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RFC4003-GMPLS Signaling Procedure for Egress Control

王朝other·作者佚名  2008-05-31
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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).

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.

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.

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.

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: lberger@movaz.com

Full Copyright Statement

Copyright (C) The Internet Society (2005).

This document is subject to the rights, licenses and restrictions

contained in BCP 78, and except as set forth therein, the authors

retain all their rights.

This document and the information contained herein are provided on an

"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS

OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET

ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,

INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE

INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED

WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

The IETF takes no position regarding the validity or scope of any

Intellectual Property Rights or other rights that might be claimed to

pertain to the implementation or use of the technology described in

this document or the extent to which any license under such rights

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made any independent effort to identify any such rights. Information

on the IETF's procedures with respect to rights in IETF Documents can

be found in BCP 78 and BCP 79.

Copies of IPR disclosures made to the IETF Secretariat and any

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Acknowledgement

Funding for the RFC Editor function is currently provided by the

Internet Society.

 
 
 
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