draft-ietf-ipv6-2461bis-11.txt		rfc4861.txt
	INTERNET-DRAFT T. Narten,		Network Working Group T. Narten
	Expires: September 2007 IBM		Request for Comments: 4861 IBM
	Obsoletes: 2461 (if approved) E. Nordmark,		Obsoletes: 2461 E. Nordmark
	Sun Microsystems		Category: Standards Track Sun Microsystems
	W. Simpson,		W. Simpson
	Daydreamer		Daydreamer
	H. Soliman,		H. Soliman
	Elevate Technologies		Elevate Technologies
	March, 2007		September 2007
	Neighbor Discovery for IP version 6 (IPv6)		Neighbor Discovery for IP version 6 (IPv6)
	<draft-ietf-ipv6-2461bis-11.txt>
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	Copyright (C) The IETF Trust (2007).		This document specifies an Internet standards track protocol for the
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	Abstract		Abstract
	This document specifies the Neighbor Discovery protocol for IP		This document specifies the Neighbor Discovery protocol for IP
	Version 6. IPv6 nodes on the same link use Neighbor Discovery to		Version 6. IPv6 nodes on the same link use Neighbor Discovery to
	discover each other's presence, to determine each other's link-layer		discover each other's presence, to determine each other's link-layer
	addresses, to find routers and to maintain reachability information		addresses, to find routers, and to maintain reachability information
	about the paths to active neighbors.		about the paths to active neighbors.
	Table of Contents		Table of Contents
	1. INTRODUCTION....................................................3		1. Introduction ....................................................4
	2. TERMINOLOGY.....................................................4		2. Terminology .....................................................4
	2.1. General....................................................4		2.1. General....................................................4
	2.2. Link Types.................................................7		2.2. Link Types .................................................8
	2.3. Addresses..................................................9		2.3. Addresses..................................................9
	2.4. Requirements...............................................9		2.4. Requirements ..............................................10
	3. PROTOCOL OVERVIEW..............................................10		3. Protocol Overview ..............................................10
	3.1. Comparison with IPv4......................................13		3.1. Comparison with IPv4 ......................................14
	3.2. Supported Link Types......................................15		3.2. Supported Link Types ......................................16
	3.3. Securing Neighbor Discovery messages.......................17		3.3. Securing Neighbor Discovery Messages ......................18
	4. MESSAGE FORMATS................................................17		4. Message Formats ................................................18
	4.1. Router Solicitation Message Format........................17		4.1. Router Solicitation Message Format ........................18
	4.2. Router Advertisement Message Format.......................18		4.2. Router Advertisement Message Format .......................19
	4.3. Neighbor Solicitation Message Format......................20		4.3. Neighbor Solicitation Message Format ......................22
	4.4. Neighbor Advertisement Message Format.....................22		4.4. Neighbor Advertisement Message Format .....................23
	4.5. Redirect Message Format...................................24		4.5. Redirect Message Format ...................................26
	4.6. Option Formats............................................26		4.6. Option Formats ............................................28
	4.6.1. Source/Target Link-layer Address.....................26		4.6.1. Source/Target Link-layer Address ...................28
	4.6.2. Prefix Information...................................27		4.6.2. Prefix Information .................................29
	4.6.3. Redirected Header....................................29		4.6.3. Redirected Header ..................................31
	4.6.4. MTU..................................................30		4.6.4. MTU ................................................32
	5. CONCEPTUAL MODEL OF A HOST.....................................31		5. Conceptual Model of a Host .....................................33
	5.1. Conceptual Data Structures................................31		5.1. Conceptual Data Structures ................................33
	5.2. Conceptual Sending Algorithm..............................33		5.2. Conceptual Sending Algorithm ..............................36
	5.3. Garbage Collection and Timeout Requirements...............34		5.3. Garbage Collection and Timeout Requirements ...............37
	6. ROUTER AND PREFIX DISCOVERY....................................35		6. Router and Prefix Discovery ....................................38
	6.1. Message Validation........................................36		6.1. Message Validation ........................................39
	6.1.1. Validation of Router Solicitation Messages...........36		6.1.1. Validation of Router Solicitation Messages .........39
	6.1.2. Validation of Router Advertisement Messages..........36		6.1.2. Validation of Router Advertisement Messages ........39
	6.2. Router Specification......................................37		6.2. Router Specification ......................................40
	6.2.1. Router Configuration Variables.......................37		6.2.1. Router Configuration Variables .....................40
	6.2.2. Becoming An Advertising Interface....................41		6.2.2. Becoming an Advertising Interface ..................45
	6.2.3. Router Advertisement Message Content.................42		6.2.3. Router Advertisement Message Content ...............45
	6.2.4. Sending Unsolicited Router Advertisements............43		6.2.4. Sending Unsolicited Router Advertisements ..........47
	6.2.5. Ceasing To Be An Advertising Interface...............43		6.2.5. Ceasing To Be an Advertising Interface .............47
	6.2.6. Processing Router Solicitations......................44		6.2.6. Processing Router Solicitations ....................48
	6.2.7. Router Advertisement Consistency.....................45		6.2.7. Router Advertisement Consistency ...................50
	6.2.8. Link-local Address Change............................46		6.2.8. Link-local Address Change ..........................50
	6.3. Host Specification........................................47		6.3. Host Specification ........................................51
	6.3.1. Host Configuration Variables.........................47		6.3.1. Host Configuration Variables .......................51
	6.3.2. Host Variables.......................................47		6.3.2. Host Variables .....................................51
	6.3.3. Interface Initialization.............................48		6.3.3. Interface Initialization ...........................52
	6.3.4. Processing Received Router Advertisements............48		6.3.4. Processing Received Router Advertisements ..........53
	6.3.5. Timing out Prefixes and Default Routers..............51		6.3.5. Timing out Prefixes and Default Routers ............56
	6.3.6. Default Router Selection.............................51		6.3.6. Default Router Selection ...........................56
	6.3.7. Sending Router Solicitations.........................52		6.3.7. Sending Router Solicitations .......................57
	7. ADDRESS RESOLUTION AND NEIGHBOR UNREACHABILITY DETECTION.......53		7. Address Resolution and Neighbor Unreachability Detection .......59
	7.1. Message Validation........................................54		7.1. Message Validation ........................................59
	7.1.1. Validation of Neighbor Solicitations.................54		7.1.1. Validation of Neighbor Solicitations ...............59
	7.1.2. Validation of Neighbor Advertisements................55		7.1.2. Validation of Neighbor Advertisements ..............60
	7.2. Address Resolution........................................55		7.2. Address Resolution ........................................60
	7.2.1. Interface Initialization.............................56		7.2.1. Interface Initialization ...........................61
	7.2.2. Sending Neighbor Solicitations.......................56		7.2.2. Sending Neighbor Solicitations .....................61
	7.2.3. Receipt of Neighbor Solicitations....................57		7.2.3. Receipt of Neighbor Solicitations ..................62
	7.2.4. Sending Solicited Neighbor Advertisements............58		7.2.4. Sending Solicited Neighbor Advertisements ..........63
	7.2.5. Receipt of Neighbor Advertisements...................59		7.2.5. Receipt of Neighbor Advertisements .................64
	7.2.6. Sending Unsolicited Neighbor Advertisements..........60		7.2.6. Sending Unsolicited Neighbor Advertisements ........66
	7.2.7. Anycast Neighbor Advertisements......................62		7.2.7. Anycast Neighbor Advertisements ....................67
	7.2.8. Proxy Neighbor Advertisements........................62		7.2.8. Proxy Neighbor Advertisements ......................68
	7.3. Neighbor Unreachability Detection.........................63		7.3. Neighbor Unreachability Detection .........................68
	7.3.1. Reachability Confirmation............................63		7.3.1. Reachability Confirmation ..........................69
	7.3.2. Neighbor Cache Entry States..........................64		7.3.2. Neighbor Cache Entry States ........................70
	7.3.3. Node Behavior........................................65		7.3.3. Node Behavior ......................................71
	8. REDIRECT FUNCTION..............................................67		8. Redirect Function ..............................................73
	8.1. Validation of Redirect Messages...........................67		8.1. Validation of Redirect Messages ...........................74
	8.2. Router Specification......................................68		8.2. Router Specification ......................................75
	8.3. Host Specification........................................69		8.3. Host Specification ........................................76
	9. EXTENSIBILITY - OPTION PROCESSING..............................70		9. Extensibility - Option Processing ..............................76
	10. PROTOCOL CONSTANTS............................................71		10. Protocol Constants ............................................78
	11. SECURITY CONSIDERATIONS.......................................73		11. Security Considerations .......................................79
	11.1 Threat analysis............................................73		11.1. Threat Analysis ..........................................79
	11.2 Securing Neighbor Discovery messages.......................74		11.2. Securing Neighbor Discovery Messages .....................81
	12. RENUMBERING CONSIDERATIONS....................................75		12. Renumbering Considerations ....................................81
	IANA CONSIDERATIONS................................................76		13. IANA Considerations ...........................................83
	REFERENCES.........................................................77		14. References ....................................................84
	Authors' Addresses.................................................79		14.1. Normative References .....................................84
	APPENDIX A: MULTIHOMED HOSTS.......................................80		14.2. Informative References ...................................84
	APPENDIX B: FUTURE EXTENSIONS......................................81		Appendix A: Multihomed Hosts ......................................87
	APPENDIX C: STATE MACHINE FOR THE REACHABILITY STATE...............82		Appendix B: Future Extensions .....................................88
	APPENDIX D: SUMMARY OF ISROUTER RULES..............................84		Appendix C: State Machine for the Reachability State ..............89
	APPENDIX E: IMPLEMENTATION ISSUES..................................85		Appendix D: Summary of IsRouter Rules .............................91
	APPENDIX F: CHANGES FROM RFC 2461..................................86		Appendix E: Implementation Issues .................................92
	Intellectual Property Statement....................................87		Appendix F: Changes from RFC 2461 .................................94
	Full Copyright Statement...........................................88		Acknowledgments ...................................................95
	Disclaimer of Validity.............................................88
	1. INTRODUCTION		1. Introduction
	This specification defines the Neighbor Discovery (ND) protocol for		This specification defines the Neighbor Discovery (ND) protocol for
	Internet Protocol Version 6 (IPv6). Nodes (hosts and routers) use		Internet Protocol Version 6 (IPv6). Nodes (hosts and routers) use
	Neighbor Discovery to determine the link-layer addresses for		Neighbor Discovery to determine the link-layer addresses for
	neighbors known to reside on attached links and to quickly purge		neighbors known to reside on attached links and to quickly purge
	cached values that become invalid. Hosts also use Neighbor Discovery		cached values that become invalid. Hosts also use Neighbor Discovery
	to find neighboring routers that are willing to forward packets on		to find neighboring routers that are willing to forward packets on
	their behalf. Finally, nodes use the protocol to actively keep track		their behalf. Finally, nodes use the protocol to actively keep track
	of which neighbors are reachable and which are not, and to detect		of which neighbors are reachable and which are not, and to detect
	changed link-layer addresses. When a router or the path to a router		changed link-layer addresses. When a router or the path to a router
	fails, a host actively searches for functioning alternates.		fails, a host actively searches for functioning alternates.
	Unless specified otherwise (in a document that covers operating IP		Unless specified otherwise (in a document that covers operating IP
	over a particular link type) this document applies to all link types.		over a particular link type) this document applies to all link types.
	However, because ND uses link-layer multicast for some of its		However, because ND uses link-layer multicast for some of its
	services, it is possible that on some link types (e.g., NBMA links)		services, it is possible that on some link types (e.g., Non-Broadcast
	alternative protocols or mechanisms to implement those services will		Multi-Access (NBMA) links), alternative protocols or mechanisms to
	be specified (in the appropriate document covering the operation of		implement those services will be specified (in the appropriate
	IP over a particular link type). The services described in this		document covering the operation of IP over a particular link type).
	document that are not directly dependent on multicast, such as		The services described in this document that are not directly
	Redirects, Next-hop determination, Neighbor Unreachability Detection,		dependent on multicast, such as Redirects, Next-hop determination,
	etc., are expected to be provided as specified in this document. The		Neighbor Unreachability Detection, etc., are expected to be provided
	details of how one uses ND on NBMA links are addressed in [IPv6-		as specified in this document. The details of how one uses ND on
	NBMA]. In addition, [IPv6-3GPP] and [IPv6-CELL] discuss the use of		NBMA links are addressed in [IPv6-NBMA]. In addition, [IPv6-3GPP]
	this protocol over some cellular links, which are examples of NBMA		and[IPv6-CELL] discuss the use of this protocol over some cellular
	links.		links, which are examples of NBMA links.
	The authors of RFC 2461 would like to acknowledge the contributions
	of the IPv6 working group and, in particular, (in alphabetical order)
	Ran Atkinson, Jim Bound, Scott Bradner, Alex Conta, Stephen Deering,
	Richard Draves, Francis Dupont, Robert Elz, Robert Gilligan, Robert
	Hinden, Tatuya Jinmei, Allison Mankin, Dan McDonald, Charles Perkins,
	Matt Thomas, and Susan Thomson.
	The editor of this document (Hesham Soliman) would like to thank the
	ipv6 working group for the numerous contributions to this revision,
	in particular, (in alphabetical order), Greg Daley, Elwyn Davies,
	Ralph Droms, Brian Haberman, Bob Hinden, Tatuya Jinmei, Pekka Savola,
	Fred Templin and Christian Vogt.
	2. TERMINOLOGY		2. Terminology
	2.1. General		2.1. General
	IP - Internet Protocol Version 6. The terms IPv4 and		IP - Internet Protocol Version 6. The terms IPv4 and IPv6
	IPv6 are used only in contexts where necessary to avoid		are used only in contexts where necessary to avoid
	ambiguity.		ambiguity.
	ICMP - Internet Control Message Protocol for the Internet		ICMP - Internet Control Message Protocol for the Internet
	Protocol Version 6. The terms ICMPv4 and ICMPv6 are		Protocol Version 6. The terms ICMPv4 and ICMPv6 are
	used only in contexts where necessary to avoid		used only in contexts where necessary to avoid
	ambiguity.		ambiguity.
	node - a device that implements IP.		node - a device that implements IP.
	router - a node that forwards IP packets not explicitly		router - a node that forwards IP packets not explicitly
	addressed to itself.		addressed to itself.
	host - any node that is not a router.		host - any node that is not a router.
	upper layer - a protocol layer immediately above IP. Examples are		upper layer - a protocol layer immediately above IP. Examples are
	transport protocols such as TCP and UDP, control		transport protocols such as TCP and UDP, control
	protocols such as ICMP, routing protocols such as OSPF,		protocols such as ICMP, routing protocols such as OSPF,
	and internet or lower-layer protocols being "tunneled"		and Internet-layer (or lower-layer) protocols being
	over (i.e., encapsulated in) IP such as IPX, AppleTalk,		"tunneled" over (i.e., encapsulated in) IP such as
	or IP itself.		Internetwork Packet Exchange (IPX), AppleTalk, or IP
			itself.
	link - a communication facility or medium over which nodes can		link - a communication facility or medium over which nodes can
	communicate at the link-layer, i.e., the layer		communicate at the link layer, i.e., the layer
	immediately below IP. Examples are Ethernets (simple		immediately below IP. Examples are Ethernets (simple
	or bridged), PPP links, X.25, Frame Relay, or ATM		or bridged), PPP links, X.25, Frame Relay, or ATM
	networks as well as internet (or higher) layer		networks as well as Internet-layer (or higher-layer)
	"tunnels", such as tunnels over IPv4 or IPv6 itself.		"tunnels", such as tunnels over IPv4 or IPv6 itself.
	interface - a node's attachment to a link.		interface - a node's attachment to a link.
	neighbors - nodes attached to the same link.		neighbors - nodes attached to the same link.
	address - an IP-layer identifier for an interface or a set of		address - an IP-layer identifier for an interface or a set of
	interfaces.		interfaces.
	anycast address		anycast address
	skipping to change at page 5, line 50		skipping to change at page 6, line 9
	bits of an address.		bits of an address.
	link-layer address		link-layer address
	- a link-layer identifier for an interface. Examples		- a link-layer identifier for an interface. Examples
	include IEEE 802 addresses for Ethernet links.		include IEEE 802 addresses for Ethernet links.
	on-link - an address that is assigned to an interface on a		on-link - an address that is assigned to an interface on a
	specified link. A node considers an address to be on-		specified link. A node considers an address to be on-
	link if:		link if:
	- it is covered by one of the link's prefixes (e.g.		- it is covered by one of the link's prefixes (e.g.,
	as indicated by the on-link flag in the Prefix		as indicated by the on-link flag in the Prefix
	Information option), or		Information option), or
	- a neighboring router specifies the address as		- a neighboring router specifies the address as the
	the target of a Redirect message, or		target of a Redirect message, or
	- a Neighbor Advertisement message is received for		- a Neighbor Advertisement message is received for
	the (target) address, or		the (target) address, or
	- any Neighbor Discovery message is received from		- any Neighbor Discovery message is received from
	the address.		the address.
	off-link - the opposite of "on-link"; an address that is not		off-link - the opposite of "on-link"; an address that is not
	assigned to any interfaces on the specified link.		assigned to any interfaces on the specified link.
	longest prefix match		longest prefix match
	- The process of determining which prefix (if any) in		- the process of determining which prefix (if any) in a
	a set of prefixes covers a target address. A target		set of prefixes covers a target address. A target
	address is covered by a prefix if all of the bits in		address is covered by a prefix if all of the bits in
	the prefix match the left-most bits of the target		the prefix match the left-most bits of the target
	address. When multiple prefixes cover an address,		address. When multiple prefixes cover an address, the
	the longest prefix is the one that matches.		longest prefix is the one that matches.
	reachability		reachability
	- whether or not the one-way "forward" path to a		- whether or not the one-way "forward" path to a neighbor
	neighbor is functioning properly. In particular,		is functioning properly. In particular, whether
	whether packets sent to a neighbor are reaching the		packets sent to a neighbor are reaching the IP layer on
	IP layer on the neighboring machine and are being		the neighboring machine and are being processed
	processed properly by the receiving IP layer. For		properly by the receiving IP layer. For neighboring
	neighboring routers, reachability means that packets		routers, reachability means that packets sent by a
	sent by a node's IP layer are delivered to the		node's IP layer are delivered to the router's IP layer,
	router's IP layer, and the router is indeed		and the router is indeed forwarding packets (i.e., it
	forwarding packets (i.e., it is configured as a		is configured as a router, not a host). For hosts,
	router, not a host). For hosts, reachability means		reachability means that packets sent by a node's IP
	that packets sent by a node's IP layer are delivered		layer are delivered to the neighbor host's IP layer.
	to the neighbor host's IP layer.
	packet - an IP header plus payload.		packet - an IP header plus payload.
	link MTU - the maximum transmission unit, i.e., maximum packet		link MTU - the maximum transmission unit, i.e., maximum packet
	size in octets, that can be conveyed in one		size in octets, that can be conveyed in one
	transmission unit over a link.		transmission unit over a link.
	target - an address about which address resolution		target - an address about which address resolution information
	information is sought, or an address which is the		is sought, or an address that is the new first hop when
	new first-hop when being redirected.		being redirected.
	proxy - a node that responds to Neighbor Discovery query		proxy - a node that responds to Neighbor Discovery query
	messages on behalf of another node. A router acting		messages on behalf of another node. A router acting on
	on behalf of a mobile node that has moved off-link		behalf of a mobile node that has moved off-link could
	could potentially act as a proxy for the mobile		potentially act as a proxy for the mobile node.
	node.
