    Network Working Group                                          L. Berger
    Request for Comments: 4003                                Movaz Networks
    Updates: 3473                                              February 2005
    Category: Standards Track

                  GMPLS Signaling Procedure for Egress Control

    Status of This Memo

       This document specifies an Internet standards track protocol for the
       Internet community, and requests discussion and suggestions for
       improvements.  Please refer to the current edition of the "Internet
       Official Protocol Standards" (STD 1) for the standardization state
       and status of this protocol.  Distribution of this memo is unlimited.

    Copyright Notice

       Copyright (C) The Internet Society (2005).

    Abstract

       This document clarifies the procedures for the control of the label
       used on an output/downstream interface of the egress node of a Label
       Switched Path (LSP).  This control is also known as "Egress Control".
       Support for Egress Control is implicit in Generalized Multi-Protocol
       Label Switching (GMPLS) Signaling.  This document clarifies the
       specification of GMPLS Signaling and does not modify GMPLS signaling
       mechanisms and procedures.

    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 documents, this was called "Egress
       Control".  As the GMPLS documents 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].  When this functionality
       was generalized, the procedures to support control of a label at the
       egress were also generalized.  Although 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.

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    RFC 4003      GMPLS Signaling Procedure for Egress Control February 2005

       For context, the following is the text from the GMPLS signalling
       document dated June 2000 about how ERO (Explicit Route Object) for
       egress control:

          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 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 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 Sections 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.

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    RFC 4003      GMPLS Signaling Procedure for Egress Control February 2005

       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].

    2.1.  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 whether the
       received ERO contains an outgoing/downstream interface.  If it does,
       the type of the subobject or subobjects following the interface is
       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
       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".

    2.2.  RRO Procedures

       If 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 (Route Record Object).

    3.  Security Considerations

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

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    RFC 4003      GMPLS Signaling Procedure for Egress Control February 2005

    4.  Acknowledgments

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

    5.  Normative References

       [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.

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

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

    Author's Address

       Lou Berger
       Movaz Networks, Inc.
       7926 Jones Branch Drive
       Suite 615
       McLean VA, 22102

       Phone:  +1 703 847-1801
       EMail:  lberger@movaz.com

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    RFC 4003      GMPLS Signaling Procedure for Egress Control February 2005

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    Acknowledgement

       Funding for the RFC Editor function is currently provided by the
       Internet Society.

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