draft-ietf-mpls-loop-prevention-00.txt		draft-ietf-mpls-loop-prevention-01.txt
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	Eric Rosen		Eric Rosen
	Cisco Systems		Cisco Systems
	Paul Doolan		Paul Doolan
	Ennovate Networks		Ennovate Networks
	May 1999		May 1999
	MPLS Loop Prevention Mechanism		MPLS Loop Prevention Mechanism
	<draft-ietf-mpls-loop-prevention-00.txt>		<draft-ietf-mpls-loop-prevention-01.txt>
	Status of this Memo		Status of this Memo
	This document is an Internet-Draft and is in full conformance with		This document is an Internet-Draft and is in full conformance with
	all provisions of Section 10 of RFC2026.		all provisions of Section 10 of RFC2026.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF), its areas, and its working groups. Note that		Task Force (IETF), its areas, and its working groups. Note that
	other groups may also distribute working documents as Internet-		other groups may also distribute working documents as Internet-
	Drafts.		Drafts.
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	months and may be updated, replaced, or obsoleted by other documents		months and may be updated, replaced, or obsoleted by other documents
	at any time. It is inappropriate to use Internet-Drafts as		at any time. It is inappropriate to use Internet-Drafts as
	reference material or to cite them other than as "work in progress."		reference material or to cite them other than as "work in progress."
	The list of current Internet-Drafts can be accessed at		The list of current Internet-Drafts can be accessed at
	http://www.ietf.org/ietf/1id-abstracts.txt		http://www.ietf.org/ietf/1id-abstracts.txt
	The list of Internet-Draft Shadow Directories can be accessed at		The list of Internet-Draft Shadow Directories can be accessed at
	http://www.ietf.org/shadow.html.		http://www.ietf.org/shadow.html.
			To view the list Internet-Draft Shadow Directories, see
			http://www.ietf.org/shadow.html.
	Abstract		Abstract
	This paper presents a simple mechanism, based on "threads", which		This paper presents a simple mechanism, based on "threads", which
	can be used to prevent MPLS from setting up label switched path		can be used to prevent MPLS from setting up label switched path
	(LSPs) which have loops. The mechanism is compatible with, but does		(LSPs) which have loops. The mechanism is compatible with, but does
	not require, VC merge. The mechanism can be used with either the		not require, VC merge. The mechanism can be used with either the
	ordered downstream-on-demand allocation or ordered downstream		ordered downstream-on-demand allocation or ordered downstream
	allocation. The amount of information that must be passed in a		allocation. The amount of information that must be passed in a
	protocol message is tightly bounded (i.e., no path-vector is used).		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		When a node needs to change its next hop, a distributed procedure is
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	maintained by the node. The path setup messages that the node sends		maintained by the node. The path setup messages that the node sends
	downstream will contain this color. Also, when the node sends such		downstream will contain this color. Also, when the node sends such
	a message downstream, it will remember the color, and this color		a message downstream, it will remember the color, and this color
	becomes the color of the downstream link.		becomes the color of the downstream link.
	When a colored message is received, its color becomes the color of		When a colored message is received, its color becomes the color of
	the incoming link. The thread which consists of messages of a		the incoming link. The thread which consists of messages of a
	certain color will be known as a thread of that color.		certain color will be known as a thread of that color.
	A special color value "transparent"(=all 0's) is reserved.		A special color value "transparent"(=all 0's) is reserved.
			One possible method for unique color assignment is, starting the
			event identifier from its initial value, and incrementing it by one
			(modulo its maximum value) each time a color is assigned. In this
			method, the initial event identifier is either selected at random or
			assigned to be larger than the largest event identifier used on the
			previous system incarnation.
	Thread Hop Count		Thread Hop Count
	In order to maintain link hop counts, we need to carry hop counts in		In order to maintain link hop counts, we need to carry hop counts in
	the path control messages. For instance, a leaf node would assign a		the path control messages. For instance, a leaf node would assign a
	hop count of 1 to its downstream link, and would store that value		hop count of 1 to its downstream link, and would store that value
	into a path setup message it sends downstream. When a path setup		into a path setup message it sends downstream. When a path setup
	message is sent downstream, a node would assign a hop count which is		message is sent downstream, a node would assign a hop count which is
	one more than the largest of the incoming link hop counts, to its		one more than the largest of the incoming link hop counts, to its
	downstream link, and would store that value into a path setup		downstream link, and would store that value into a path setup
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