	ICMP destination unreachable indication		ICMP destination unreachable indication
	- an error indication returned to the original sender		- an error indication returned to the original sender of
	of a packet that cannot be delivered for the reasons		a packet that cannot be delivered for the reasons
	outlined in [ICMPv6]. If the error occurs on a node		outlined in [ICMPv6]. If the error occurs on a node
	other than the node originating the packet, an ICMP		other than the node originating the packet, an ICMP
	error message is generated. If the error occurs on		error message is generated. If the error occurs on the
	the originating node, an implementation is not		originating node, an implementation is not required to
	required to actually create and send an ICMP error		actually create and send an ICMP error packet to the
	packet to the source, as long as the upper-layer		source, as long as the upper-layer sender is notified
	sender is notified through an appropriate mechanism		through an appropriate mechanism (e.g., return value
	(e.g., return value from a procedure call). Note,		from a procedure call). Note, however, that an
	however, that an implementation may find it		implementation may find it convenient in some cases to
	convenient in some cases to return errors to the		return errors to the sender by taking the offending
	sender by taking the offending packet, generating an		packet, generating an ICMP error message, and then
	ICMP error message, and then delivering it (locally)		delivering it (locally) through the generic error-
	through the generic error handling routines.		handling routines.
	random delay		random delay
	- when sending out messages, it is sometimes necessary to		- when sending out messages, it is sometimes necessary to
	delay a transmission for a random amount of time in		delay a transmission for a random amount of time in
	order to prevent multiple nodes from transmitting at		order to prevent multiple nodes from transmitting at
	exactly the same time, or to prevent long-range		exactly the same time, or to prevent long-range
	periodic transmissions from synchronizing with each		periodic transmissions from synchronizing with each
	other [SYNC]. When a random component is required, a		other [SYNC]. When a random component is required, a
	node calculates the actual delay in such a way that the		node calculates the actual delay in such a way that the
	computed delay forms a uniformly-distributed random		computed delay forms a uniformly distributed random
	value that falls between the specified minimum and		value that falls between the specified minimum and
	maximum delay times. The implementor must take care to		maximum delay times. The implementor must take care to
	insure that the granularity of the calculated random		ensure that the granularity of the calculated random
	component and the resolution of the timer used are both		component and the resolution of the timer used are both
	high enough to insure that the probability of multiple		high enough to ensure that the probability of multiple
	nodes delaying the same amount of time is small.		nodes delaying the same amount of time is small.
	random delay seed		random delay seed
	- If a pseudo-random number generator is used in		- if a pseudo-random number generator is used in
	calculating a random delay component, the generator		calculating a random delay component, the generator
	should be initialized with a unique seed prior to being		should be initialized with a unique seed prior to being
	used. Note that it is not sufficient to use the		used. Note that it is not sufficient to use the
	interface identifier alone as the seed, since interface		interface identifier alone as the seed, since interface
	identifiers will not always be unique. To reduce the		identifiers will not always be unique. To reduce the
	probability that duplicate interface identifiers cause		probability that duplicate interface identifiers cause
	the same seed to be used, the seed should be calculated		the same seed to be used, the seed should be calculated
	from a variety of input sources (e.g., machine		from a variety of input sources (e.g., machine
	components) that are likely to be different even on		components) that are likely to be different even on
	identical "boxes". For example, the seed could be		identical "boxes". For example, the seed could be
	formed by combining the CPU's serial number with an		formed by combining the CPU's serial number with an
	interface identifier. Additional information on		interface identifier. Additional information on
	randomness and random number generation can be found in		randomness and random number generation can be found in
	[RAND].		[RAND].
	2.2. Link Types		2.2. Link Types
	Different link-layers have different properties. The ones of concern		Different link layers have different properties. The ones of concern
	to Neighbor Discovery are:		to Neighbor Discovery are:
	multicast capable		multicast capable
	- a link that supports a native mechanism at the		- a link that supports a native mechanism at the link
	link-layer for sending packets to all (i.e.,		layer for sending packets to all (i.e., broadcast)
	broadcast) or a subset of all neighbors.		or a subset of all neighbors.
	point-to-point - a link that connects exactly two interfaces. A		point-to-point - a link that connects exactly two interfaces. A
	point-to-point link is assumed to have multicast		point-to-point link is assumed to have multicast
	capability and have a link-local address.		capability and a link-local address.
	non-broadcast multi-access (NBMA)		non-broadcast multi-access (NBMA)
	- a link to which more than two interfaces can attach,		- a link to which more than two interfaces can attach,
	but that does not support a native form of multicast		but that does not support a native form of multicast
	or broadcast (e.g., X.25, ATM, frame relay, etc.).		or broadcast (e.g., X.25, ATM, frame relay, etc.).
	Note that all link types (including NBMA) are		Note that all link types (including NBMA) are
	expected to provide multicast service for		expected to provide multicast service for
	applications that need it (e.g., using multicast		applications that need it (e.g., using multicast
	servers). However, it is an issue for further study		servers). However, it is an issue for further study
	whether ND should use such facilities or an		whether ND should use such facilities or an
	alternate mechanism that provides the equivalent		alternate mechanism that provides the equivalent
	multicast capability for ND.		multicast capability for ND.
	shared media - a link that allows direct communication among a		shared media - a link that allows direct communication among a
	number of nodes, but attached nodes are configured		number of nodes, but attached nodes are configured
	in such a way that they do not have complete prefix		in such a way that they do not have complete prefix
	information for all on-link destinations. That is,		information for all on-link destinations. That is,
	at the IP level, nodes on the same link may not know		at the IP level, nodes on the same link may not know
	that they are neighbors; by default, they		that they are neighbors; by default, they
	communicate through a router. Examples are large		communicate through a router. Examples are large
	(switched) public data networks such as SMDS and B-		(switched) public data networks such as Switched
	ISDN. Also known as "large clouds". See [SH-		Multimegabit Data Service (SMDS) and Broadband
	MEDIA].		Integrated Services Digital Network (B-ISDN). Also
			known as "large clouds". See [SH-MEDIA].
	variable MTU - a link that does not have a well-defined MTU (e.g.,		variable MTU - a link that does not have a well-defined MTU (e.g.,
	IEEE 802.5 token rings). Many links (e.g.,		IEEE 802.5 token rings). Many links (e.g.,
	Ethernet) have a standard MTU defined by the link-		Ethernet) have a standard MTU defined by the link-
	layer protocol or by the specific document		layer protocol or by the specific document
	describing how to run IP over the link-layer.		describing how to run IP over the link layer.
	asymmetric reachability		asymmetric reachability
	- a link where non-reflexive and/or non-transitive		- a link where non-reflexive and/or non-transitive
	reachability is part of normal operation. (Non-		reachability is part of normal operation. (Non-
	reflexive reachability means packets from A reach B		reflexive reachability means packets from A reach B,
	but packets from B don't reach A. Non-transitive		but packets from B don't reach A. Non-transitive
	reachability means packets from A reach B, and		reachability means packets from A reach B, and
	packets from B reach C, but packets from A don't		packets from B reach C, but packets from A don't
	reach C.) Many radio links exhibit these		reach C.) Many radio links exhibit these
	properties.		properties.
	2.3. Addresses		2.3. Addresses
	Neighbor Discovery makes use of a number of different addresses		Neighbor Discovery makes use of a number of different addresses
	defined in [ADDR-ARCH], including:		defined in [ADDR-ARCH], including:
	skipping to change at page 9, line 22		skipping to change at page 9, line 38
	FF02::1.		FF02::1.
	all-routers multicast address		all-routers multicast address
	- the link-local scope address to reach all routers,		- the link-local scope address to reach all routers,
	FF02::2.		FF02::2.
	solicited-node multicast address		solicited-node multicast address
	- a link-local scope multicast address that is computed		- a link-local scope multicast address that is computed
	as a function of the solicited target's address. The		as a function of the solicited target's address. The
	function is described in [ADDR-ARCH]. The function is		function is described in [ADDR-ARCH]. The function is
	chosen so that IP addresses which differ only in the		chosen so that IP addresses that differ only in the
	most significant bits, e.g., due to multiple		most significant bits, e.g., due to multiple prefixes
	prefixes associated with different providers, will map		associated with different providers, will map to the
	to the same solicited-node address thereby reducing the		same solicited-node address thereby reducing the number
	number of multicast addresses a node must join at the		of multicast addresses a node must join at the link
	link-layer.		layer.
	link-local address		link-local address
	- a unicast address having link-only scope that can be		- a unicast address having link-only scope that can be
	used to reach neighbors. All interfaces on routers		used to reach neighbors. All interfaces on routers
	MUST have a link-local address. Also, [ADDRCONF]		MUST have a link-local address. Also, [ADDRCONF]
	requires that interfaces on hosts have a link-local		requires that interfaces on hosts have a link-local
	address.		address.
	unspecified address		unspecified address
	- a reserved address value that indicates the lack of an		- a reserved address value that indicates the lack of an
	skipping to change at page 10, line 14		skipping to change at page 10, line 35
	This document also makes use of internal conceptual variables to		This document also makes use of internal conceptual variables to
	describe protocol behavior and external variables that an		describe protocol behavior and external variables that an
	implementation must allow system administrators to change. The		implementation must allow system administrators to change. The
	specific variable names, how their values change, and how their		specific variable names, how their values change, and how their
	settings influence protocol behavior are provided to demonstrate		settings influence protocol behavior are provided to demonstrate
	protocol behavior. An implementation is not required to have them in		protocol behavior. An implementation is not required to have them in
	the exact form described here, so long as its external behavior is		the exact form described here, so long as its external behavior is
	consistent with that described in this document.		consistent with that described in this document.
	3. PROTOCOL OVERVIEW		3. Protocol Overview
	This protocol solves a set of problems related to the interaction		This protocol solves a set of problems related to the interaction
	between nodes attached to the same link. It defines mechanisms for		between nodes attached to the same link. It defines mechanisms for
	solving each of the following problems:		solving each of the following problems:
	Router Discovery: How hosts locate routers that reside on an		Router Discovery: How hosts locate routers that reside on an
	attached link.		attached link.
	Prefix Discovery: How hosts discover the set of address prefixes		Prefix Discovery: How hosts discover the set of address prefixes
	that define which destinations are on-link for an		that define which destinations are on-link for an
	attached link. (Nodes use prefixes to distinguish		attached link. (Nodes use prefixes to distinguish
	destinations that reside on-link from those only		destinations that reside on-link from those only
	reachable through a router.)		reachable through a router.)
	Parameter Discovery: How a node learns such link parameters as the		Parameter Discovery: How a node learns link parameters (such as the
	link MTU or such Internet parameters as the hop limit		link MTU) or Internet parameters (such as the hop limit
	value to place in outgoing packets.		value) to place in outgoing packets.
	Address Autoconfiguration: Introduces the mechanisms needed in		Address Autoconfiguration: Introduces the mechanisms needed in
	order to allow nodes to configure an address for an		order to allow nodes to configure an address for an
	interface in a stateless manner. Stateless address		interface in a stateless manner. Stateless address
	autoconfiguration is specified in [ADDRCONF].		autoconfiguration is specified in [ADDRCONF].
	Address resolution: How nodes determine the link-layer address of		Address resolution: How nodes determine the link-layer address of
	an on-link destination (e.g., a neighbor) given only the		an on-link destination (e.g., a neighbor) given only the
	destination's IP address.		destination's IP address.
	skipping to change at page 10, line 54		skipping to change at page 11, line 26
	traffic for the destination should be sent. The next-		traffic for the destination should be sent. The next-
	hop can be a router or the destination itself.		hop can be a router or the destination itself.
	Neighbor Unreachability Detection: How nodes determine that a		Neighbor Unreachability Detection: How nodes determine that a
	neighbor is no longer reachable. For neighbors used as		neighbor is no longer reachable. For neighbors used as
	routers, alternate default routers can be tried. For		routers, alternate default routers can be tried. For
	both routers and hosts, address resolution can be		both routers and hosts, address resolution can be
	performed again.		performed again.
	Duplicate Address Detection: How a node determines whether or not		Duplicate Address Detection: How a node determines whether or not
	an address it wishes to use is already in use by		an address it wishes to use is already in use by another
	another node.		node.
	Redirect: How a router informs a host of a better first-hop node		Redirect: How a router informs a host of a better first-hop node
	to reach a particular destination.		to reach a particular destination.
	Neighbor Discovery defines five different ICMP packet types: A pair		Neighbor Discovery defines five different ICMP packet types: A pair
	of Router Solicitation and Router Advertisement messages, a pair of		of Router Solicitation and Router Advertisement messages, a pair of
	Neighbor Solicitation and Neighbor Advertisements messages, and a		Neighbor Solicitation and Neighbor Advertisements messages, and a
	Redirect message. The messages serve the following purpose:		Redirect message. The messages serve the following purpose:
	Router Solicitation: When an interface becomes enabled, hosts may		Router Solicitation: When an interface becomes enabled, hosts may
	send out Router Solicitations that request routers to		send out Router Solicitations that request routers to
	generate Router Advertisements immediately rather than		generate Router Advertisements immediately rather than
	at their next scheduled time.		at their next scheduled time.
	Router Advertisement: Routers advertise their presence together		Router Advertisement: Routers advertise their presence together
	with various link and Internet parameters either		with various link and Internet parameters either
	periodically, or in response to a Router Solicitation		periodically, or in response to a Router Solicitation
	message. Router Advertisements contain prefixes that		message. Router Advertisements contain prefixes that
	are used for determining whether another address		are used for determining whether another address shares
	shares the same link (on-link determination) and/or		the same link (on-link determination) and/or address
	address configuration, a suggested hop limit value, etc.		configuration, a suggested hop limit value, etc.
	Neighbor Solicitation: Sent by a node to determine the link-layer		Neighbor Solicitation: Sent by a node to determine the link-layer
	address of a neighbor, or to verify that a neighbor is		address of a neighbor, or to verify that a neighbor is
	still reachable via a cached link-layer address.		still reachable via a cached link-layer address.
	Neighbor Solicitations are also used for Duplicate		Neighbor Solicitations are also used for Duplicate
	Address Detection.		Address Detection.
	Neighbor Advertisement: A response to a Neighbor Solicitation		Neighbor Advertisement: A response to a Neighbor Solicitation
	message. A node may also send unsolicited Neighbor		message. A node may also send unsolicited Neighbor
	Advertisements to announce a link-layer address change.		Advertisements to announce a link-layer address change.
	skipping to change at page 12, line 5		skipping to change at page 12, line 34
	detect router failure; a separate Neighbor Unreachability Detection		detect router failure; a separate Neighbor Unreachability Detection
	algorithm provides failure detection.		algorithm provides failure detection.
	Router Advertisements contain a list of prefixes used for on-link		Router Advertisements contain a list of prefixes used for on-link
	determination and/or autonomous address configuration; flags		determination and/or autonomous address configuration; flags
	associated with the prefixes specify the intended uses of a		associated with the prefixes specify the intended uses of a
	particular prefix. Hosts use the advertised on-link prefixes to		particular prefix. Hosts use the advertised on-link prefixes to
	build and maintain a list that is used in deciding when a packet's		build and maintain a list that is used in deciding when a packet's
	destination is on-link or beyond a router. Note that a destination		destination is on-link or beyond a router. Note that a destination
	can be on-link even though it is not covered by any advertised on-		can be on-link even though it is not covered by any advertised on-
	link prefix. In such cases a router can send a Redirect informing		link prefix. In such cases, a router can send a Redirect informing
	the sender that the destination is a neighbor.		the sender that the destination is a neighbor.
	Router Advertisements (and per-prefix flags) allow routers to inform		Router Advertisements (and per-prefix flags) allow routers to inform
	hosts how to perform Address Autoconfiguration. For example, routers		hosts how to perform Address Autoconfiguration. For example, routers
	can specify whether hosts should use DHCPv6 and/or		can specify whether hosts should use DHCPv6 and/or autonomous
	autonomous (stateless) address configuration.		(stateless) address configuration.
	Router Advertisement messages also contain Internet parameters such		Router Advertisement messages also contain Internet parameters such
	as the hop limit that hosts should use in outgoing packets and,		as the hop limit that hosts should use in outgoing packets and,
	optionally, link parameters such as the link MTU. This facilitates		optionally, link parameters such as the link MTU. This facilitates
	centralized administration of critical parameters that can be set on		centralized administration of critical parameters that can be set on
	routers and automatically propagated to all attached hosts.		routers and automatically propagated to all attached hosts.
	Nodes accomplish address resolution by multicasting a Neighbor		Nodes accomplish address resolution by multicasting a Neighbor
	Solicitation that asks the target node to return its link-layer		Solicitation that asks the target node to return its link-layer
	address. Neighbor Solicitation messages are multicast to the		address. Neighbor Solicitation messages are multicast to the
	skipping to change at page 13, line 19		skipping to change at page 14, line 5
	delay may be somewhat longer.		delay may be somewhat longer.
	Inbound load balancing - Nodes with replicated interfaces may want		Inbound load balancing - Nodes with replicated interfaces may want
	to load balance the reception of incoming packets across		to load balance the reception of incoming packets across
	multiple network interfaces on the same link. Such nodes		multiple network interfaces on the same link. Such nodes
	have multiple link-layer addresses assigned to the same		have multiple link-layer addresses assigned to the same
	interface. For example, a single network driver could		interface. For example, a single network driver could
	represent multiple network interface cards as a single		represent multiple network interface cards as a single
	logical interface having multiple link-layer addresses.		logical interface having multiple link-layer addresses.
	Neighbor Discovery allows a router to perform Load balancing		Neighbor Discovery allows a router to perform load balancing
	for traffic addressed to itself by allowing routers to omit		for traffic addressed to itself by allowing routers to omit
	the source link-layer address from Router Advertisement		the source link-layer address from Router Advertisement
	packets, thereby forcing neighbors to use Neighbor		packets, thereby forcing neighbors to use Neighbor
	Solicitation messages to learn link-layer addresses of		Solicitation messages to learn link-layer addresses of
	routers. Returned Neighbor Advertisement messages can then		routers. Returned Neighbor Advertisement messages can then
	contain link-layer addresses that differ depending on, e.g.,		contain link-layer addresses that differ depending on, e.g.,
	who issued the solicitation. This specification does not		who issued the solicitation. This specification does not
	define a mechanism that allows hosts to Load-balance		define a mechanism that allows hosts to Load-balance incoming
	incoming packets. See [LD-SHRE].		packets. See [LD-SHRE].
	Anycast addresses - Anycast addresses identify one of a set of		Anycast addresses - Anycast addresses identify one of a set of
	nodes providing an equivalent service, and multiple nodes on		nodes providing an equivalent service, and multiple nodes on
	the same link may be configured to recognize the same Anycast		the same link may be configured to recognize the same anycast
	address. Neighbor Discovery handles anycasts by having nodes		address. Neighbor Discovery handles anycasts by having nodes
	expect to receive multiple Neighbor Advertisements for the		expect to receive multiple Neighbor Advertisements for the
	same target. All advertisements for anycast addresses are		same target. All advertisements for anycast addresses are
	tagged as being non-Override advertisements. A non-Override		tagged as being non-Override advertisements. A non-Override
	advertisement is one that does not update or replace the		advertisement is one that does not update or replace the
	information sent by another advertisement. These		information sent by another advertisement. These
	advertisements are discussed later in the context of Neighbor		advertisements are discussed later in the context of Neighbor
	advertisement messages. This invokes specific rules to		advertisement messages. This invokes specific rules to
	determine which of potentially multiple advertisements should		determine which of potentially multiple advertisements should
	be used.		be used.
	Proxy advertisements - A node willing to accept packets on behalf		Proxy advertisements - A node willing to accept packets on behalf
	of a target address that is unable to respond to Neighbor		of a target address that is unable to respond to Neighbor
	Solicitations can issue non-Override Neighbor Advertisements.		Solicitations can issue non-Override Neighbor Advertisements.
