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).
AbstractThis 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. 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.
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. 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.
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]. 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". RFC3473] but does not define any new procedures. As such, no new security considerations are introduced.
[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.
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