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:  [email protected]























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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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