	Proxy advertisements are used by Mobile IPv6 home Agents to		Proxy advertisements are used by Mobile IPv6 Home Agents to
	defend mobile nodes' addresses when they move off-link.		defend mobile nodes' addresses when they move off-link.
	However, it is not intended as a general mechanism to handle		However, it is not intended as a general mechanism to handle
	nodes that, e.g., do not implement this protocol.		nodes that, e.g., do not implement this protocol.
	3.1. Comparison with IPv4		3.1. Comparison with IPv4
	The IPv6 Neighbor Discovery protocol corresponds to a combination of		The IPv6 Neighbor Discovery protocol corresponds to a combination of
	the IPv4 protocols ARP [ARP], ICMP Router Discovery [RDISC], and ICMP		the IPv4 protocols Address Resolution Protocol [ARP], ICMP Router
	Redirect [ICMPv4]. In IPv4 there is no generally agreed upon		Discovery [RDISC], and ICMP Redirect [ICMPv4]. In IPv4 there is no
	protocol or mechanism for Neighbor Unreachability Detection, although		generally agreed upon protocol or mechanism for Neighbor
	Hosts Requirements [HR-CL] does specify some possible algorithms for		Unreachability Detection, although the Hosts Requirements document
	Dead Gateway Detection (a subset of the problems Neighbor		[HR-CL] does specify some possible algorithms for Dead Gateway
	Unreachability Detection tackles).		Detection (a subset of the problems Neighbor Unreachability Detection
			tackles).
	The Neighbor Discovery protocol provides a multitude of improvements		The Neighbor Discovery protocol provides a multitude of improvements
	over the IPv4 set of protocols:		over the IPv4 set of protocols:
	Router Discovery is part of the base protocol set; there is no		Router Discovery is part of the base protocol set; there is no
	need for hosts to "snoop" the routing protocols.		need for hosts to "snoop" the routing protocols.
	Router advertisements carry link-layer addresses; no additional		Router Advertisements carry link-layer addresses; no additional
	packet exchange is needed to resolve the router's link-layer		packet exchange is needed to resolve the router's link-layer
	address.		address.
	Router advertisements carry prefixes for a link; there is no need		Router Advertisements carry prefixes for a link; there is no need
	to have a separate mechanism to configure the "netmask".		to have a separate mechanism to configure the "netmask".
	Router advertisements enable Address Autoconfiguration.		Router Advertisements enable Address Autoconfiguration.
	Routers can advertise an MTU for hosts to use on the link,		Routers can advertise an MTU for hosts to use on the link,
	ensuring that all nodes use the same MTU value on links lacking a		ensuring that all nodes use the same MTU value on links lacking a
	well-defined MTU.		well-defined MTU.
	Address resolution multicasts are "spread" over 16 million (2^24)		Address resolution multicasts are "spread" over 16 million (2^24)
	multicast addresses greatly reducing address resolution related		multicast addresses, greatly reducing address-resolution-related
	interrupts on nodes other than the target. Moreover, non-IPv6		interrupts on nodes other than the target. Moreover, non-IPv6
	machines should not be interrupted at all.		machines should not be interrupted at all.
	Redirects contain the link-layer address of the new first hop;		Redirects contain the link-layer address of the new first hop;
	separate address resolution is not needed upon receiving a		separate address resolution is not needed upon receiving a
	redirect.		redirect.
	Multiple prefixes can be associated with the same link. By		Multiple prefixes can be associated with the same link. By
	default, hosts learn all on-link prefixes from Router		default, hosts learn all on-link prefixes from Router
	Advertisements. However, routers may be configured to omit some		Advertisements. However, routers may be configured to omit some
	skipping to change at page 15, line 8		skipping to change at page 15, line 52
	specifying a next-hop that is not on-link according to the link's		specifying a next-hop that is not on-link according to the link's
	network mask. The IPv6 redirect mechanism is analogous to the		network mask. The IPv6 redirect mechanism is analogous to the
	XRedirect facility specified in [SH-MEDIA]. It is expected to be		XRedirect facility specified in [SH-MEDIA]. It is expected to be
	useful on non-broadcast and shared media links in which it is		useful on non-broadcast and shared media links in which it is
	undesirable or not possible for nodes to know all prefixes for		undesirable or not possible for nodes to know all prefixes for
	on-link destinations.		on-link destinations.
	Neighbor Unreachability Detection is part of the base, which		Neighbor Unreachability Detection is part of the base, which
	significantly improves the robustness of packet delivery in the		significantly improves the robustness of packet delivery in the
	presence of failing routers, partially failing or partitioned		presence of failing routers, partially failing or partitioned
	links and nodes that change their link-layer addresses. For		links, or nodes that change their link-layer addresses. For
	instance, mobile nodes can move off-link without losing any		instance, mobile nodes can move off-link without losing any
	connectivity due to stale ARP caches.		connectivity due to stale ARP caches.
	Unlike ARP, Neighbor Discovery detects half-link failures (using		Unlike ARP, Neighbor Discovery detects half-link failures (using
	Neighbor Unreachability Detection) and avoids sending traffic to		Neighbor Unreachability Detection) and avoids sending traffic to
	neighbors with which two-way connectivity is absent.		neighbors with which two-way connectivity is absent.
	Unlike in IPv4 Router Discovery the Router Advertisement messages		Unlike in IPv4 Router Discovery, the Router Advertisement messages
	do not contain a preference field. The preference field is not		do not contain a preference field. The preference field is not
	needed to handle routers of different "stability"; the Neighbor		needed to handle routers of different "stability"; the Neighbor
	Unreachability Detection will detect dead routers and switch to a		Unreachability Detection will detect dead routers and switch to a
	working one.		working one.
	The use of link-local addresses to uniquely identify routers (for		The use of link-local addresses to uniquely identify routers (for
	Router Advertisement and Redirect messages) makes it possible for		Router Advertisement and Redirect messages) makes it possible for
	hosts to maintain the router associations in the event of the site		hosts to maintain the router associations in the event of the site
	renumbering to use new global prefixes.		renumbering to use new global prefixes.
	By setting the Hop Limit to 255, Neighbor Discovery is immune to		By setting the Hop Limit to 255, Neighbor Discovery is immune to
	off-link senders that accidentally or intentionally send ND		off-link senders that accidentally or intentionally send ND
	messages. In IPv4 off-link senders can send both ICMP Redirects		messages. In IPv4, off-link senders can send both ICMP Redirects
	and Router Advertisement messages.		and Router Advertisement messages.
	Placing address resolution at the ICMP layer makes the protocol		Placing address resolution at the ICMP layer makes the protocol
	more media-independent than ARP and makes it possible to use		more media-independent than ARP and makes it possible to use
	generic IP layer authentication and security mechanisms as		generic IP-layer authentication and security mechanisms as
	appropriate.		appropriate.
	3.2. Supported Link Types		3.2. Supported Link Types
	Neighbor Discovery supports links with different properties. In the		Neighbor Discovery supports links with different properties. In the
	presence of certain properties only a subset of the ND protocol		presence of certain properties, only a subset of the ND protocol
	mechanisms are fully specified in this document:		mechanisms are fully specified in this document:
	point-to-point - Neighbor Discovery handles such links just like		point-to-point - Neighbor Discovery handles such links just like
	multicast links. (Multicast can be trivially		multicast links. (Multicast can be trivially
	provided on point-to-point links, and interfaces		provided on point-to-point links, and interfaces
	can be assigned link-local addresses.)		can be assigned link-local addresses.)
	multicast - Neighbor Discovery operates over multicast capable		multicast - Neighbor Discovery operates over multicast capable
	links as described in this document.		links as described in this document.
	non-broadcast multiple access (NBMA)		non-broadcast multiple access (NBMA)
	- Redirect, Neighbor Unreachability Detection and		- Redirect, Neighbor Unreachability Detection and
	next-hop determination should be implemented as		next-hop determination should be implemented as
	described in this document. Address resolution,		described in this document. Address resolution,
	and the mechanism for delivering Router		and the mechanism for delivering Router
	Solicitations and Advertisements on NBMA links is		Solicitations and Advertisements on NBMA links are
	not specified in this document. Note that if		not specified in this document. Note that if
	hosts support manual configuration of a list of		hosts support manual configuration of a list of
	default routers, hosts can dynamically acquire the		default routers, hosts can dynamically acquire the
	link-layer addresses for their neighbors from		link-layer addresses for their neighbors from
	Redirect messages.		Redirect messages.
	shared media - The Redirect message is modeled after the		shared media - The Redirect message is modeled after the
	XRedirect message in [SH-MEDIA] in order to		XRedirect message in [SH-MEDIA] in order to
	simplify use of the protocol on shared media		simplify use of the protocol on shared media
	links.		links.
	skipping to change at page 16, line 34		skipping to change at page 17, line 32
	of a host, which it needs to send redirect		of a host, which it needs to send redirect
	messages to the host.		messages to the host.
	- How a router determines that it is the first-		- How a router determines that it is the first-
	hop router for a received packet.		hop router for a received packet.
	The protocol is extensible (through the definition		The protocol is extensible (through the definition
	of new options) so that other solutions might be		of new options) so that other solutions might be
	possible in the future.		possible in the future.
	variable MTU - Neighbor Discovery allows routers to specify a MTU		variable MTU - Neighbor Discovery allows routers to specify an
	for the link, which all nodes then use. All nodes		MTU for the link, which all nodes then use. All
	on a link must use the same MTU (or Maximum		nodes on a link must use the same MTU (or Maximum
	Receive Unit) in order for multicast to work		Receive Unit) in order for multicast to work
	properly. Otherwise when multicasting, a sender,		properly. Otherwise, when multicasting, a sender,
	which can not know which nodes will receive the		which can not know which nodes will receive the
	packet, could not determine a minimum packet size		packet, could not determine a minimum packet size
	that all receivers can process (or Maximum Receive		that all receivers can process (or Maximum Receive
	Unit).		Unit).
	asymmetric reachability		asymmetric reachability
	- Neighbor Discovery detects the absence of		- Neighbor Discovery detects the absence of
	symmetric reachability; a node avoids paths to a		symmetric reachability; a node avoids paths to a
	neighbor with which it does not have symmetric		neighbor with which it does not have symmetric
	connectivity.		connectivity.
	The Neighbor Unreachability Detection will		The Neighbor Unreachability Detection will
	typically identify such half-links and the node		typically identify such half-links and the node
	will refrain from using them.		will refrain from using them.
	The protocol can presumably be extended in the		The protocol can presumably be extended in the
	future to find viable paths in environments that		future to find viable paths in environments that
	lack reflexive and transitive connectivity.		lack reflexive and transitive connectivity.
	3.3. Securing Neighbor Discovery messages		3.3. Securing Neighbor Discovery Messages
	Neighbor Discovery messages are needed for various functions. Several		Neighbor Discovery messages are needed for various functions.
	functions are designed to allow hosts to ascertain the ownership of		Several functions are designed to allow hosts to ascertain the
	an address or the mapping between link-layer and IP layer addresses.		ownership of an address or the mapping between link-layer and IP-
	Vulnerabilities related to Neighbor Discovery are discussed in		layer addresses. Vulnerabilities related to Neighbor Discovery are
	section 11.1. A general solution for securing Neighbor Discovery is		discussed in Section 11.1. A general solution for securing Neighbor
	outside the scope of this specification and is discussed in [SEND].		Discovery is outside the scope of this specification and is discussed
	However, Section 11.2 explains how and under which constraints IPsec		in [SEND]. However, Section 11.2 explains how and under which
	AH or ESP can be used to secure Neighbor Discovery.		constraints IPsec Authentication Header (AH) or Encapsulating
			Security Payload (ESP) can be used to secure Neighbor Discovery.
	4. MESSAGE FORMATS		4. Message Formats
	This section introduces message formats for all messages used in this		This section introduces message formats for all messages used in this
	specification.		specification.
	4.1. Router Solicitation Message Format		4.1. Router Solicitation Message Format
	Hosts send Router Solicitations in order to prompt routers to		Hosts send Router Solicitations in order to prompt routers to
	generate Router Advertisements quickly.		generate Router Advertisements quickly.
	0 1 2 3		0 1 2 3
	skipping to change at page 17, line 49		skipping to change at page 19, line 4
	Source Address		Source Address
	An IP address assigned to the sending interface, or		An IP address assigned to the sending interface, or
	the unspecified address if no address is assigned		the unspecified address if no address is assigned
	to the sending interface.		to the sending interface.
	Destination Address		Destination Address
	Typically the all-routers multicast address.		Typically the all-routers multicast address.
	Hop Limit 255		Hop Limit 255
	ICMP Fields:		ICMP Fields:
	Type 133		Type 133
	Code 0		Code 0
	Checksum The ICMP checksum. See [ICMPv6].		Checksum The ICMP checksum. See [ICMPv6].
	Reserved This field is unused. It MUST be initialized to		Reserved This field is unused. It MUST be initialized to
	zero by the sender and MUST be ignored by the		zero by the sender and MUST be ignored by the
	receiver.		receiver.
	Valid Options:		Valid Options:
	Source link-layer address		Source link-layer address The link-layer address of the sender, if
	The link-layer address of the sender, if known.		known. MUST NOT be included if the Source Address
	MUST NOT be included if the Source Address is the		is the unspecified address. Otherwise, it SHOULD
	unspecified address. Otherwise it SHOULD be		be included on link layers that have addresses.
	included on link-layers that have addresses.
	Future versions of this protocol may define new option types.		Future versions of this protocol may define new option types.
	Receivers MUST silently ignore any options they do not recognize		Receivers MUST silently ignore any options they do not recognize
	and continue processing the message.		and continue processing the message.
	4.2. Router Advertisement Message Format		4.2. Router Advertisement Message Format
	Routers send out Router Advertisement message periodically, or in		Routers send out Router Advertisement messages periodically, or in
	response to a Router Solicitation.		response to Router Solicitations.
	0 1 2 3		0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Type | Code | Checksum |		| Type | Code | Checksum |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Cur Hop Limit |M|O| Reserved | Router Lifetime |		| Cur Hop Limit |M|O| Reserved | Router Lifetime |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Reachable Time |		| Reachable Time |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	skipping to change at page 19, line 24		skipping to change at page 20, line 32
	means unspecified (by this router).		means unspecified (by this router).
	M 1-bit "Managed address configuration" flag. When		M 1-bit "Managed address configuration" flag. When
	set, it indicates that addresses are available via		set, it indicates that addresses are available via
	Dynamic Host Configuration Protocol [DHCPv6].		Dynamic Host Configuration Protocol [DHCPv6].
	If the M flag is set, the O flag is redundant and		If the M flag is set, the O flag is redundant and
	can be ignored because DHCPv6 will return all		can be ignored because DHCPv6 will return all
	available configuration information.		available configuration information.
	O 1-bit "Other configuration" flag. When		O 1-bit "Other configuration" flag. When set, it
	set, it indicates that other configuration		indicates that other configuration information is
	information is available via DHCPv6.		available via DHCPv6. Examples of such information
	Examples of such information are DNS-related		are DNS-related information or information on other
	information or information on other servers within		servers within the network.
	the network.
	Note: If neither M nor O flags are set this indicates that no		Note: If neither M nor O flags are set, this indicates that no
	information is available via DHCPv6.		information is available via DHCPv6.
	Reserved A 6-bit unused field. It MUST be initialized to		Reserved A 6-bit unused field. It MUST be initialized to
	zero by the sender and MUST be ignored by the		zero by the sender and MUST be ignored by the
	receiver.		receiver.
	Router Lifetime		Router Lifetime
	16-bit unsigned integer. The lifetime associated		16-bit unsigned integer. The lifetime associated
	with the default router in units of seconds.		with the default router in units of seconds. The
	The field can contain values up to 65535 and		field can contain values up to 65535 and receivers
	receivers should handle any value, while the		should handle any value, while the sending rules in
	sending rules in section 6 limit the lifetime to		Section 6 limit the lifetime to 9000 seconds. A
	9000 seconds. A Lifetime of 0 indicates that the		Lifetime of 0 indicates that the router is not a
	router is not a default router and SHOULD NOT		default router and SHOULD NOT appear on the default
	appear on the default router list. The Router		router list. The Router Lifetime applies only to
	Lifetime applies only to the router's usefulness as		the router's usefulness as a default router; it
	a default router; it does not apply to information		does not apply to information contained in other
	contained in other message fields or options.		message fields or options. Options that need time
	Options that need time limits for their information		limits for their information include their own
	include their own lifetime fields.		lifetime fields.
	Reachable Time 32-bit unsigned integer. The time, in		Reachable Time 32-bit unsigned integer. The time, in
	milliseconds, that a node assumes a neighbor is		milliseconds, that a node assumes a neighbor is
	reachable after having received a reachability		reachable after having received a reachability
	confirmation. Used by the Neighbor Unreachability		confirmation. Used by the Neighbor Unreachability
	Detection algorithm (see Section 7.3). A value of		Detection algorithm (see Section 7.3). A value of
	zero means unspecified (by this router).		zero means unspecified (by this router).
	Retrans Timer 32-bit unsigned integer. The time, in		Retrans Timer 32-bit unsigned integer. The time, in
	milliseconds, between retransmitted Neighbor		milliseconds, between retransmitted Neighbor
	Solicitation messages. Used by address resolution		Solicitation messages. Used by address resolution
	and the Neighbor Unreachability Detection algorithm		and the Neighbor Unreachability Detection algorithm
	(see Sections 7.2 and 7.3). A value of zero means		(see Sections 7.2 and 7.3). A value of zero means
	unspecified (by this router).		unspecified (by this router).
	Possible options:		Possible options:
	Source link-layer address		Source link-layer address
	The link-layer address of the interface from which		The link-layer address of the interface from which
	the Router Advertisement is sent. Only used on		the Router Advertisement is sent. Only used on
	link-layers that have addresses. A router MAY omit		link layers that have addresses. A router MAY omit
	this option in order to enable inbound load sharing		this option in order to enable inbound load sharing
	across multiple link-layer addresses.		across multiple link-layer addresses.
	MTU SHOULD be sent on links that have a variable MTU		MTU SHOULD be sent on links that have a variable MTU
	(as specified in the document that describes how to		(as specified in the document that describes how to
	run IP over the particular link type). MAY be sent		run IP over the particular link type). MAY be sent
	on other links.		on other links.
	Prefix Information		Prefix Information
	These options specify the prefixes that are on-link		These options specify the prefixes that are on-link
	skipping to change at page 21, line 39		skipping to change at page 23, line 4
	Either the solicited-node multicast address		Either the solicited-node multicast address
	corresponding to the target address, or the target		corresponding to the target address, or the target
	address.		address.
	Hop Limit 255		Hop Limit 255
	ICMP Fields:		ICMP Fields:
	Type 135		Type 135
	Code 0		Code 0
	Checksum The ICMP checksum. See [ICMPv6].		Checksum The ICMP checksum. See [ICMPv6].
	Reserved This field is unused. It MUST be initialized to		Reserved This field is unused. It MUST be initialized to
	zero by the sender and MUST be ignored by the		zero by the sender and MUST be ignored by the
	receiver.		receiver.
	Target Address		Target Address The IP address of the target of the solicitation.
	The IP address of the target of the solicitation.
	It MUST NOT be a multicast address.		It MUST NOT be a multicast address.
	Possible options:		Possible options:
	Source link-layer address		Source link-layer address
	The link-layer address for the sender. MUST NOT be		The link-layer address for the sender. MUST NOT be
	included when the source IP address is the		included when the source IP address is the
	unspecified address. Otherwise, on link-layers		unspecified address. Otherwise, on link layers
	that have addresses this option MUST be included in		that have addresses this option MUST be included in
	multicast solicitations and SHOULD be included in		multicast solicitations and SHOULD be included in
	unicast solicitations.		unicast solicitations.
