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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).


 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.

Berger Standards Track [Page 1] 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.

Berger Standards Track [Page 2] RFC 4003 GMPLS Signaling Procedure for Egress Control February 2005

 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 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.

Berger Standards Track [Page 3] 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

Berger Standards Track [Page 4] RFC 4003 GMPLS Signaling Procedure for Egress Control February 2005

Full Copyright Statement

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Berger Standards Track [Page 5]

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