





Internet Engineering Task Force (IETF)                  JP. Vasseur, Ed.
Request for Comments: 5711                                    G. Swallow
Updates: 3209                                        Cisco Systems, Inc.
Category: Standards Track                                       I. Minei
ISSN: 2070-1721                                         Juniper Networks
                                                            January 2010


   Node Behavior upon Originating and Receiving Resource Reservation
                  Protocol (RSVP) Path Error Messages

Abstract

   The aim of this document is to describe a common practice with regard
   to the behavior of nodes that send and receive a Resource Reservation
   Protocol (RSVP) Traffic Engineering (TE) Path Error messages for a
   preempted Multiprotocol Label Switching (MPLS) or Generalized MPLS
   (GMPLS) Traffic Engineering Label Switched Path (TE LSP).  (For
   reference to the notion of TE LSP preemption, see RFC 3209.)  This
   document does not define any new protocol extensions.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5711.

















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Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................3
      1.1. Requirements Language ......................................3
   2. Protocol Behavior ...............................................3
      2.1. Behavior at Detecting Nodes ................................4
      2.2. Behavior at Receiving Nodes ................................5
      2.3. Data-Plane Behavior ........................................5
   3. RSVP PathErr Messages for a Preempted TE LSP ....................5
   4. Security Considerations .........................................5
   5. Acknowledgements ................................................6
   6. References ......................................................6
      6.1. Normative References .......................................6
      6.2. Informative References .....................................6






















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1.  Introduction

   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
   behavior of a node receiving an RSVP Path Error message for a
   preempted Multiprotocol Label Switching (MPLS) and Generalized MPLS
   (GMPLS) Traffic Engineering Label Switched Path (TE LSP).  (For
   reference to the notion of TE LSP preemption, see [RFC3209]).

   [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 TE LSP, where the term preemption is
   defined in [RFC3209].

1.1.  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].

2.  Protocol Behavior

   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 is defined in Section 3. of
   [RFC2205].

   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 MPLS-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



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   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
   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 that have occurred
      for this TE LSP.

   PathErr messages may be used in two circumstances:

   o  during TE LSP establishment, and

   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
   restatement of the procedures set out in [RFC3209] and does not
   define any new behavior.

2.1.  Behavior at Detecting Nodes

   In the case of fatal errors ("Hard Preemption"; see Section 4.7.3 of
   [RFC3209] ), 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.







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2.2.  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 Section 3.7.1 of
   [RFC2205], a node receiving a PathErr message takes no action upon
   it, and consequently the node 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 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.

2.3.  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.

3.  RSVP PathErr Messages for a Preempted TE LSP

   Two Error Codes have been defined to report a preempted TE LSP:

   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"

   They are both fatal errors.

4.  Security Considerations

   This document does not define any new procedures, but clarifies those
   defined in other documents where security considerations are already
   specified in [RFC3209] and [RFC3473].  This document does not raise
   specific security issues beyond those of existing MPLS-TE.  By





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   clarifying the procedures, this document reduces the security risk
   introduced by non-conformant implementations.  See [SEC_FMWK] for
   further discussion of MPLS security issues.

5.  Acknowledgements

   The authors would like to thank Carol Iturralde, Ashok Narayanan, Rom
   Reuther, and Reshad Rahman.

6.  References

6.1.  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.

6.2.  Informative References

   [SEC_FMWK]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
               Networks", Work in Progress, October 2009.















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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


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

   EMail: ina@juniper.net
























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