	Future versions of this protocol may define new option types.		Future versions of this protocol may define new option types.
	Receivers MUST silently ignore any options they do not recognize		Receivers MUST silently ignore any options they do not recognize
	and continue processing the message.		and continue processing the message.
	4.4. Neighbor Advertisement Message Format		4.4. Neighbor Advertisement Message Format
	skipping to change at page 23, line 53		skipping to change at page 25, line 22
	prompted this advertisement. For an unsolicited		prompted this advertisement. For an unsolicited
	advertisement, the address whose link-layer address		advertisement, the address whose link-layer address
	has changed. The Target Address MUST NOT be a		has changed. The Target Address MUST NOT be a
	multicast address.		multicast address.
	Possible options:		Possible options:
	Target link-layer address		Target link-layer address
	The link-layer address for the target, i.e., the		The link-layer address for the target, i.e., the
	sender of the advertisement. This option MUST be		sender of the advertisement. This option MUST be
	included on link-layers that have addresses when		included on link layers that have addresses when
	responding to multicast solicitations. When		responding to multicast solicitations. When
	responding to a unicast Neighbor Solicitation this		responding to a unicast Neighbor Solicitation this
	option SHOULD be included.		option SHOULD be included.
	The option MUST be included for multicast		The option MUST be included for multicast
	solicitations in order to avoid infinite Neighbor		solicitations in order to avoid infinite Neighbor
	Solicitation "recursion" when the peer node does		Solicitation "recursion" when the peer node does
	not have a cache entry to return a Neighbor		not have a cache entry to return a Neighbor
	Advertisements message. When responding to unicast		Advertisements message. When responding to unicast
	solicitations, the option can be omitted since the		solicitations, the option can be omitted since the
	sender of the solicitation has the correct link-		sender of the solicitation has the correct link-
	layer address; otherwise it would not be able		layer address; otherwise, it would not be able to
	to send the unicast solicitation in the first		send the unicast solicitation in the first place.
	place. However, including the link-layer address in		However, including the link-layer address in this
	this case adds little overhead and eliminates a		case adds little overhead and eliminates a
	potential race condition where the sender deletes		potential race condition where the sender deletes
	the cached link-layer address prior to receiving a		the cached link-layer address prior to receiving a
	response to a previous solicitation.		response to a previous solicitation.
	Future versions of this protocol may define new option types.		Future versions of this protocol may define new option types.
	Receivers MUST silently ignore any options they do not recognize		Receivers MUST silently ignore any options they do not recognize
	and continue processing the message.		and continue processing the message.
	4.5. Redirect Message Format		4.5. Redirect Message Format
	skipping to change at page 25, line 33		skipping to change at page 27, line 16
	Type 137		Type 137
	Code 0		Code 0
	Checksum The ICMP checksum. See [ICMPv6].		Checksum The ICMP checksum. See [ICMPv6].
	Reserved This field is unused. It MUST be initialized to		Reserved This field is unused. It MUST be initialized to
	zero by the sender and MUST be ignored by the		zero by the sender and MUST be ignored by the
	receiver.		receiver.
	Target Address An IP address that is a better first hop to use for		Target Address
			An IP address that is a better first hop to use for
	the ICMP Destination Address. When the target is		the ICMP Destination Address. When the target is
	the actual endpoint of communication, i.e., the		the actual endpoint of communication, i.e., the
	destination is a neighbor, the Target Address field		destination is a neighbor, the Target Address field
	MUST contain the same value as the ICMP Destination		MUST contain the same value as the ICMP Destination
	Address field. Otherwise the target is a better		Address field. Otherwise, the target is a better
	first-hop router and the Target Address MUST be the		first-hop router and the Target Address MUST be the
	router's link-local address so that hosts can		router's link-local address so that hosts can
	uniquely identify routers.		uniquely identify routers.
	Destination Address		Destination Address
	The IP address of the destination which is		The IP address of the destination that is
	redirected to the target.		redirected to the target.
	Possible options:		Possible options:
	Target link-layer address		Target link-layer address
	The link-layer address for the target. It SHOULD		The link-layer address for the target. It SHOULD
	be included (if known). Note that on NBMA links,		be included (if known). Note that on NBMA links,
	hosts may rely on the presence of the Target Link-		hosts may rely on the presence of the Target Link-
	Layer Address option in Redirect messages as the		Layer Address option in Redirect messages as the
	means for determining the link-layer addresses of		means for determining the link-layer addresses of
	skipping to change at page 26, line 17		skipping to change at page 28, line 9
	Redirected Header		Redirected Header
	As much as possible of the IP packet that triggered		As much as possible of the IP packet that triggered
	the sending of the Redirect without making the		the sending of the Redirect without making the
	redirect packet exceed the minimum MTU specified in		redirect packet exceed the minimum MTU specified in
	[IPv6].		[IPv6].
	4.6. Option Formats		4.6. Option Formats
	Neighbor Discovery messages include zero or more options, some of		Neighbor Discovery messages include zero or more options, some of
	which may appear multiple times in the same message. Options should		which may appear multiple times in the same message. Options should
	be padded when necessary to ensure that they end on their natural 64-		be padded when necessary to ensure that they end on their natural
	bit boundaries. All options are of the form:		64-bit boundaries. All options are of the form:
	0 1 2 3		0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Type | Length | ... |		| Type | Length | ... |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	~ ... ~		~ ... ~
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Fields:		Fields:
	skipping to change at page 27, line 4		skipping to change at page 28, line 46
	silently discard an ND packet that contains an		silently discard an ND packet that contains an
	option with length zero.		option with length zero.
	4.6.1. Source/Target Link-layer Address		4.6.1. Source/Target Link-layer Address
	0 1 2 3		0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Type | Length | Link-Layer Address ...		| Type | Length | Link-Layer Address ...
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Fields:		Fields:
	Type		Type
	1 for Source Link-layer Address		1 for Source Link-layer Address
	2 for Target Link-layer Address		2 for Target Link-layer Address
	Length The length of the option (including the type and		Length The length of the option (including the type and
	length fields) in units of 8 octets. For example,		length fields) in units of 8 octets. For example,
	the length for IEEE 802 addresses is 1 [IPv6-		the length for IEEE 802 addresses is 1
	ETHER].		[IPv6-ETHER].
	Link-Layer Address		Link-Layer Address
	The variable length link-layer address.		The variable length link-layer address.
	The content and format of this field (including		The content and format of this field (including
	byte and bit ordering) is expected to be specified		byte and bit ordering) is expected to be specified
	in specific documents that describe how IPv6		in specific documents that describe how IPv6
	operates over different link-layers. For instance,		operates over different link layers. For instance,
	[IPv6-ETHER].		[IPv6-ETHER].
	Description		Description
	The Source Link-Layer Address option contains the		The Source Link-Layer Address option contains the
	link-layer address of the sender of the packet. It		link-layer address of the sender of the packet. It
	is used in the Neighbor Solicitation, Router		is used in the Neighbor Solicitation, Router
	Solicitation, and Router Advertisement packets.		Solicitation, and Router Advertisement packets.
	The Target Link-Layer Address option contains the		The Target Link-Layer Address option contains the
	link-layer address of the target. It is used in		link-layer address of the target. It is used in
	skipping to change at page 30, line 41		skipping to change at page 32, line 44
	Reserved This field is unused. It MUST be initialized to		Reserved This field is unused. It MUST be initialized to
	zero by the sender and MUST be ignored by the		zero by the sender and MUST be ignored by the
	receiver.		receiver.
	MTU 32-bit unsigned integer. The recommended MTU for		MTU 32-bit unsigned integer. The recommended MTU for
	the link.		the link.
	Description		Description
	The MTU option is used in Router Advertisement		The MTU option is used in Router Advertisement
	messages to insure that all nodes on a link use the		messages to ensure that all nodes on a link use the
	same MTU value in those cases where the link MTU is		same MTU value in those cases where the link MTU is
	not well known.		not well known.
	This option MUST be silently ignored for other		This option MUST be silently ignored for other
	Neighbor Discovery messages.		Neighbor Discovery messages.
	In configurations in which heterogeneous		In configurations in which heterogeneous
	technologies are bridged together, the maximum		technologies are bridged together, the maximum
	supported MTU may differ from one segment to		supported MTU may differ from one segment to
	another. If the bridges do not generate ICMP		another. If the bridges do not generate ICMP
	Packet Too Big messages, communicating nodes will		Packet Too Big messages, communicating nodes will
	be unable to use Path MTU to dynamically determine		be unable to use Path MTU to dynamically determine
	the appropriate MTU on a per-neighbor basis. In		the appropriate MTU on a per-neighbor basis. In
	such cases, routers can be configured to use the		such cases, routers can be configured to use the
	MTU option to specify the maximum MTU value that is		MTU option to specify the maximum MTU value that is
	supported by all segments.		supported by all segments.
	5. CONCEPTUAL MODEL OF A HOST		5. Conceptual Model of a Host
	This section describes a conceptual model of one possible data		This section describes a conceptual model of one possible data
	structure organization that hosts (and to some extent routers) will		structure organization that hosts (and, to some extent, routers) will
	maintain in interacting with neighboring nodes. The described		maintain in interacting with neighboring nodes. The described
	organization is provided to facilitate the explanation of how the		organization is provided to facilitate the explanation of how the
	Neighbor Discovery protocol should behave. This document does not		Neighbor Discovery protocol should behave. This document does not
	mandate that implementations adhere to this model as long as their		mandate that implementations adhere to this model as long as their
	external behavior is consistent with that described in this document.		external behavior is consistent with that described in this document.
	This model is only concerned with the aspects of host behavior		This model is only concerned with the aspects of host behavior
	directly related to Neighbor Discovery. In particular, it does not		directly related to Neighbor Discovery. In particular, it does not
	concern itself with such issues as source address selection or the		concern itself with such issues as source address selection or the
	selecting of an outgoing interface on a multihomed host.		selecting of an outgoing interface on a multihomed host.
	skipping to change at page 31, line 36		skipping to change at page 33, line 44
	each interface:		each interface:
	Neighbor Cache		Neighbor Cache
	- A set of entries about individual neighbors to		- A set of entries about individual neighbors to
	which traffic has been sent recently. Entries are		which traffic has been sent recently. Entries are
	keyed on the neighbor's on-link unicast IP address		keyed on the neighbor's on-link unicast IP address
	and contain such information as its link-layer		and contain such information as its link-layer
	address, a flag indicating whether the neighbor is		address, a flag indicating whether the neighbor is
	a router or a host (called IsRouter in this		a router or a host (called IsRouter in this
	document), a pointer to any queued packets waiting		document), a pointer to any queued packets waiting
	for address resolution to complete, etc.		for address resolution to complete, etc. A
	A Neighbor Cache entry also contains information		Neighbor Cache entry also contains information used
	used by the Neighbor Unreachability Detection		by the Neighbor Unreachability Detection algorithm,
	algorithm, including the reachability state, the		including the reachability state, the number of
	number of unanswered probes, and the time the next		unanswered probes, and the time the next Neighbor
	Neighbor Unreachability Detection event is		Unreachability Detection event is scheduled to take
	scheduled to take place.		place.
	Destination Cache		Destination Cache
	- A set of entries about destinations to which		- A set of entries about destinations to which
	traffic has been sent recently. The Destination		traffic has been sent recently. The Destination
	Cache includes both on-link and off-link		Cache includes both on-link and off-link
	destinations and provides a level of indirection		destinations and provides a level of indirection
	into the Neighbor Cache; the Destination Cache maps		into the Neighbor Cache; the Destination Cache maps
	a destination IP address to the IP address of the		a destination IP address to the IP address of the
	next-hop neighbor. This cache is updated with		next-hop neighbor. This cache is updated with
	information learned from Redirect messages.		information learned from Redirect messages.
	Implementations may find it convenient to store		Implementations may find it convenient to store
	additional information not directly related to		additional information not directly related to
	Neighbor Discovery in Destination Cache entries,		Neighbor Discovery in Destination Cache entries,
	such as the Path MTU (PMTU) and round trip timers		such as the Path MTU (PMTU) and round-trip timers
	maintained by transport protocols.		maintained by transport protocols.
	Prefix List - A list of the prefixes that define a set of		Prefix List - A list of the prefixes that define a set of
	addresses that are on-link. Prefix List entries		addresses that are on-link. Prefix List entries
	are created from information received in Router		are created from information received in Router
	Advertisements. Each entry has an associated		Advertisements. Each entry has an associated
	invalidation timer value (extracted from the		invalidation timer value (extracted from the
	advertisement) used to expire prefixes when they		advertisement) used to expire prefixes when they
	become invalid. A special "infinity" timer value		become invalid. A special "infinity" timer value
	specifies that a prefix remains valid forever,		specifies that a prefix remains valid forever,
	skipping to change at page 33, line 20		skipping to change at page 35, line 39
	reachable recently (within tens of seconds ago).		reachable recently (within tens of seconds ago).
	STALE The neighbor is no longer known to be reachable but		STALE The neighbor is no longer known to be reachable but
	until traffic is sent to the neighbor, no attempt		until traffic is sent to the neighbor, no attempt
	should be made to verify its reachability.		should be made to verify its reachability.
	DELAY The neighbor is no longer known to be reachable, and		DELAY The neighbor is no longer known to be reachable, and
	traffic has recently been sent to the neighbor.		traffic has recently been sent to the neighbor.
	Rather than probe the neighbor immediately, however,		Rather than probe the neighbor immediately, however,
	delay sending probes for a short while in order to		delay sending probes for a short while in order to
	give upper layer protocols a chance to provide		give upper-layer protocols a chance to provide
	reachability confirmation.		reachability confirmation.
	PROBE The neighbor is no longer known to be reachable, and		PROBE The neighbor is no longer known to be reachable, and
	unicast Neighbor Solicitation probes are being sent to		unicast Neighbor Solicitation probes are being sent to
	verify reachability.		verify reachability.
	5.2. Conceptual Sending Algorithm		5.2. Conceptual Sending Algorithm
	When sending a packet to a destination, a node uses a combination of		When sending a packet to a destination, a node uses a combination of
	the Destination Cache, the Prefix List, and the Default Router List		the Destination Cache, the Prefix List, and the Default Router List
	skipping to change at page 34, line 13		skipping to change at page 36, line 42
	neighbor. If no entry exists, the sender creates one, sets its state		neighbor. If no entry exists, the sender creates one, sets its state
	to INCOMPLETE, initiates Address Resolution, and then queues the data		to INCOMPLETE, initiates Address Resolution, and then queues the data
	packet pending completion of address resolution. For multicast-		packet pending completion of address resolution. For multicast-
	capable interfaces Address Resolution consists of sending a Neighbor		capable interfaces Address Resolution consists of sending a Neighbor
	Solicitation message and waiting for a Neighbor Advertisement. When		Solicitation message and waiting for a Neighbor Advertisement. When
	a Neighbor Advertisement response is received, the link-layer		a Neighbor Advertisement response is received, the link-layer
	addresses is entered in the Neighbor Cache entry and the queued		addresses is entered in the Neighbor Cache entry and the queued
	packet is transmitted. The address resolution mechanism is described		packet is transmitted. The address resolution mechanism is described
	in detail in Section 7.2.		in detail in Section 7.2.
	For multicast packets the next-hop is always the (multicast)		For multicast packets, the next-hop is always the (multicast)
	destination address and is considered to be on-link. The procedure		destination address and is considered to be on-link. The procedure
	for determining the link-layer address corresponding to a given IP		for determining the link-layer address corresponding to a given IP
	multicast address can be found in a separate document that covers		multicast address can be found in a separate document that covers
	operating IP over a particular link type (e.g., [IPv6-ETHER]).		operating IP over a particular link type (e.g., [IPv6-ETHER]).
	Each time a Neighbor Cache entry is accessed while transmitting a		Each time a Neighbor Cache entry is accessed while transmitting a
	unicast packet, the sender checks Neighbor Unreachability Detection		unicast packet, the sender checks Neighbor Unreachability Detection
	related information according to the Neighbor Unreachability		related information according to the Neighbor Unreachability
	Detection algorithm (Section 7.3). This unreachability check might		Detection algorithm (Section 7.3). This unreachability check might
	result in the sender transmitting a unicast Neighbor Solicitation to		result in the sender transmitting a unicast Neighbor Solicitation to
	skipping to change at page 34, line 39		skipping to change at page 37, line 25
	used. If at some point communication ceases to proceed, as		used. If at some point communication ceases to proceed, as
	determined by the Neighbor Unreachability Detection algorithm, next-		determined by the Neighbor Unreachability Detection algorithm, next-
	hop determination may need to be performed again. For example,		hop determination may need to be performed again. For example,
	traffic through a failed router should be switched to a working		traffic through a failed router should be switched to a working
	router. Likewise, it may be possible to reroute traffic destined for		router. Likewise, it may be possible to reroute traffic destined for
	a mobile node to a "mobility agent".		a mobile node to a "mobility agent".
	Note that when a node redoes next-hop determination there is no need		Note that when a node redoes next-hop determination there is no need
	to discard the complete Destination Cache entry. In fact, it is		to discard the complete Destination Cache entry. In fact, it is
	generally beneficial to retain such cached information as the PMTU		generally beneficial to retain such cached information as the PMTU
	and round trip timer values that may also be kept in the Destination		and round-trip timer values that may also be kept in the Destination
	Cache entry.		Cache entry.
	Routers and multihomed hosts have multiple interfaces. The remainder		Routers and multihomed hosts have multiple interfaces. The remainder
	of this document assumes that all sent and received Neighbor		of this document assumes that all sent and received Neighbor
	Discovery messages refer to the interface of appropriate context.		Discovery messages refer to the interface of appropriate context.
	For example, when responding to a Router Solicitation, the		For example, when responding to a Router Solicitation, the
	corresponding Router Advertisement is sent out the interface on which		corresponding Router Advertisement is sent out the interface on which
	the solicitation was received.		the solicitation was received.
	5.3. Garbage Collection and Timeout Requirements		5.3. Garbage Collection and Timeout Requirements
	The conceptual data structures described above use different		The conceptual data structures described above use different
	mechanisms for discarding potentially stale or unused information.		mechanisms for discarding potentially stale or unused information.
	From the perspective of correctness there is no need to periodically		From the perspective of correctness, there is no need to periodically
	purge Destination and Neighbor Cache entries. Although stale		purge Destination and Neighbor Cache entries. Although stale
	information can potentially remain in the cache indefinitely, the		information can potentially remain in the cache indefinitely, the
	Neighbor Unreachability Detection algorithm ensures that stale		Neighbor Unreachability Detection algorithm ensures that stale
	information is purged quickly if it is actually being used.		information is purged quickly if it is actually being used.
	To limit the storage needed for the Destination and Neighbor Caches,		To limit the storage needed for the Destination and Neighbor Caches,
	a node may need to garbage-collect old entries. However, care must		a node may need to garbage-collect old entries. However, care must
	be taken to insure that sufficient space is always present to hold		be taken to ensure that sufficient space is always present to hold
	the working set of active entries. A small cache may result in an		the working set of active entries. A small cache may result in an
	excessive number of Neighbor Discovery messages if entries are		excessive number of Neighbor Discovery messages if entries are
	discarded and rebuilt in quick succession. Any LRU-based policy that		discarded and rebuilt in quick succession. Any Least Recently Used
	only reclaims entries that have not been used in some time (e.g., ten		(LRU)-based policy that only reclaims entries that have not been used
	minutes or more) should be adequate for garbage-collecting unused		in some time (e.g., ten minutes or more) should be adequate for
	entries.		garbage-collecting unused entries.
