian Farrel
   Old Dog Consulting


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   Ina Minei
   Juniper Networks
   1194 North Mathilda Ave.
   Sunnyvale,   94089


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