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 (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.
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
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.
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