	A node should retain entries in the Default Router List and the		A node should retain entries in the Default Router List and the
	Prefix List until their lifetimes expire. However, a node may		Prefix List until their lifetimes expire. However, a node may
	garbage collect entries prematurely if it is low on memory. If not		garbage-collect entries prematurely if it is low on memory. If not
	all routers are kept on the Default Router list, a node should retain		all routers are kept on the Default Router list, a node should retain
	at least two entries in the Default Router List (and preferably more)		at least two entries in the Default Router List (and preferably more)
	in order to maintain robust connectivity for off-link destinations.		in order to maintain robust connectivity for off-link destinations.
	When removing an entry from the Prefix List there is no need to purge		When removing an entry from the Prefix List, there is no need to
	any entries from the Destination or Neighbor Caches. Neighbor		purge any entries from the Destination or Neighbor Caches. Neighbor
	Unreachability Detection will efficiently purge any entries in these		Unreachability Detection will efficiently purge any entries in these
	caches that have become invalid. When removing an entry from the		caches that have become invalid. When removing an entry from the
	Default Router List, however, any entries in the Destination Cache		Default Router List, however, any entries in the Destination Cache
	that go through that router must perform next-hop determination again		that go through that router must perform next-hop determination again
	to select a new default router.		to select a new default router.
	6. ROUTER AND PREFIX DISCOVERY		6. Router and Prefix Discovery
	This section describes router and host behavior related to the Router		This section describes router and host behavior related to the Router
	Discovery portion of Neighbor Discovery. Router Discovery is used to		Discovery portion of Neighbor Discovery. Router Discovery is used to
	locate neighboring routers as well as learn prefixes and		locate neighboring routers as well as learn prefixes and
	configuration parameters related to stateless address		configuration parameters related to stateless address
	autoconfiguration.		autoconfiguration.
	Prefix Discovery is the process through which hosts learn the ranges		Prefix Discovery is the process through which hosts learn the ranges
	of IP addresses that reside on-link and can be reached directly		of IP addresses that reside on-link and can be reached directly
	without going through a router. Routers send Router Advertisements		without going through a router. Routers send Router Advertisements
	skipping to change at page 37, line 42		skipping to change at page 40, line 42
	A router MUST allow for the following conceptual variables to be		A router MUST allow for the following conceptual variables to be
	configured by system management. The specific variable names are		configured by system management. The specific variable names are
	used for demonstration purposes only, and an implementation is not		used for demonstration purposes only, and an implementation is not
	required to have them, so long as its external behavior is consistent		required to have them, so long as its external behavior is consistent
	with that described in this document. Default values are specified		with that described in this document. Default values are specified
	to simplify configuration in common cases.		to simplify configuration in common cases.
	The default values for some of the variables listed below may be		The default values for some of the variables listed below may be
	overridden by specific documents that describe how IPv6 operates over		overridden by specific documents that describe how IPv6 operates over
	different link-layers. This rule simplifies the configuration of		different link layers. This rule simplifies the configuration of
	Neighbor Discovery over link types with widely differing performance		Neighbor Discovery over link types with widely differing performance
	characteristics.		characteristics.
	For each interface:		For each interface:
	IsRouter A flag indicating whether routing is enabled on		IsRouter A flag indicating whether routing is enabled on
	this interface. Enabling routing on the interface		this interface. Enabling routing on the interface
	would imply that a router can forward packets		would imply that a router can forward packets to or
	to or from the interface.		from the interface.
	Default: FALSE		Default: FALSE
	AdvSendAdvertisements		AdvSendAdvertisements
	A flag indicating whether or not the router sends		A flag indicating whether or not the router sends
	periodic Router Advertisements and responds to		periodic Router Advertisements and responds to
	Router Solicitations.		Router Solicitations.
	Default: FALSE		Default: FALSE
	skipping to change at page 38, line 31		skipping to change at page 41, line 42
	Default: 600 seconds		Default: 600 seconds
	MinRtrAdvInterval		MinRtrAdvInterval
	The minimum time allowed between sending		The minimum time allowed between sending
	unsolicited multicast Router Advertisements from		unsolicited multicast Router Advertisements from
	the interface, in seconds. MUST be no less than 3		the interface, in seconds. MUST be no less than 3
	seconds and no greater than .75 *		seconds and no greater than .75 *
	MaxRtrAdvInterval.		MaxRtrAdvInterval.
	Default: 0.33 * MaxRtrAdvInterval		Default: 0.33 * MaxRtrAdvInterval If
	If MaxRtrAdvInterval >= 9 seconds, otherwise the		MaxRtrAdvInterval >= 9 seconds; otherwise, the
	Default is MaxRtrAdvInterval.		Default is MaxRtrAdvInterval.
	AdvManagedFlag		AdvManagedFlag
	The TRUE/FALSE value to be placed in the "Managed		The TRUE/FALSE value to be placed in the "Managed
	address configuration" flag field in the Router		address configuration" flag field in the Router
	Advertisement. See [ADDRCONF].		Advertisement. See [ADDRCONF].
	Default: FALSE		Default: FALSE
	AdvOtherConfigFlag		AdvOtherConfigFlag
	The TRUE/FALSE value to be placed in the "Other		The TRUE/FALSE value to be placed in the "Other
	configuration" flag field in the Router		configuration" flag field in the Router
	Advertisement. See [ADDRCONF].		Advertisement. See [ADDRCONF].
	Default: FALSE		Default: FALSE
	AdvLinkMTU The value to be placed in MTU options sent by the		AdvLinkMTU The value to be placed in MTU options sent by the
	router. A value of zero indicates that no MTU		router. A value of zero indicates that no MTU
	options are sent.		options are sent.
	skipping to change at page 39, line 23		skipping to change at page 42, line 36
	AdvRetransTimer The value to be placed in the Retrans Timer field		AdvRetransTimer The value to be placed in the Retrans Timer field
	in the Router Advertisement messages sent by the		in the Router Advertisement messages sent by the
	router. The value zero means unspecified (by this		router. The value zero means unspecified (by this
	router).		router).
	Default: 0		Default: 0
	AdvCurHopLimit		AdvCurHopLimit
	The default value to be placed in the Cur Hop Limit		The default value to be placed in the Cur Hop Limit
	field in the Router Advertisement messages sent by		field in the Router Advertisement messages sent by
	the router. The value should be set to the		the router. The value should be set to the current
	current diameter of the Internet. The value zero		diameter of the Internet. The value zero means
	means unspecified (by this router).		unspecified (by this router).
	Default: The value specified in the "Assigned		Default: The value specified in the "Assigned
	Numbers" RFC [ASSIGNED] that was in effect at the		Numbers" [ASSIGNED] that was in effect at the time
	time of implementation.		of implementation.
	AdvDefaultLifetime		AdvDefaultLifetime
	The value to be placed in the Router Lifetime field		The value to be placed in the Router Lifetime field
	of Router Advertisements sent from the interface,		of Router Advertisements sent from the interface,
	in seconds. MUST be either zero or between		in seconds. MUST be either zero or between
	MaxRtrAdvInterval and 9000 seconds. A value of		MaxRtrAdvInterval and 9000 seconds. A value of
	zero indicates that the router is not to be used as		zero indicates that the router is not to be used as
	a default router.		a default router. These limits may be overridden
			by specific documents that describe how IPv6
			operates over different link layers. For instance,
			in a point-to-point link the peers may have enough
			information about the number and status of devices
			at the other end so that advertisements are needed
			less frequently.
	Default: 3 * MaxRtrAdvInterval		Default: 3 * MaxRtrAdvInterval
	AdvPrefixList		AdvPrefixList
	A list of prefixes to be placed in Prefix		A list of prefixes to be placed in Prefix
	Information options in Router Advertisement		Information options in Router Advertisement
	messages sent from the interface.		messages sent from the interface.
	Default: all prefixes that the router advertises		Default: all prefixes that the router advertises
	via routing protocols as being on-link for the		via routing protocols as being on-link for the
	interface from which the advertisement is sent.		interface from which the advertisement is sent.
	The link-local prefix SHOULD NOT be included in the		The link-local prefix SHOULD NOT be included in the
	list of advertised prefixes.		list of advertised prefixes.
	Each prefix has an associated:		Each prefix has an associated:
	AdvValidLifetime		AdvValidLifetime
	The value to be placed in the Valid		The value to be placed in the Valid
	Lifetime in the Prefix Information		Lifetime in the Prefix Information option,
	option, in seconds. The designated value		in seconds. The designated value of all
	of all 1's (0xffffffff) represents		1's (0xffffffff) represents infinity.
	infinity. Implementations MAY allow		Implementations MAY allow AdvValidLifetime
	AdvValidLifetime to be specified in two		to be specified in two ways:
	ways:
	- a time that decrements in real time,		- a time that decrements in real time,
	that is, one that will result in a		that is, one that will result in a
	Lifetime of zero at the specified		Lifetime of zero at the specified time
	time in the future, or		in the future, or
	- a fixed time that stays the same in		- a fixed time that stays the same in
	consecutive advertisements.		consecutive advertisements.
	Default: 2592000 seconds (30 days), fixed		Default: 2592000 seconds (30 days), fixed
	(i.e., stays the same in consecutive		(i.e., stays the same in consecutive
	advertisements).		advertisements).
	AdvOnLinkFlag		AdvOnLinkFlag
	The value to be placed in the on-link		The value to be placed in the on-link flag
	flag ("L-bit") field in the Prefix		("L-bit") field in the Prefix Information
	Information option.		option.
	Default: TRUE		Default: TRUE
	Stateless address configuration [ADDRCONF]		Stateless address configuration [ADDRCONF] defines
	defines additional information associated with		additional information associated with each of the
	each the prefixes:		prefixes:
	AdvPreferredLifetime		AdvPreferredLifetime
	The value to be placed in the Preferred		The value to be placed in the Preferred
	Lifetime in the Prefix Information		Lifetime in the Prefix Information option,
	option, in seconds. The designated value		in seconds. The designated value of all
	of all 1's (0xffffffff) represents		1's (0xffffffff) represents infinity. See
	infinity. See [ADDRCONF] for details on		[ADDRCONF] for details on how this value is
	how this value is used. Implementations		used. Implementations MAY allow
	MAY allow AdvPreferredLifetime to be		AdvPreferredLifetime to be specified in two
	specified in two ways:		ways:
	- a time that decrements in real time,		- a time that decrements in real time,
	that is, one that will result in a		that is, one that will result in a
	Lifetime of zero at a specified time		Lifetime of zero at a specified time in
	in the future, or		the future, or
	- a fixed time that stays the same in		- a fixed time that stays the same in
	consecutive advertisements.		consecutive advertisements.
	Default: 604800 seconds (7 days), fixed		Default: 604800 seconds (7 days), fixed
	(i.e., stays the same in consecutive		(i.e., stays the same in consecutive
	advertisements). This value MUST NOT be		advertisements). This value MUST NOT be
	larger than AdvValidLifetime.		larger than AdvValidLifetime.
	AdvAutonomousFlag		AdvAutonomousFlag
	skipping to change at page 41, line 29		skipping to change at page 45, line 11
	CurHopLimit, RetransTimer, and ReachableTime) apply to all nodes		CurHopLimit, RetransTimer, and ReachableTime) apply to all nodes
	including routers. In practice, these variables may not actually be		including routers. In practice, these variables may not actually be
	present on routers, since their contents can be derived from the		present on routers, since their contents can be derived from the
	variables described above. However, external router behavior MUST be		variables described above. However, external router behavior MUST be
	the same as host behavior with respect to these variables. In		the same as host behavior with respect to these variables. In
	particular, this includes the occasional randomization of the		particular, this includes the occasional randomization of the
	ReachableTime value as described in Section 6.3.2.		ReachableTime value as described in Section 6.3.2.
	Protocol constants are defined in Section 10.		Protocol constants are defined in Section 10.
	6.2.2. Becoming An Advertising Interface		6.2.2. Becoming an Advertising Interface
	The term "advertising interface" refers to any functioning and		The term "advertising interface" refers to any functioning and
	enabled interface that has at least one unicast IP address		enabled interface that has at least one unicast IP address assigned
	assigned to it and whose corresponding AdvSendAdvertisements flag is		to it and whose corresponding AdvSendAdvertisements flag is TRUE. A
	TRUE. A router MUST NOT send Router Advertisements out any interface		router MUST NOT send Router Advertisements out any interface that is
	that is not an advertising interface.		not an advertising interface.
	An interface may become an advertising interface at times other than		An interface may become an advertising interface at times other than
	system startup. For example:		system startup. For example:
	- changing the AdvSendAdvertisements flag on an enabled interface		- changing the AdvSendAdvertisements flag on an enabled interface
	from FALSE to TRUE, or		from FALSE to TRUE, or
	- administratively enabling the interface, if it had been		- administratively enabling the interface, if it had been
	administratively disabled, and its AdvSendAdvertisements flag is		administratively disabled, and its AdvSendAdvertisements flag is
	TRUE, or		TRUE, or
	skipping to change at page 42, line 35		skipping to change at page 46, line 22
	AdvRetransTimer.		AdvRetransTimer.
	- In the options:		- In the options:
	o Source Link-Layer Address option: link-layer address of the		o Source Link-Layer Address option: link-layer address of the
	sending interface. This option MAY be omitted to		sending interface. This option MAY be omitted to
	facilitate in-bound load balancing over replicated		facilitate in-bound load balancing over replicated
	interfaces.		interfaces.
	o MTU option: the interface's configured AdvLinkMTU value if		o MTU option: the interface's configured AdvLinkMTU value if
	the value is non-zero. If AdvLinkMTU is zero the MTU		the value is non-zero. If AdvLinkMTU is zero, the MTU
	option is not sent.		option is not sent.
	o Prefix Information options: one Prefix Information option		o Prefix Information options: one Prefix Information option
	for each prefix listed in AdvPrefixList with the option		for each prefix listed in AdvPrefixList with the option
	fields set from the information in the AdvPrefixList entry		fields set from the information in the AdvPrefixList entry
	as follows:		as follows:
	- In the "on-link" flag: the entry's AdvOnLinkFlag.		- In the "on-link" flag: the entry's AdvOnLinkFlag.
	- In the Valid Lifetime field: the entry's		- In the Valid Lifetime field: the entry's
	skipping to change at page 43, line 31		skipping to change at page 47, line 21
	6.2.4. Sending Unsolicited Router Advertisements		6.2.4. Sending Unsolicited Router Advertisements
	A host MUST NOT send Router Advertisement messages at any time.		A host MUST NOT send Router Advertisement messages at any time.
	Unsolicited Router Advertisements are not strictly periodic: the		Unsolicited Router Advertisements are not strictly periodic: the
	interval between subsequent transmissions is randomized to reduce the		interval between subsequent transmissions is randomized to reduce the
	probability of synchronization with the advertisements from other		probability of synchronization with the advertisements from other
	routers on the same link [SYNC]. Each advertising interface has its		routers on the same link [SYNC]. Each advertising interface has its
	own timer. Whenever a multicast advertisement is sent from an		own timer. Whenever a multicast advertisement is sent from an
	interface, the timer is reset to a uniformly-distributed random value		interface, the timer is reset to a uniformly distributed random value
	between the interface's configured MinRtrAdvInterval and		between the interface's configured MinRtrAdvInterval and
	MaxRtrAdvInterval; expiration of the timer causes the next		MaxRtrAdvInterval; expiration of the timer causes the next
	advertisement to be sent and a new random value to be chosen.		advertisement to be sent and a new random value to be chosen.
	For the first few advertisements (up to		For the first few advertisements (up to
	MAX_INITIAL_RTR_ADVERTISEMENTS) sent from an interface when it		MAX_INITIAL_RTR_ADVERTISEMENTS) sent from an interface when it
	becomes an advertising interface, if the randomly chosen interval is		becomes an advertising interface, if the randomly chosen interval is
	greater than MAX_INITIAL_RTR_ADVERT_INTERVAL, the timer SHOULD be set		greater than MAX_INITIAL_RTR_ADVERT_INTERVAL, the timer SHOULD be set
	to MAX_INITIAL_RTR_ADVERT_INTERVAL instead. Using a smaller interval		to MAX_INITIAL_RTR_ADVERT_INTERVAL instead. Using a smaller interval
	for the initial advertisements increases the likelihood of a router		for the initial advertisements increases the likelihood of a router
	skipping to change at page 43, line 53		skipping to change at page 47, line 43
	presence of possible packet loss.		presence of possible packet loss.
	The information contained in Router Advertisements may change through		The information contained in Router Advertisements may change through
	actions of system management. For instance, the lifetime of		actions of system management. For instance, the lifetime of
	advertised prefixes may change, new prefixes could be added, a router		advertised prefixes may change, new prefixes could be added, a router
	could cease to be a router (i.e., switch from being a router to being		could cease to be a router (i.e., switch from being a router to being
	a host), etc. In such cases, the router MAY transmit up to		a host), etc. In such cases, the router MAY transmit up to
	MAX_INITIAL_RTR_ADVERTISEMENTS unsolicited advertisements, using the		MAX_INITIAL_RTR_ADVERTISEMENTS unsolicited advertisements, using the
	same rules as when an interface becomes an advertising interface.		same rules as when an interface becomes an advertising interface.
	6.2.5. Ceasing To Be An Advertising Interface		6.2.5. Ceasing To Be an Advertising Interface
	An interface may cease to be an advertising interface, through		An interface may cease to be an advertising interface, through
	actions of system management such as:		actions of system management such as:
	- changing the AdvSendAdvertisements flag of an enabled interface		- changing the AdvSendAdvertisements flag of an enabled interface
	from TRUE to FALSE, or		from TRUE to FALSE, or
	- administratively disabling the interface, or		- administratively disabling the interface, or
	- shutting down the system.		- shutting down the system.
	In such cases the router SHOULD transmit one or more (but not more		In such cases, the router SHOULD transmit one or more (but not more
	than MAX_FINAL_RTR_ADVERTISEMENTS) final multicast Router		than MAX_FINAL_RTR_ADVERTISEMENTS) final multicast Router
	Advertisements on the interface with a Router Lifetime field of zero.		Advertisements on the interface with a Router Lifetime field of zero.
	In the case of a router becoming a host, the system SHOULD also		In the case of a router becoming a host, the system SHOULD also
	depart from the all-routers IP multicast group on all interfaces on		depart from the all-routers IP multicast group on all interfaces on
	which the router supports IP multicast (whether or not they had been		which the router supports IP multicast (whether or not they had been
	advertising interfaces). In addition, the host MUST ensure that		advertising interfaces). In addition, the host MUST ensure that
	subsequent Neighbor Advertisement messages sent from the interface		subsequent Neighbor Advertisement messages sent from the interface
	have the Router flag set to zero.		have the Router flag set to zero.
	Note that system management may disable a router's IP forwarding		Note that system management may disable a router's IP forwarding
	skipping to change at page 45, line 30		skipping to change at page 49, line 32
	Note that a router is permitted to send multicast Router		Note that a router is permitted to send multicast Router
	Advertisements more frequently than indicated by the		Advertisements more frequently than indicated by the
	MinRtrAdvInterval configuration variable so long as the more frequent		MinRtrAdvInterval configuration variable so long as the more frequent
	advertisements are responses to Router Solicitations. In all cases,		advertisements are responses to Router Solicitations. In all cases,
	however, unsolicited multicast advertisements MUST NOT be sent more		however, unsolicited multicast advertisements MUST NOT be sent more
	frequently than indicated by MinRtrAdvInterval.		frequently than indicated by MinRtrAdvInterval.
