Internet Draft                               Lou Berger (Movaz Networks)
Updates: 3473
Category: Standards Track
Expiration Date: November 2004

                                                                May 2004

              GMPLS Signaling Procedure For Egress Control


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.  Internet-Drafts are working
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   This note clarifies the procedures for the control of the label used
   on a output/downstream interface of the egress node of a Label
   Switched Path (LSP).  Such control is also known as "Egress Control".
   Support for Egress Control is implicit in Generalized Multi-Protocol
   Label Switching (GMPLS) Signaling.  This note does not modify GMPLS
   signaling mechanisms and procedures and should be viewed as an
   informative clarification of GMPLS Signaling - Resource ReserVation
   Protocol-Traffic Engineering (RSVP-TE) Extensions.

Berger                                                          [Page 1]

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Author's Note

   This draft is targeted for publication as a BCP.

1. Background

   The ability to control the label used on the output/downstream
   interface of an egress node was one of the early requirements for
   GMPLS.  In the initial GMPLS drafts, this was called "Egress
   Control".  As the GMPLS drafts progressed, the ability to control a
   label on an egress interface was generalized to support control of a
   label on any interface.  This generalization is seen in Section 6 of
   [RFC3471] and Section 5.1 of [RFC3473].  In generalizing this
   functionality, the procedures to support control of a label at the
   egress were also generalized.  While the result was intended to cover
   egress control, this intention is not clear to all.  This note
   reiterates the procedures to cover control of a label used on an
   egress output/downstream interface.

   For context, the following is the text from the GMPLS signaling draft
   dated June 2000:

      6. Egress Control

      The LSR at the head-end of an LSP can control the termination of the
      LSP by using the ERO.  To terminate an LSP on a particular outgoing
      interface of the egress LSR, the head-end may specify the IP address
      of that interface as the last element in the ERO, provided that that
      interface has an associated IP address.

      There are cases where the use of IP address doesn't provide enough
      information to uniquely identify the egress termination.  One case is
      when the outgoing interface on the egress LSR is a component link of
      a link bundle.  Another case is when it is desirable to "splice" two
      LSPs together, i.e., where the tail of the first LSP would be
      "spliced" into the head of the second LSP.  This last case is more
      likely to be used in the non-PSC classes of links.


      6.2. Procedures

      The Egress Label subobject may appear only as the last subobject in
      the ERO/ER.  Appearance of this subobject anywhere else in the ERO/ER
      is treated as a "Bad strict node" error.

      During an LSP setup, when a node processing the ERO/RR performs Next

Berger                                                          [Page 2]

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      Hop selection finds that the second subobject is an Egress Label
      Subobject, the node uses the information carried in this subobject to
      determine the handling of the data received over that LSP.
      Specifically, if the Link ID field of the subobject is non zero, then
      this field identifies a specific (outgoing) link of the node that
      should be used for sending all the data received over the LSP.  If
      the Label field of the subobject is not Implicit NULL label, this
      field specifies the label that should be used as an outgoing label on
      the data received over the LSP.

      Procedures by which an LSR at the head-end of an LSP obtains the
      information needed to construct the Egress Label subobject are
      outside the scope of this document.

2. Egress Control Procedures

   This section is intended to complement Section 5.1.1 and 5.2.1 of
   [RFC3473].  The procedures described in those sections are not
   modified.  This section clarifies procedures related to the label
   used on an egress output/downstream interface.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.1. ERO Procedures

   Egress Control occurs when the node processing an ERO is the egress
   and the ERO contains one or more subobjects related to the
   output/downstream interface.  In this case, the outgoing/downstream
   interface is indicated in the ERO as the last listed local interface.
   Note that an interface may be numbered or unnumbered.

   To support Egress Control, an egress checks to see if the received
   ERO contains an outgoing/downstream interface.  If it does, the type
   of the subobject or subobjects following the interface are examined.
   If the associated LSP is unidirectional, one subobject is examined.
   Two subobjects are examined for bidirectional LSPs.  If the U-bit of
   the subobject being examined is clear (0), then the value of the
   label MUST be used for transmitting traffic associated with the LSP
   on the indicated outgoing/downstream interface.

   If the U-bit of the subobject being examined is set (1), then the
   value of the label is used for upstream traffic associated with the
   bidirectional LSP.  Specifically, the label value will be used for

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   the traffic associated with the LSP that will be received on the
   indicated outgoing/downstream interface.

   Per [RFC3473], any errors encountered while processing the ERO,
   including if the listed label(s) are not acceptable or cannot be
   supported in forwarding, SHOULD result in the generation of a PathErr
   message with the error code "Routing Error" and error value of "Bad
   Explicit Route Object" toward the sender.

2.2. RRO Procedures

   In the case where an ERO is used to specify outgoing interface
   information at the egress and label recording is indicated for the
   LSP, the egress should include the specified interface information
   and the specified label or labels in the corresponding RRO.

3. Security Considerations

   This note clarifies procedures defined in [RFC3473], but does not
   define any new procedures.  As such, no new security considerations
   are introduced.

4. IANA Considerations


5. Acknowledgments

   Valuable comments and input were received from Adrian Farrel, Alan
   Kullberg, and Dimitri Papadimitriou.

Berger                                                          [Page 4]

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6. References

6.1. Normative References

   [BCP78]     Bradner, S., "IETF Rights in Contributions", RFC 3667,
               February 2004.

   [BCP79]     Bradner, S., "Intellectual Property Rights in IETF
               Technology", RFC 3668, February 2004.

   [RFC3471]   Berger, L., Editor, "Generalized Multi-Protocol
               Label Switching (GMPLS) Signaling Functional
               Description", RFC 3471, January 2003.

   [RFC3473]   Berger, L., Editor "Generalized Multi-Protocol Label
               Switching (GMPLS) Signaling - Resource ReserVation
               Protocol-Traffic Engineering (RSVP-TE) Extensions",
               RFC 3473, January 2003.

6.2. Informative References

   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels," RFC 2119.

7. Contact Address

   Lou Berger
   Movaz Networks, Inc.
   7926 Jones Branch Drive
   Suite 615
   McLean VA, 22102
   Phone:  +1 703 847-1801

Berger                                                          [Page 5]

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Berger                                                          [Page 6]

Generated on: Mon May 10 19:23:07 2004