Network Working Group                        Lou Berger (Movaz Networks)
Internet Draft
Expiration Date: May 2004

                                                           November 2003


              GMPLS Signaling Procedure For Egress Control


                draft-berger-gmpls-egress-control-00.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
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Abstract

   This note clarifies the procedures for the control of a label used on
   an egress output/downstream interface.  Such control is also know and
   "Egress Control".  Support for Egress Control is implicit in
   Generalized Multi-Protocol Label Switching (GMPLS) Signaling
   [RFC3471] and [RFC3473].  This note does not modify GMPLS signaling
   mechanisms and procedures and should be viewed as an informative
   clarification of [RFC3473].


















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. Background

   The ability to control a label used on an egress output/downstream
   interface 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 resulting 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.

   and

      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



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      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.


. Egress Control Procedures

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


2.1. ERO Procedures

   Egress Control occurs when the node processing an ERO is the egress
   and the ERO contains one or more label subobjects.  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 unicast, 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 is
   copied into a new Label_Set object.  This Label_Set object indicates
   the label value that 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 message
   containing a "Bad EXPLICIT_ROUTE object" error.





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2.2. RRO Procedures

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


. Security Considerations

   This note clarifies procedures defined in [RFC3473].  As such, no new
   security considerations are introduced.


. IANA Considerations

   None.


. References

[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.



. Contact 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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