	Router Solicitations in which the Source Address is the unspecified		Router Solicitations in which the Source Address is the unspecified
	address MUST NOT update the router's Neighbor Cache; solicitations		address MUST NOT update the router's Neighbor Cache; solicitations
	with a proper source address update the Neighbor Cache as follows. If		with a proper source address update the Neighbor Cache as follows.
	the router already has a Neighbor Cache entry for the solicitation's		If the router already has a Neighbor Cache entry for the
	sender, the solicitation contains a Source Link-Layer Address option,		solicitation's sender, the solicitation contains a Source Link-Layer
	and the received link-layer address differs from that already in the		Address option, and the received link-layer address differs from that
	cache, the link-layer address SHOULD be updated in the appropriate		already in the cache, then the link-layer address SHOULD be updated
	Neighbor Cache entry, and its reachability state MUST also be set to		in the appropriate Neighbor Cache entry, and its reachability state
	STALE. If there is no existing Neighbor Cache entry for the		MUST also be set to STALE. If there is no existing Neighbor Cache
	solicitation's sender, the router creates one, installs the link-		entry for the solicitation's sender, the router creates one, installs
	layer address and sets its reachability state to STALE as specified		the link- layer address and sets its reachability state to STALE as
	in Section 7.3.3. If there is no existing Neighbor Cache entry and no		specified in Section 7.3.3. If there is no existing Neighbor Cache
	Source Link-Layer Address option was present in the solicitation, the		entry and no Source Link-Layer Address option was present in the
	router may respond with either a multicast or a unicast router		solicitation, the router may respond with either a multicast or a
	advertisement. Whether or not a Source Link-Layer Address option		unicast router advertisement. Whether or not a Source Link-Layer
	is provided, if a Neighbor Cache entry for the solicitation's sender		Address option is provided, if a Neighbor Cache entry for the
	exists (or is created) the entry's IsRouter flag MUST be set to		solicitation's sender exists (or is created) the entry's IsRouter
	FALSE.		flag MUST be set to FALSE.
	6.2.7. Router Advertisement Consistency		6.2.7. Router Advertisement Consistency
	Routers SHOULD inspect valid Router Advertisements sent by other		Routers SHOULD inspect valid Router Advertisements sent by other
	routers and verify that the routers are advertising consistent		routers and verify that the routers are advertising consistent
	information on a link. Detected inconsistencies indicate that one or		information on a link. Detected inconsistencies indicate that one or
	more routers might be misconfigured and SHOULD be logged to system or		more routers might be misconfigured and SHOULD be logged to system or
	network management. The minimum set of information to check		network management. The minimum set of information to check
	includes:		includes:
	- Cur Hop Limit values (except for the unspecified value of zero		- Cur Hop Limit values (except for the unspecified value of zero
	skipping to change at page 46, line 19		skipping to change at page 50, line 28
	- Values of the M or O flags.		- Values of the M or O flags.
	- Reachable Time values (except for the unspecified value of zero).		- Reachable Time values (except for the unspecified value of zero).
	- Retrans Timer values (except for the unspecified value of zero).		- Retrans Timer values (except for the unspecified value of zero).
	- Values in the MTU options.		- Values in the MTU options.
	- Preferred and Valid Lifetimes for the same prefix. If		- Preferred and Valid Lifetimes for the same prefix. If
	AdvPreferredLifetime and/or AdvValidLifetime decrement in real		AdvPreferredLifetime and/or AdvValidLifetime decrement in real
	time as specified in section 6.2.1 then the comparison of the		time as specified in Section 6.2.1 then the comparison of the
	lifetimes can not compare the content of the fields in the Router		lifetimes can not compare the content of the fields in the Router
	Advertisement but must instead compare the time at which the		Advertisement, but must instead compare the time at which the
	prefix will become deprecated and invalidated, respectively. Due		prefix will become deprecated and invalidated, respectively. Due
	to link propagation delays and potentially poorly synchronized		to link propagation delays and potentially poorly synchronized
	clocks between the routers such comparison SHOULD allow some time		clocks between the routers such comparison SHOULD allow some time
	skew.		skew.
	Note that it is not an error for different routers to advertise		Note that it is not an error for different routers to advertise
	different sets of prefixes. Also, some routers might leave some		different sets of prefixes. Also, some routers might leave some
	fields as unspecified, i.e., with the value zero, while other routers		fields as unspecified, i.e., with the value zero, while other routers
	specify values. The logging of errors SHOULD be restricted to		specify values. The logging of errors SHOULD be restricted to
	conflicting information that causes hosts to switch from one value to		conflicting information that causes hosts to switch from one value to
	skipping to change at page 46, line 45		skipping to change at page 51, line 5
	router is beyond the scope of this document.		router is beyond the scope of this document.
	6.2.8. Link-local Address Change		6.2.8. Link-local Address Change
	The link-local address on a router should rarely change, if ever.		The link-local address on a router should rarely change, if ever.
	Nodes receiving Neighbor Discovery messages use the source address to		Nodes receiving Neighbor Discovery messages use the source address to
	identify the sender. If multiple packets from the same router		identify the sender. If multiple packets from the same router
	contain different source addresses, nodes will assume they come from		contain different source addresses, nodes will assume they come from
	different routers, leading to undesirable behavior. For example, a		different routers, leading to undesirable behavior. For example, a
	node will ignore Redirect messages that are believed to have been		node will ignore Redirect messages that are believed to have been
	sent by a router other than the current first-hop router. Thus the		sent by a router other than the current first-hop router. Thus, the
	source address used in Router Advertisements sent by a particular		source address used in Router Advertisements sent by a particular
	router must be identical to the target address in a Redirect message		router must be identical to the target address in a Redirect message
	when redirecting to that router.		when redirecting to that router.
	Using the link-local address to uniquely identify routers on the link		Using the link-local address to uniquely identify routers on the link
	has the benefit that the address a router is known by should not		has the benefit that the address a router is known by should not
	change when a site renumbers.		change when a site renumbers.
	If a router changes the link-local address for one of its interfaces,		If a router changes the link-local address for one of its interfaces,
	it SHOULD inform hosts of this change. The router SHOULD multicast a		it SHOULD inform hosts of this change. The router SHOULD multicast a
	skipping to change at page 47, line 18		skipping to change at page 51, line 30
	interface, and a different one starts being an advertising interface.		interface, and a different one starts being an advertising interface.
	6.3. Host Specification		6.3. Host Specification
	6.3.1. Host Configuration Variables		6.3.1. Host Configuration Variables
	None.		None.
	6.3.2. Host Variables		6.3.2. Host Variables
	A host maintains certain Neighbor Discovery related variables in		A host maintains certain Neighbor-Discovery-related variables in
	addition to the data structures defined in Section 5.1. The specific		addition to the data structures defined in Section 5.1. The specific
	variable names are used for demonstration purposes only, and an		variable names are used for demonstration purposes only, and an
	implementation is not required to have them, so long as its external		implementation is not required to have them, so long as its external
	behavior is consistent with that described in this document.		behavior is consistent with that described in this document.
	These variables have default values that are overridden by		These variables have default values that are overridden by
	information received in Router Advertisement messages. The default		information received in Router Advertisement messages. The default
	values are used when there is no router on the link or when all		values are used when there is no router on the link or when all
	received Router Advertisements have left a particular value		received Router Advertisements have left a particular value
	unspecified.		unspecified.
	skipping to change at page 47, line 40		skipping to change at page 52, line 10
	The default values in this specification may be overridden by		The default values in this specification may be overridden by
	specific documents that describe how IP operates over different link		specific documents that describe how IP operates over different link
	layers. This rule allows Neighbor Discovery to operate over links		layers. This rule allows Neighbor Discovery to operate over links
	with widely varying performance characteristics.		with widely varying performance characteristics.
	For each interface:		For each interface:
	LinkMTU The MTU of the link.		LinkMTU The MTU of the link.
	Default: The valued defined in the specific		Default: The valued defined in the specific
	document that describes how IPv6 operates over		document that describes how IPv6 operates over
	the particular link-layer (e.g., [IPv6-ETHER]).		the particular link layer (e.g., [IPv6-ETHER]).
	CurHopLimit The default hop limit to be used when sending		CurHopLimit The default hop limit to be used when sending IP
	IP packets.		packets.
	Default: The value specified in the "Assigned		Default: The value specified in the "Assigned
	Numbers" RFC [ASSIGNED] that was in effect at the		Numbers" [ASSIGNED] that was in effect at the
	time of implementation.		time of implementation.
	BaseReachableTime		BaseReachableTime
	A base value used for computing the random		A base value used for computing the random
	ReachableTime value.		ReachableTime value.
	Default: REACHABLE_TIME milliseconds.		Default: REACHABLE_TIME milliseconds.
	ReachableTime The time a neighbor is considered reachable after		ReachableTime The time a neighbor is considered reachable after
	receiving a reachability confirmation.		receiving a reachability confirmation.
	This value should be a uniformly-distributed		This value should be a uniformly distributed
	random value between MIN_RANDOM_FACTOR and		random value between MIN_RANDOM_FACTOR and
	MAX_RANDOM_FACTOR times BaseReachableTime		MAX_RANDOM_FACTOR times BaseReachableTime
	milliseconds. A new random value should be		milliseconds. A new random value should be
	calculated when BaseReachableTime changes (due to		calculated when BaseReachableTime changes (due to
	Router Advertisements) or at least every few		Router Advertisements) or at least every few
	hours even if no Router Advertisements are		hours even if no Router Advertisements are
	received.		received.
	RetransTimer The time between retransmissions of Neighbor		RetransTimer The time between retransmissions of Neighbor
	Solicitation messages to a neighbor when		Solicitation messages to a neighbor when
	skipping to change at page 48, line 41		skipping to change at page 53, line 17
	When multiple routers are present, the information advertised		When multiple routers are present, the information advertised
	collectively by all routers may be a superset of the information		collectively by all routers may be a superset of the information
	contained in a single Router Advertisement. Moreover, information		contained in a single Router Advertisement. Moreover, information
	may also be obtained through other dynamic means like DHCPv6. Hosts		may also be obtained through other dynamic means like DHCPv6. Hosts
	accept the union of all received information; the receipt of a Router		accept the union of all received information; the receipt of a Router
	Advertisement MUST NOT invalidate all information received in a		Advertisement MUST NOT invalidate all information received in a
	previous advertisement or from another source. However, when		previous advertisement or from another source. However, when
	received information for a specific parameter (e.g., Link MTU) or		received information for a specific parameter (e.g., Link MTU) or
	option (e.g., Lifetime on a specific Prefix) differs from information		option (e.g., Lifetime on a specific Prefix) differs from information
	received earlier, and the parameter/option can only have one value,		received earlier, and the parameter/option can only have one value,
	the most recently-received information is considered authoritative.		the most recently received information is considered authoritative.
	Some Router Advertisement fields (e.g., Cur Hop Limit, Reachable Time		A Router Advertisement field (e.g., Cur Hop Limit, Reachable Time,
	and Retrans Timer) may contain a value denoting unspecified. In such		and Retrans Timer) may contain a value denoting that it is
	cases, the parameter should be ignored and the host should continue		unspecified. In such cases, the parameter should be ignored and the
	using whatever value it is already using. In particular, a host MUST		host should continue using whatever value it is already using. In
	NOT interpret the unspecified value as meaning change back to the		particular, a host MUST NOT interpret the unspecified value as
	default value that was in use before the first Router Advertisement		meaning change back to the default value that was in use before the
	was received. This rule prevents hosts from continually changing an		first Router Advertisement was received. This rule prevents hosts
	internal variable when one router advertises a specific value, but		from continually changing an internal variable when one router
	other routers advertise the unspecified value.		advertises a specific value, but other routers advertise the
			unspecified value.
	On receipt of a valid Router Advertisement, a host extracts the		On receipt of a valid Router Advertisement, a host extracts the
	source address of the packet and does the following:		source address of the packet and does the following:
	- If the address is not already present in the host's Default		- If the address is not already present in the host's Default
	Router List, and the advertisement's Router Lifetime is non-		Router List, and the advertisement's Router Lifetime is non-
	zero, create a new entry in the list, and initialize its		zero, create a new entry in the list, and initialize its
	invalidation timer value from the advertisement's Router		invalidation timer value from the advertisement's Router
	Lifetime field.		Lifetime field.
	- If the address is already present in the host's Default Router		- If the address is already present in the host's Default Router
	List as a result of a previously-received advertisement, reset		List as a result of a previously received advertisement, reset
	its invalidation timer to the Router Lifetime value in the		its invalidation timer to the Router Lifetime value in the newly
	newly-received advertisement.		received advertisement.
	- If the address is already present in the host's Default Router		- If the address is already present in the host's Default Router
	List and the received Router Lifetime value is zero, immediately		List and the received Router Lifetime value is zero, immediately
	time-out the entry as specified in Section 6.3.5.		time-out the entry as specified in Section 6.3.5.
	To limit the storage needed for the Default Router List, a host MAY		To limit the storage needed for the Default Router List, a host MAY
	choose not to store all of the router addresses discovered via		choose not to store all of the router addresses discovered via
	advertisements. However, a host MUST retain at least two router		advertisements. However, a host MUST retain at least two router
	addresses and SHOULD retain more. Default router selections are made		addresses and SHOULD retain more. Default router selections are made
	whenever communication to a destination appears to be failing. Thus,		whenever communication to a destination appears to be failing. Thus,
	the more routers on the list, the more likely an alternative working		the more routers on the list, the more likely an alternative working
	router can be found quickly (e.g., without having to wait for the		router can be found quickly (e.g., without having to wait for the
	next advertisement to arrive).		next advertisement to arrive).
	If the received Cur Hop Limit value is non-zero the host SHOULD set		If the received Cur Hop Limit value is non-zero, the host SHOULD set
	its CurHopLimit variable to the received value.		its CurHopLimit variable to the received value.
	If the received Reachable Time value is non-zero the host SHOULD set		If the received Reachable Time value is non-zero, the host SHOULD set
	its BaseReachableTime variable to the received value. If the new		its BaseReachableTime variable to the received value. If the new
	value differs from the previous value, the host SHOULD recompute a		value differs from the previous value, the host SHOULD re-compute a
	new random ReachableTime value. ReachableTime is computed as a		new random ReachableTime value. ReachableTime is computed as a
	uniformly-distributed random value between MIN_RANDOM_FACTOR and		uniformly distributed random value between MIN_RANDOM_FACTOR and
	MAX_RANDOM_FACTOR times the BaseReachableTime. Using a random		MAX_RANDOM_FACTOR times the BaseReachableTime. Using a random
	component eliminates the possibility Neighbor Unreachability		component eliminates the possibility that Neighbor Unreachability
	Detection messages synchronize with each other.		Detection messages will synchronize with each other.
	In most cases, the advertised Reachable Time value will be the same		In most cases, the advertised Reachable Time value will be the same
	in consecutive Router Advertisements and a host's BaseReachableTime		in consecutive Router Advertisements, and a host's BaseReachableTime
	rarely changes. In such cases, an implementation SHOULD insure that		rarely changes. In such cases, an implementation SHOULD ensure that
	a new random value gets recomputed at least once every few hours.		a new random value gets re-computed at least once every few hours.
	The RetransTimer variable SHOULD be copied from the Retrans Timer		The RetransTimer variable SHOULD be copied from the Retrans Timer
	field, if the received value is non-zero.		field, if the received value is non-zero.
	After extracting information from the fixed part of the Router		After extracting information from the fixed part of the Router
	Advertisement message, the advertisement is scanned for valid		Advertisement message, the advertisement is scanned for valid
	options. If the advertisement contains a Source Link-Layer Address		options. If the advertisement contains a Source Link-Layer Address
	option the link-layer address SHOULD be recorded in the Neighbor		option, the link-layer address SHOULD be recorded in the Neighbor
	Cache entry for the router (creating an entry if necessary) and the		Cache entry for the router (creating an entry if necessary) and the
	IsRouter flag in the Neighbor Cache entry MUST be set to TRUE. If no		IsRouter flag in the Neighbor Cache entry MUST be set to TRUE. If no
	Source Link-Layer Address is included, but a corresponding Neighbor		Source Link-Layer Address is included, but a corresponding Neighbor
	Cache entry exists, its IsRouter flag MUST be set to TRUE. The		Cache entry exists, its IsRouter flag MUST be set to TRUE. The
	IsRouter flag is used by Neighbor Unreachability Detection to		IsRouter flag is used by Neighbor Unreachability Detection to
	determine when a router changes to being a host (i.e., no longer		determine when a router changes to being a host (i.e., no longer
	capable of forwarding packets). If a Neighbor Cache entry is created		capable of forwarding packets). If a Neighbor Cache entry is created
	for the router its reachability state MUST be set to STALE as		for the router, its reachability state MUST be set to STALE as
	specified in Section 7.3.3. If a cache entry already exists and is		specified in Section 7.3.3. If a cache entry already exists and is
	updated with a different link-layer address the reachability state		updated with a different link-layer address, the reachability state
	MUST also be set to STALE.		MUST also be set to STALE.
	If the MTU option is present, hosts SHOULD copy the option's value		If the MTU option is present, hosts SHOULD copy the option's value
	into LinkMTU so long as the value is greater than or equal to the		into LinkMTU so long as the value is greater than or equal to the
	minimum link MTU [IPv6] and does not exceed the maximum LinkMTU value		minimum link MTU [IPv6] and does not exceed the maximum LinkMTU value
	specified in the link type specific document (e.g., [IPv6-ETHER]).		specified in the link-type-specific document (e.g., [IPv6-ETHER]).
	Prefix Information options that have the "on-link" (L) flag set		Prefix Information options that have the "on-link" (L) flag set
	indicate a prefix identifying a range of addresses that should be		indicate a prefix identifying a range of addresses that should be
	considered on-link. Note, however, that a Prefix Information option		considered on-link. Note, however, that a Prefix Information option
	with the on-link flag set to zero conveys no information concerning		with the on-link flag set to zero conveys no information concerning
	on-link determination and MUST NOT be interpreted to mean that		on-link determination and MUST NOT be interpreted to mean that
	addresses covered by the prefix are off-link. The only way to cancel		addresses covered by the prefix are off-link. The only way to cancel
	a previous on-link indication is to advertise that prefix with the		a previous on-link indication is to advertise that prefix with the
	L-bit set and the Lifetime set to zero. The default behavior (see		L-bit set and the Lifetime set to zero. The default behavior (see
	Section 5.2) when sending a packet to an address for which no		Section 5.2) when sending a packet to an address for which no
	skipping to change at page 50, line 48		skipping to change at page 55, line 31
	- If the prefix is the link-local prefix, silently ignore the		- If the prefix is the link-local prefix, silently ignore the
	Prefix Information option.		Prefix Information option.
	- If the prefix is not already present in the Prefix List, and the		- If the prefix is not already present in the Prefix List, and the
	Prefix Information option's Valid Lifetime field is non-zero,		Prefix Information option's Valid Lifetime field is non-zero,
	create a new entry for the prefix and initialize its		create a new entry for the prefix and initialize its
	invalidation timer to the Valid Lifetime value in the Prefix		invalidation timer to the Valid Lifetime value in the Prefix
	Information option.		Information option.
	- If the prefix is already present in the host's Prefix List as		- If the prefix is already present in the host's Prefix List as
	the result of a previously-received advertisement, reset its		the result of a previously received advertisement, reset its
	invalidation timer to the Valid Lifetime value in the Prefix		invalidation timer to the Valid Lifetime value in the Prefix
	Information option. If the new Lifetime value is zero, time-out		Information option. If the new Lifetime value is zero, time-out
	the prefix immediately (see Section 6.3.5).		the prefix immediately (see Section 6.3.5).
	- If the Prefix Information option's Valid Lifetime field is zero,		- If the Prefix Information option's Valid Lifetime field is zero,
	and the prefix is not present in the host's Prefix List,		and the prefix is not present in the host's Prefix List,
	silently ignore the option.		silently ignore the option.
	Stateless address autoconfiguration [ADDRCONF] may in some		Stateless address autoconfiguration [ADDRCONF] may in some
	circumstances use a larger Valid Lifetime of a prefix or ignore it		circumstances use a larger Valid Lifetime of a prefix or ignore it
	completely in order to prevent a particular denial of service attack.		completely in order to prevent a particular denial-of-service attack.
