Browse Prior Art Database

MPLS Loop Prevention Mechanism (RFC3063)

IP.com Disclosure Number: IPCOM000005257D
Original Publication Date: 2001-Feb-01
Included in the Prior Art Database: 2001-Aug-20
Document File: 45 page(s) / 94K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

Y. Ohba: AUTHOR [+4]

Abstract

This paper presents a simple mechanism, based on "threads", which can be used to prevent Multiprotocol Label Switching (MPLS) from setting up label switched path (LSPs) which have loops. The mechanism is compatible with, but does not require, VC merge. The mechanism can be used with either the ordered downstream-on-demand allocation or ordered downstream allocation. The amount of information that must be passed in a protocol message is tightly bounded (i.e., no path- vector is used). When a node needs to change its next hop, a distributed procedure is executed, but only nodes which are downstream of the change are involved.

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Network Working Group Y. Ohba Request for Comments: 3063 Y. Katsube Category: Experimental Toshiba

E. Rosen Cisco Systems

P. Doolan Ennovate Networks

February 2001

MPLS Loop Prevention Mechanism

Status of this Memo

This memo defines an Experimental Protocol for the Internet community. It does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2001). All Rights Reserved.

Abstract

This paper presents a simple mechanism, based on "threads", which can be used to prevent Multiprotocol Label Switching (MPLS) from setting up label switched path (LSPs) which have loops. The mechanism is compatible with, but does not require, VC merge. The mechanism can be used with either the ordered downstream-on-demand allocation or ordered downstream allocation. The amount of information that must be passed in a protocol message is tightly bounded (i.e., no path- vector is used). When a node needs to change its next hop, a distributed procedure is executed, but only nodes which are downstream of the change are involved.

Ohba, et al. Experimental [Page 1]

RFC 3063 MPLS Loop Prevention Mechanism February 2001

Table of Contents

1 Introduction .......................................... 2 2 Basic definitions ..................................... 3 3 Thread basics ......................................... 5 3.1 Thread attributes ..................................... 5 3.2 Thread loop ........................................... 7 3.3 Primitive thread actions .............................. 7 3.4 Examples of primitive thread actions ................. 10 4 Thread algorithm ...................................... 14 5 Applicability of the algorithm ........................ 14 5.1 LSP Loop prevention/detection ......................... 15 5.2 Using old path while looping on new path .............. 15 5.3 How to deal with ordered downstream allocation ........ 15 5.4 How to realize load splitting ......................... 15 6 Why this works ........................................ 16 6.1 Why a thread with unknown hop count is extended ....... 16 6.2 Why a rewound thread cannot contain a loop ............ 17 6.2.1 Case1: LSP with known link hop counts ................. 17 6.2.1 Case2: LSP with unknown link hop counts ............... 17 6.3 Why L3 loop is detected ............................... 17 6.4 Why L3 loop is not mis-detected ....................... 17 6.5 How a stalled thread automatically recovers from loop . 18 6.6 Why different colored threads do not chase each other . 18 7 Loop prevention examples .............................. 19 7.1 First example ......................................... 19 7.2 Second example ........................................ 23 8 Thread control block .................................. 24 8.1 Finite state machine .................................. 25 9 Comparison with path-vector/diffusion method .......... 28 10 S...