	However, since the effect of the same denial of service targeted at		However, since the effect of the same denial of service targeted at
	the on-link prefix list is not catastrophic (hosts would send packets		the on-link prefix list is not catastrophic (hosts would send packets
	to a default router and receive a redirect rather than sending		to a default router and receive a redirect rather than sending
	packets directly to a neighbor) the Neighbor Discovery protocol does		packets directly to a neighbor), the Neighbor Discovery protocol does
	not impose such a check on the prefix lifetime values. Similarly,		not impose such a check on the prefix lifetime values. Similarly,
	[ADDRCONF] may impose certain restrictions on the prefix length for		[ADDRCONF] may impose certain restrictions on the prefix length for
	address configuration purposes. Therefore, the prefix might be		address configuration purposes. Therefore, the prefix might be
	rejected by [ADDRCONF] implementation in the host. However, the		rejected by [ADDRCONF] implementation in the host. However, the
	prefix length is still valid for on-link determination when combined		prefix length is still valid for on-link determination when combined
	with other flags in the prefix option.		with other flags in the prefix option.
	Note: Implementations can choose to process the on-link aspects of		Note: Implementations can choose to process the on-link aspects of
	the prefixes separately from the stateless address		the prefixes separately from the stateless address
	autoconfiguration aspects of the prefixes by, e.g., passing a copy		autoconfiguration aspects of the prefixes by, e.g., passing a copy
	skipping to change at page 52, line 35		skipping to change at page 57, line 24
	router is made in conjunction with the sending of a packet to a		router is made in conjunction with the sending of a packet to a
	router, and the selected router will be probed for reachability		router, and the selected router will be probed for reachability
	as a side effect.		as a side effect.
	6.3.7. Sending Router Solicitations		6.3.7. Sending Router Solicitations
	When an interface becomes enabled, a host may be unwilling to wait		When an interface becomes enabled, a host may be unwilling to wait
	for the next unsolicited Router Advertisement to locate default		for the next unsolicited Router Advertisement to locate default
	routers or learn prefixes. To obtain Router Advertisements quickly,		routers or learn prefixes. To obtain Router Advertisements quickly,
	a host SHOULD transmit up to MAX_RTR_SOLICITATIONS Router		a host SHOULD transmit up to MAX_RTR_SOLICITATIONS Router
	Solicitation messages each separated by at least		Solicitation messages, each separated by at least
	RTR_SOLICITATION_INTERVAL seconds. Router Solicitations may be sent		RTR_SOLICITATION_INTERVAL seconds. Router Solicitations may be sent
	after any of the following events:		after any of the following events:
	- The interface is initialized at system startup time.		- The interface is initialized at system startup time.
	- The interface is reinitialized after a temporary interface		- The interface is reinitialized after a temporary interface
	failure or after being temporarily disabled by system		failure or after being temporarily disabled by system
	management.		management.
	- The system changes from being a router to being a host, by		- The system changes from being a router to being a host, by
	having its IP forwarding capability turned off by system		having its IP forwarding capability turned off by system
	management.		management.
	- The host attaches to a link for the first time.		- The host attaches to a link for the first time.
	- The host re-attaches to a link after being detached for some		- The host re-attaches to a link after being detached for some
	time.		time.
	A host sends Router Solicitations to the All-Routers multicast		A host sends Router Solicitations to the all-routers multicast
	address. The IP source address is set to either one of the		address. The IP source address is set to either one of the
	interface's unicast addresses or the unspecified address. The Source		interface's unicast addresses or the unspecified address. The Source
	Link-Layer Address option SHOULD be set to the host's link-layer		Link-Layer Address option SHOULD be set to the host's link-layer
	address, if the IP source address is not the unspecified address.		address, if the IP source address is not the unspecified address.
	Before a host sends an initial solicitation, it SHOULD delay the		Before a host sends an initial solicitation, it SHOULD delay the
	transmission for a random amount of time between 0 and		transmission for a random amount of time between 0 and
	MAX_RTR_SOLICITATION_DELAY. This serves to alleviate congestion when		MAX_RTR_SOLICITATION_DELAY. This serves to alleviate congestion when
	many hosts start up on a link at the same time, such as might happen		many hosts start up on a link at the same time, such as might happen
	after recovery from a power failure. If a host has already performed		after recovery from a power failure. If a host has already performed
	a random delay since the interface became (re)enabled (e.g., as part		a random delay since the interface became (re)enabled (e.g., as part
	of Duplicate Address Detection [ADDRCONF]) there is no need to delay		of Duplicate Address Detection [ADDRCONF]), there is no need to delay
	again before sending the first Router Solicitation message.		again before sending the first Router Solicitation message.
	In some cases, the random delay MAY be omitted if necessary. For		In some cases, the random delay MAY be omitted if necessary. For
	instance, a mobile node, using [MIPv6], moving to a new link would		instance, a mobile node, using [MIPv6], moving to a new link would
	need to discover such movement as soon as possible to minimize the		need to discover such movement as soon as possible to minimize the
	amount of packet losses resulting from the change in its topological		amount of packet losses resulting from the change in its topological
	movement. Router Solicitations provide a useful tool for movement		movement. Router Solicitations provide a useful tool for movement
	detection in Mobile IPv6 as they allow mobile nodes to determine		detection in Mobile IPv6 as they allow mobile nodes to determine
	movement to new links. Hence, if a mobile node received link-layer		movement to new links. Hence, if a mobile node received link-layer
	information indicating that movement might have taken place, it MAY		information indicating that movement might have taken place, it MAY
	send a Router Solicitation immediately, without random delays. The		send a Router Solicitation immediately, without random delays. The
	strength of such indications should be assessed by the mobile node's		strength of such indications should be assessed by the mobile node's
	implementation depending on the level of certainty of the link-layer		implementation depending on the level of certainty of the link-layer
	hints and is outside the scope of this specification. Note that using		hints, and it is outside the scope of this specification. Note that
	this mechanism inappropriately (e.g. based on weak or transient		using this mechanism inappropriately (e.g., based on weak or
	indications) may result in Router Solicitation storms. Furthermore,		transient indications) may result in Router Solicitation storms.
	simultaneous mobility of a large number of mobile nodes that use this		Furthermore, simultaneous mobility of a large number of mobile nodes
	mechanism can result in a large number of solicitations sent		that use this mechanism can result in a large number of solicitations
	simultaneously.		sent simultaneously.
	Once the host sends a Router Solicitation, and receives a valid		Once the host sends a Router Solicitation, and receives a valid
	Router Advertisement with a non-zero Router Lifetime, the host MUST		Router Advertisement with a non-zero Router Lifetime, the host MUST
	desist from sending additional solicitations on that interface, until		desist from sending additional solicitations on that interface, until
	the next time one of the above events occurs. Moreover, a host		the next time one of the above events occurs. Moreover, a host
	SHOULD send at least one solicitation in the case where an		SHOULD send at least one solicitation in the case where an
	advertisement is received prior to having sent a solicitation.		advertisement is received prior to having sent a solicitation.
	Responses to solicited advertisements are expected to contain		Responses to solicited advertisements may contain more information
	complete information.		than unsolicited advertisements.
	If a host sends MAX_RTR_SOLICITATIONS solicitations, and receives no		If a host sends MAX_RTR_SOLICITATIONS solicitations, and receives no
	Router Advertisements after having waited MAX_RTR_SOLICITATION_DELAY		Router Advertisements after having waited MAX_RTR_SOLICITATION_DELAY
	seconds after sending the last solicitation, the host concludes that		seconds after sending the last solicitation, the host concludes that
	there are no routers on the link for the purpose of [ADDRCONF].		there are no routers on the link for the purpose of [ADDRCONF].
	However, the host continues to receive and process Router		However, the host continues to receive and process Router
	Advertisements messages in the event that routers appear on the link.		Advertisements messages in the event that routers appear on the link.
	7. ADDRESS RESOLUTION AND NEIGHBOR UNREACHABILITY DETECTION		7. Address Resolution and Neighbor Unreachability Detection
	This section describes the functions related to Neighbor Solicitation		This section describes the functions related to Neighbor Solicitation
	and Neighbor Advertisement messages and includes descriptions of		and Neighbor Advertisement messages and includes descriptions of
	address resolution and the Neighbor Unreachability Detection		address resolution and the Neighbor Unreachability Detection
	algorithm.		algorithm.
	Neighbor Solicitation and Advertisement messages are also used for		Neighbor Solicitation and Advertisement messages are also used for
	Duplicate Address Detection as specified by [ADDRCONF]. In		Duplicate Address Detection as specified by [ADDRCONF]. In
	particular, Duplicate Address Detection sends Neighbor Solicitation		particular, Duplicate Address Detection sends Neighbor Solicitation
	messages with an unspecified source address targeting its own		messages with an unspecified source address targeting its own
	"tentative" address. Such messages trigger nodes already using the		"tentative" address. Such messages trigger nodes already using the
	skipping to change at page 55, line 45		skipping to change at page 61, line 4
	A Neighbor Advertisements that passes the validity checks is called a		A Neighbor Advertisements that passes the validity checks is called a
	"valid advertisement".		"valid advertisement".
	7.2. Address Resolution		7.2. Address Resolution
	Address resolution is the process through which a node determines the		Address resolution is the process through which a node determines the
	link-layer address of a neighbor given only its IP address. Address		link-layer address of a neighbor given only its IP address. Address
	resolution is performed only on addresses that are determined to be		resolution is performed only on addresses that are determined to be
	on-link and for which the sender does not know the corresponding		on-link and for which the sender does not know the corresponding
	link-layer address (see section 5.2). Address resolution is never		link-layer address (see Section 5.2). Address resolution is never
	performed on multicast addresses.		performed on multicast addresses.
	It is possible that a host may receive a solicitation, a router		It is possible that a host may receive a solicitation, a router
	advertisement, or a Redirect message without a link-layer address		advertisement, or a Redirect message without a link-layer address
	option included. These messages MUST NOT create or update neighbor		option included. These messages MUST NOT create or update neighbor
	cache entries, except with respect to the IsRouter flag as specified		cache entries, except with respect to the IsRouter flag as specified
	in sections 6.3.4 and 7.2.5. If a neighbor cache entry does not exist		in Sections 6.3.4 and 7.2.5. If a Neighbor Cache entry does not
	for the source of such a message, Address Resolution will be required		exist for the source of such a message, Address Resolution will be
	before unicast communications with that address can begin. This is		required before unicast communications with that address can begin.
	particularly relevant for unicast responses to solicitations where an		This is particularly relevant for unicast responses to solicitations
	additional packet exchange is required for advertisement delivery.		where an additional packet exchange is required for advertisement
			delivery.
	7.2.1. Interface Initialization		7.2.1. Interface Initialization
	When a multicast-capable interface becomes enabled the node MUST join		When a multicast-capable interface becomes enabled, the node MUST
	the all-nodes multicast address on that interface, as well as the		join the all-nodes multicast address on that interface, as well as
	solicited-node multicast address corresponding to each of the IP		the solicited-node multicast address corresponding to each of the IP
	addresses assigned to the interface.		addresses assigned to the interface.
	The set of addresses assigned to an interface may change over time.		The set of addresses assigned to an interface may change over time.
	New addresses might be added and old addresses might be removed		New addresses might be added and old addresses might be removed
	[ADDRCONF]. In such cases the node MUST join and leave the		[ADDRCONF]. In such cases the node MUST join and leave the
	solicited-node multicast address corresponding to the new and old		solicited-node multicast address corresponding to the new and old
	addresses, respectively. Joining the solicited-node multicast address		addresses, respectively. Joining the solicited-node multicast
	is done using a Multicast Listener Discovery such as [MLD] or [MLDv2]		address is done using a Multicast Listener Discovery such as [MLD] or
	protocols. Note that multiple unicast addresses may map into the same		[MLDv2] protocols. Note that multiple unicast addresses may map into
	solicited-node multicast address; a node MUST NOT leave the		the same solicited-node multicast address; a node MUST NOT leave the
	solicited-node multicast group until all assigned addresses		solicited-node multicast group until all assigned addresses
	corresponding to that multicast address have been removed.		corresponding to that multicast address have been removed.
	7.2.2. Sending Neighbor Solicitations		7.2.2. Sending Neighbor Solicitations
	When a node has a unicast packet to send to a neighbor, but does not		When a node has a unicast packet to send to a neighbor, but does not
	know the neighbor's link-layer address, it performs address		know the neighbor's link-layer address, it performs address
	resolution. For multicast-capable interfaces this entails creating a		resolution. For multicast-capable interfaces, this entails creating
	Neighbor Cache entry in the INCOMPLETE state and transmitting a		a Neighbor Cache entry in the INCOMPLETE state and transmitting a
	Neighbor Solicitation message targeted at the neighbor. The		Neighbor Solicitation message targeted at the neighbor. The
	solicitation is sent to the solicited-node multicast address		solicitation is sent to the solicited-node multicast address
	corresponding to the target address.		corresponding to the target address.
	If the source address of the packet prompting the solicitation is the		If the source address of the packet prompting the solicitation is the
	same as one of the addresses assigned to the outgoing interface, that		same as one of the addresses assigned to the outgoing interface, that
	address SHOULD be placed in the IP Source Address of the outgoing		address SHOULD be placed in the IP Source Address of the outgoing
	solicitation. Otherwise, any one of the addresses assigned to the		solicitation. Otherwise, any one of the addresses assigned to the
	interface should be used. Using the prompting packet's source		interface should be used. Using the prompting packet's source
	address when possible ensures that the recipient of the Neighbor		address when possible ensures that the recipient of the Neighbor
	skipping to change at page 57, line 36		skipping to change at page 63, line 4
	7.2.3. Receipt of Neighbor Solicitations		7.2.3. Receipt of Neighbor Solicitations
	A valid Neighbor Solicitation that does not meet any of the following		A valid Neighbor Solicitation that does not meet any of the following
	requirements MUST be silently discarded:		requirements MUST be silently discarded:
	- The Target Address is a "valid" unicast or anycast address		- The Target Address is a "valid" unicast or anycast address
	assigned to the receiving interface [ADDRCONF],		assigned to the receiving interface [ADDRCONF],
	- The Target Address is a unicast or anycast address for which the		- The Target Address is a unicast or anycast address for which the
	node is offering proxy service, or		node is offering proxy service, or
	- The Target Address is a "tentative" address on which Duplicate		- The Target Address is a "tentative" address on which Duplicate
	Address Detection is being performed [ADDRCONF].		Address Detection is being performed [ADDRCONF].
	If the Target Address is tentative, the Neighbor Solicitation should		If the Target Address is tentative, the Neighbor Solicitation should
	be processed as described in [ADDRCONF]. Otherwise, the following		be processed as described in [ADDRCONF]. Otherwise, the following
	description applies. If the Source Address is not the unspecified		description applies. If the Source Address is not the unspecified
	address and, on link-layers that have addresses, the solicitation		address and, on link layers that have addresses, the solicitation
	includes a Source Link-Layer Address option, then the recipient		includes a Source Link-Layer Address option, then the recipient
	SHOULD create or update the Neighbor Cache entry for the IP Source		SHOULD create or update the Neighbor Cache entry for the IP Source
	Address of the solicitation. If an entry does not already exist, the		Address of the solicitation. If an entry does not already exist, the
	node SHOULD create a new one and set its reachability state to STALE		node SHOULD create a new one and set its reachability state to STALE
	as specified in Section 7.3.3. If an entry already exists, and the		as specified in Section 7.3.3. If an entry already exists, and the
	cached link-layer address differs from the one in the received Source		cached link-layer address differs from the one in the received Source
	Link-Layer option, the cached address should be replaced by the		Link-Layer option, the cached address should be replaced by the
	received address and the entry's reachability state MUST be set to		received address, and the entry's reachability state MUST be set to
	STALE.		STALE.
	If a Neighbor Cache entry is created the IsRouter flag SHOULD be set		If a Neighbor Cache entry is created, the IsRouter flag SHOULD be set
	to FALSE. This will be the case even if the Neighbor Solicitation is		to FALSE. This will be the case even if the Neighbor Solicitation is
	sent by a router since the Neighbor Solicitation messages do not		sent by a router since the Neighbor Solicitation messages do not
	contain an indication of whether or not the sender is a router. In		contain an indication of whether or not the sender is a router. In
	the event that the sender is a router, subsequent Neighbor		the event that the sender is a router, subsequent Neighbor
	Advertisement or Router Advertisement messages will set the correct		Advertisement or Router Advertisement messages will set the correct
	IsRouter value. If a Neighbor Cache entry already exists its		IsRouter value. If a Neighbor Cache entry already exists, its
	IsRouter flag MUST NOT be modified.		IsRouter flag MUST NOT be modified.
	If the Source Address is the unspecified address the node MUST NOT		If the Source Address is the unspecified address, the node MUST NOT
	create or update the Neighbor Cache entry.		create or update the Neighbor Cache entry.
	After any updates to the Neighbor Cache, the node sends a Neighbor		After any updates to the Neighbor Cache, the node sends a Neighbor
	Advertisement response as described in the next section.		Advertisement response as described in the next section.
	7.2.4. Sending Solicited Neighbor Advertisements		7.2.4. Sending Solicited Neighbor Advertisements
	A node sends a Neighbor Advertisement in response to a valid Neighbor		A node sends a Neighbor Advertisement in response to a valid Neighbor
	Solicitation targeting one of the node's assigned addresses. The		Solicitation targeting one of the node's assigned addresses. The
	Target Address of the advertisement is copied from the Target Address		Target Address of the advertisement is copied from the Target Address
	of the solicitation. If the solicitation's IP Destination Address is		of the solicitation. If the solicitation's IP Destination Address is
	not a multicast address, the Target Link-Layer Address option MAY be		not a multicast address, the Target Link-Layer Address option MAY be
	omitted; the neighboring node's cached value must already be current		omitted; the neighboring node's cached value must already be current
	in order for the solicitation to have been received. If the		in order for the solicitation to have been received. If the
	solicitation's IP Destination Address is a multicast address, the		solicitation's IP Destination Address is a multicast address, the
	Target Link-Layer option MUST be included in the advertisement.		Target Link-Layer option MUST be included in the advertisement.
	Furthermore, if the node is a router, it MUST set the Router flag to		Furthermore, if the node is a router, it MUST set the Router flag to
	one; otherwise it MUST set the flag to zero.		one; otherwise, it MUST set the flag to zero.
	If the Target Address is either an anycast address or a unicast		If the Target Address is either an anycast address or a unicast
	address for which the node is providing proxy service, or the Target		address for which the node is providing proxy service, or the Target
	Link-Layer Address option is not included, the Override flag SHOULD		Link-Layer Address option is not included, the Override flag SHOULD
	be set to zero. Otherwise, the Override flag SHOULD be set to one.		be set to zero. Otherwise, the Override flag SHOULD be set to one.
	Proper setting of the Override flag ensures that nodes give		Proper setting of the Override flag ensures that nodes give
	preference to non-proxy advertisements, even when received after		preference to non-proxy advertisements, even when received after
	proxy advertisements, and also ensures that the first advertisement		proxy advertisements, and also ensures that the first advertisement
	for an anycast address "wins".		for an anycast address "wins".
	If the source of the solicitation is the unspecified address, the		If the source of the solicitation is the unspecified address, the
	node MUST set the Solicited flag to zero and multicast the		node MUST set the Solicited flag to zero and multicast the
	advertisement to the all-nodes address. Otherwise, the node MUST set		advertisement to the all-nodes address. Otherwise, the node MUST set
	the Solicited flag to one and unicast the advertisement to the Source		the Solicited flag to one and unicast the advertisement to the Source
	Address of the solicitation.		Address of the solicitation.
	If the Target Address is an anycast address the sender SHOULD delay		If the Target Address is an anycast address, the sender SHOULD delay
	sending a response for a random time between 0 and		sending a response for a random time between 0 and
	MAX_ANYCAST_DELAY_TIME seconds.		MAX_ANYCAST_DELAY_TIME seconds.
	Because unicast Neighbor Solicitations are not required to include a		Because unicast Neighbor Solicitations are not required to include a
	Source Link-Layer Address, it is possible that a node sending a		Source Link-Layer Address, it is possible that a node sending a
	solicited Neighbor Advertisement does not have a corresponding link-		solicited Neighbor Advertisement does not have a corresponding link-
	layer address for its neighbor in its Neighbor Cache. In such		layer address for its neighbor in its Neighbor Cache. In such
	situations, a node will first have to use Neighbor Discovery to		situations, a node will first have to use Neighbor Discovery to
	determine the link-layer address of its neighbor (i.e., send out a		determine the link-layer address of its neighbor (i.e., send out a
	multicast Neighbor Solicitation).		multicast Neighbor Solicitation).
	skipping to change at page 59, line 19		skipping to change at page 64, line 43
	When a valid Neighbor Advertisement is received (either solicited or		When a valid Neighbor Advertisement is received (either solicited or
	unsolicited), the Neighbor Cache is searched for the target's entry.		unsolicited), the Neighbor Cache is searched for the target's entry.
	If no entry exists, the advertisement SHOULD be silently discarded.		If no entry exists, the advertisement SHOULD be silently discarded.
	There is no need to create an entry if none exists, since the		There is no need to create an entry if none exists, since the
	recipient has apparently not initiated any communication with the		recipient has apparently not initiated any communication with the
	target.		target.
	Once the appropriate Neighbor Cache entry has been located, the		Once the appropriate Neighbor Cache entry has been located, the
	specific actions taken depend on the state of the Neighbor Cache		specific actions taken depend on the state of the Neighbor Cache
	entry, the flags in the advertisement and the actual link-layer		entry, the flags in the advertisement, and the actual link-layer
	address supplied.		address supplied.
	If the target's Neighbor Cache entry is in the INCOMPLETE state when		If the target's Neighbor Cache entry is in the INCOMPLETE state when
	the advertisement is received, one of two things happens. If the		the advertisement is received, one of two things happens. If the
	link-layer has addresses and no Target Link-Layer address option is		link layer has addresses and no Target Link-Layer Address option is
	included, the receiving node SHOULD silently discard the received		included, the receiving node SHOULD silently discard the received
	advertisement. Otherwise, the receiving node performs the following		advertisement. Otherwise, the receiving node performs the following
	steps:		steps:
	- It records the link-layer address in the Neighbor Cache entry.		- It records the link-layer address in the Neighbor Cache entry.
	- If the advertisement's Solicited flag is set, the state of the		- If the advertisement's Solicited flag is set, the state of the
	entry is set to REACHABLE, otherwise it is set to STALE.		entry is set to REACHABLE; otherwise, it is set to STALE.
	- It sets the IsRouter flag in the cache entry based on the Router		- It sets the IsRouter flag in the cache entry based on the Router
	flag in the received advertisement.		flag in the received advertisement.
	- It sends any packets queued for the neighbor awaiting address		- It sends any packets queued for the neighbor awaiting address
	resolution.		resolution.
	Note that the Override flag is ignored if the entry is in the		Note that the Override flag is ignored if the entry is in the
	INCOMPLETE state.		INCOMPLETE state.
	skipping to change at page 60, line 6		skipping to change at page 65, line 32
	I. If the Override flag is clear and the supplied link-layer address		I. If the Override flag is clear and the supplied link-layer address
	differs from that in the cache, then one of two actions takes		differs from that in the cache, then one of two actions takes
	place:		place:
	a. If the state of the entry is REACHABLE, set it to STALE, but		a. If the state of the entry is REACHABLE, set it to STALE, but
	do not update the entry in any other way.		do not update the entry in any other way.
	b. Otherwise, the received advertisement should be ignored and		b. Otherwise, the received advertisement should be ignored and
	MUST NOT update the cache.		MUST NOT update the cache.
	II. If the Override flag is set, or the supplied link-layer address		II. If the Override flag is set, or the supplied link-layer address
	is the same as that in the cache, or no Target Link-layer address		is the same as that in the cache, or no Target Link-Layer Address
	option was supplied, the received advertisement MUST update the		option was supplied, the received advertisement MUST update the
	Neighbor Cache entry as follows:		Neighbor Cache entry as follows:
	- The link-layer address in the Target Link-Layer Address option		- The link-layer address in the Target Link-Layer Address option
	MUST be inserted in the cache (if one is supplied and differs		MUST be inserted in the cache (if one is supplied and differs
	from the already recorded address).		from the already recorded address).
	- If the Solicited flag is set, the state of the entry MUST be		- If the Solicited flag is set, the state of the entry MUST be
	set to REACHABLE. If the Solicited flag is zero and the link		set to REACHABLE. If the Solicited flag is zero and the link-
	layer address was updated with a different address the state		layer address was updated with a different address, the state
	MUST be set to STALE. Otherwise, the entry's state remains		MUST be set to STALE. Otherwise, the entry's state remains
	unchanged.		unchanged.
	An advertisement's Solicited flag should only be set if the		An advertisement's Solicited flag should only be set if the
	advertisement is a response to a Neighbor Solicitation.		advertisement is a response to a Neighbor Solicitation.
	Because Neighbor Unreachability Detection Solicitations are		Because Neighbor Unreachability Detection Solicitations are
	sent to the cached link-layer address, receipt of a solicited		sent to the cached link-layer address, receipt of a solicited
	advertisement indicates that the forward path is working.		advertisement indicates that the forward path is working.
	Receipt of an unsolicited advertisement, however, may indicate		Receipt of an unsolicited advertisement, however, may indicate
	that a neighbor has urgent information to announce (e.g., a		that a neighbor has urgent information to announce (e.g., a
	changed link-layer address). If the urgent information		changed link-layer address). If the urgent information
	indicates a change from what a node is currently using, the		indicates a change from what a node is currently using, the
	node should verify the reachability of the (new) path when it		node should verify the reachability of the (new) path when it
	sends the next packet. There is no need to update the state for		sends the next packet. There is no need to update the state
	unsolicited advertisements that do not change the contents of		for unsolicited advertisements that do not change the contents
	the cache.		of the cache.
	- The IsRouter flag in the cache entry MUST be set based on the		- The IsRouter flag in the cache entry MUST be set based on the
	Router flag in the received advertisement. In those cases		Router flag in the received advertisement. In those cases
	where the IsRouter flag changes from TRUE to FALSE as a result		where the IsRouter flag changes from TRUE to FALSE as a result
	of this update, the node MUST remove that router from the		of this update, the node MUST remove that router from the
	Default Router List and update the Destination Cache entries		Default Router List and update the Destination Cache entries
	for all destinations using that neighbor as a router as		for all destinations using that neighbor as a router as
	specified in Section 7.3.3. This is needed to detect when a		specified in Section 7.3.3. This is needed to detect when a
	node that is used as a router stops forwarding packets due to		node that is used as a router stops forwarding packets due to
	being configured as a host.		being configured as a host.
	The above rules ensure that the cache is updated either when the		The above rules ensure that the cache is updated either when the
	Neighbor Advertisement takes precedence (i.e., the Override flag is		Neighbor Advertisement takes precedence (i.e., the Override flag is
	set) or when the Neighbor Advertisement refers to the same link-layer		set) or when the Neighbor Advertisement refers to the same link-layer
	address that is currently recorded in the cache. If none of the		address that is currently recorded in the cache. If none of the
	above apply, the advertisement prompts future Neighbor Unreachability		above apply, the advertisement prompts future Neighbor Unreachability
	Detection (if it is not already in progress) by changing the state in		Detection (if it is not already in progress) by changing the state in
	the cache entry.		the cache entry.
	7.2.6. Sending Unsolicited Neighbor Advertisements		7.2.6. Sending Unsolicited Neighbor Advertisements
	In some cases a node may be able to determine that its link-layer
			In some cases, a node may be able to determine that its link-layer
	address has changed (e.g., hot-swap of an interface card) and may		address has changed (e.g., hot-swap of an interface card) and may
	wish to inform its neighbors of the new link-layer address quickly.		wish to inform its neighbors of the new link-layer address quickly.
	In such cases a node MAY send up to MAX_NEIGHBOR_ADVERTISEMENT		In such cases, a node MAY send up to MAX_NEIGHBOR_ADVERTISEMENT
	unsolicited Neighbor Advertisement messages to the all-nodes		unsolicited Neighbor Advertisement messages to the all-nodes
	multicast address. These advertisements MUST be separated by at		multicast address. These advertisements MUST be separated by at
	least RetransTimer seconds.		least RetransTimer seconds.
	The Target Address field in the unsolicited advertisement is set to		The Target Address field in the unsolicited advertisement is set to
	an IP address of the interface, and the Target Link-Layer Address		an IP address of the interface, and the Target Link-Layer Address
	option is filled with the new link-layer address. The Solicited flag		option is filled with the new link-layer address. The Solicited flag
	MUST be set to zero, in order to avoid confusing the Neighbor		MUST be set to zero, in order to avoid confusing the Neighbor
	Unreachability Detection algorithm. If the node is a router, it MUST		Unreachability Detection algorithm. If the node is a router, it MUST
	set the Router flag to one; otherwise it MUST set it to zero. The		set the Router flag to one; otherwise, it MUST set it to zero. The
	Override flag MAY be set to either zero or one. In either case,		Override flag MAY be set to either zero or one. In either case,
	neighboring nodes will immediately change the state of their Neighbor		neighboring nodes will immediately change the state of their Neighbor
	Cache entries for the Target Address to STALE, prompting them to		Cache entries for the Target Address to STALE, prompting them to
	verify the path for reachability. If the Override flag is set to		verify the path for reachability. If the Override flag is set to
	one, neighboring nodes will install the new link-layer address in		one, neighboring nodes will install the new link-layer address in
	their caches. Otherwise, they will ignore the new link-layer		their caches. Otherwise, they will ignore the new link-layer
	address, choosing instead to probe the cached address.		address, choosing instead to probe the cached address.
	A node that has multiple IP addresses assigned to an interface MAY		A node that has multiple IP addresses assigned to an interface MAY
	multicast a separate Neighbor Advertisement for each address. In		multicast a separate Neighbor Advertisement for each address. In
	such a case the node SHOULD introduce a small delay between the		such a case, the node SHOULD introduce a small delay between the
	sending of each advertisement to reduce the probability of the		sending of each advertisement to reduce the probability of the
	advertisements being lost due to congestion.		advertisements being lost due to congestion.
	A proxy MAY multicast Neighbor Advertisements when its link-layer		A proxy MAY multicast Neighbor Advertisements when its link-layer
	address changes or when it is configured (by system management or		address changes or when it is configured (by system management or
	other mechanisms) to proxy for an address. If there are multiple		other mechanisms) to proxy for an address. If there are multiple
	nodes that are providing proxy services for the same set of addresses		nodes that are providing proxy services for the same set of
	the proxies should provide a mechanism that prevents multiple proxies		addresses, the proxies should provide a mechanism that prevents
	from multicasting advertisements for any one address, in order to		multiple proxies from multicasting advertisements for any one
	reduce the risk of excessive multicast traffic. This is a requirement		address, in order to reduce the risk of excessive multicast traffic.
	on other protocols that need to use proxies for Neighbor		This is a requirement on other protocols that need to use proxies for
	Advertisements. An example of a node that performs proxy		Neighbor Advertisements. An example of a node that performs proxy
	advertisements is the Home Agent specified in [MIPv6].		advertisements is the Home Agent specified in [MIPv6].
	Also, a node belonging to an anycast address MAY multicast		Also, a node belonging to an anycast address MAY multicast
	unsolicited Neighbor Advertisements for the anycast address when the		unsolicited Neighbor Advertisements for the anycast address when the
	node's link-layer address changes.		node's link-layer address changes.
	Note that because unsolicited Neighbor Advertisements do not reliably		Note that because unsolicited Neighbor Advertisements do not reliably
	update caches in all nodes (the advertisements might not be received		update caches in all nodes (the advertisements might not be received
	by all nodes), they should only be viewed as a performance		by all nodes), they should only be viewed as a performance
	optimization to quickly update the caches in most neighbors. The		optimization to quickly update the caches in most neighbors. The
	skipping to change at page 62, line 44		skipping to change at page 68, line 25
	that has moved off-link. The mechanisms used by proxy are		that has moved off-link. The mechanisms used by proxy are
	essentially the same as the mechanisms used with anycast addresses.		essentially the same as the mechanisms used with anycast addresses.
	A proxy MUST join the solicited-node multicast address(es) that		A proxy MUST join the solicited-node multicast address(es) that
	correspond to the IP address(es) assigned to the node for which it is		correspond to the IP address(es) assigned to the node for which it is
	proxying. This SHOULD be done using a multicast listener discovery		proxying. This SHOULD be done using a multicast listener discovery
	protocol such as [MLD] or [MLDv2].		protocol such as [MLD] or [MLDv2].
	All solicited proxy Neighbor Advertisement messages MUST have the		All solicited proxy Neighbor Advertisement messages MUST have the
	Override flag set to zero. This ensures that if the node itself is		Override flag set to zero. This ensures that if the node itself is
	present on the link its Neighbor Advertisement (with the Override		present on the link, its Neighbor Advertisement (with the Override
	flag set to one) will take precedence of any advertisement received		flag set to one) will take precedence of any advertisement received
	from a proxy. A proxy MAY send unsolicited advertisements with the		from a proxy. A proxy MAY send unsolicited advertisements with the
	Override flag set to one as specified in Section 7.2.6, but doing so		Override flag set to one as specified in Section 7.2.6, but doing so
	may cause the proxy advertisement to override a valid entry created		may cause the proxy advertisement to override a valid entry created
	by the node itself.		by the node itself.
	Finally, when sending a proxy advertisement in response to a Neighbor		Finally, when sending a proxy advertisement in response to a Neighbor
	Solicitation, the sender should delay its response by a random time		Solicitation, the sender should delay its response by a random time
	between 0 and MAX_ANYCAST_DELAY_TIME seconds to avoid collisions due		between 0 and MAX_ANYCAST_DELAY_TIME seconds to avoid collisions due
	to multiple responses sent by several proxies. However, in some cases		to multiple responses sent by several proxies. However, in some
	(e.g. Mobile IPv6) where only one proxy is present, such delay is not		cases (e.g., Mobile IPv6) where only one proxy is present, such delay
	necessary.		is not necessary.
	7.3. Neighbor Unreachability Detection		7.3. Neighbor Unreachability Detection
	Communication to or through a neighbor may fail for numerous reasons		Communication to or through a neighbor may fail for numerous reasons
	at any time, including hardware failure, hot-swap of an interface		at any time, including hardware failure, hot-swap of an interface
	card, etc. If the destination has failed, no recovery is possible		card, etc. If the destination has failed, no recovery is possible
	and communication fails. On the other hand, if it is the path that		and communication fails. On the other hand, if it is the path that
	has failed, recovery may be possible. Thus, a node actively tracks		has failed, recovery may be possible. Thus, a node actively tracks
	the reachability "state" for the neighbors to which it is sending		the reachability "state" for the neighbors to which it is sending
	packets.		packets.
	skipping to change at page 63, line 42		skipping to change at page 69, line 25
	Neighbor Unreachability Detection is performed only for neighbors to		Neighbor Unreachability Detection is performed only for neighbors to
	which unicast packets are sent; it is not used when sending to		which unicast packets are sent; it is not used when sending to
	multicast addresses.		multicast addresses.
	7.3.1. Reachability Confirmation		7.3.1. Reachability Confirmation
	A neighbor is considered reachable if the node has recently received		A neighbor is considered reachable if the node has recently received
	a confirmation that packets sent recently to the neighbor were		a confirmation that packets sent recently to the neighbor were
	received by its IP layer. Positive confirmation can be gathered in		received by its IP layer. Positive confirmation can be gathered in
	two ways: hints from upper layer protocols that indicate a connection		two ways: hints from upper-layer protocols that indicate a connection
	is making "forward progress", or receipt of a Neighbor Advertisement		is making "forward progress", or receipt of a Neighbor Advertisement
	message that is a response to a Neighbor Solicitation message.		message that is a response to a Neighbor Solicitation message.
	A connection makes "forward progress" if the packets received from a		A connection makes "forward progress" if the packets received from a
	remote peer can only be arriving if recent packets sent to that peer		remote peer can only be arriving if recent packets sent to that peer
	are actually reaching it. In TCP, for example, receipt of a (new)		are actually reaching it. In TCP, for example, receipt of a (new)
	acknowledgement indicates that previously sent data reached the peer.		acknowledgment indicates that previously sent data reached the peer.
	Likewise, the arrival of new (non-duplicate) data indicates that		Likewise, the arrival of new (non-duplicate) data indicates that
	earlier acknowledgements are being delivered to the remote peer. If		earlier acknowledgments are being delivered to the remote peer. If
	packets are reaching the peer, they must also be reaching the		packets are reaching the peer, they must also be reaching the
	sender's next-hop neighbor; thus "forward progress" is a confirmation		sender's next-hop neighbor; thus, "forward progress" is a
	that the next-hop neighbor is reachable. For off-link destinations,		confirmation that the next-hop neighbor is reachable. For off-link
	forward progress implies that the first-hop router is reachable.		destinations, forward progress implies that the first-hop router is
	When available, this upper-layer information SHOULD be used.		reachable. When available, this upper-layer information SHOULD be
			used.
	In some cases (e.g., UDP-based protocols and routers forwarding		In some cases (e.g., UDP-based protocols and routers forwarding
	packets to hosts) such reachability information may not be readily		packets to hosts), such reachability information may not be readily
	available from upper-layer protocols. When no hints are available		available from upper-layer protocols. When no hints are available
	and a node is sending packets to a neighbor, the node actively probes		and a node is sending packets to a neighbor, the node actively probes
	the neighbor using unicast Neighbor Solicitation messages to verify		the neighbor using unicast Neighbor Solicitation messages to verify
	that the forward path is still working.		that the forward path is still working.
	The receipt of a solicited Neighbor Advertisement serves as		The receipt of a solicited Neighbor Advertisement serves as
	reachability confirmation, since advertisements with the Solicited		reachability confirmation, since advertisements with the Solicited
	flag set to one are sent only in response to a Neighbor Solicitation.		flag set to one are sent only in response to a Neighbor Solicitation.
	Receipt of other Neighbor Discovery messages such as Router
			Receipt of other Neighbor Discovery messages, such as Router
	Advertisements and Neighbor Advertisement with the Solicited flag set		Advertisements and Neighbor Advertisement with the Solicited flag set
	to zero MUST NOT be treated as a reachability confirmation. Receipt		to zero, MUST NOT be treated as a reachability confirmation. Receipt
	of unsolicited messages only confirms the one-way path from the		of unsolicited messages only confirms the one-way path from the
	sender to the recipient node. In contrast, Neighbor Unreachability		sender to the recipient node. In contrast, Neighbor Unreachability
	Detection requires that a node keep track of the reachability of the		Detection requires that a node keep track of the reachability of the
	forward path to a neighbor from its perspective, not the neighbor's		forward path to a neighbor from its perspective, not the neighbor's
	perspective. Note that receipt of a solicited advertisement		perspective. Note that receipt of a solicited advertisement
	indicates that a path is working in both directions. The solicitation		indicates that a path is working in both directions. The
	must have reached the neighbor, prompting it to generate an		solicitation must have reached the neighbor, prompting it to generate
	advertisement. Likewise, receipt of an advertisement indicates that		an advertisement. Likewise, receipt of an advertisement indicates
	the path from the sender to the recipient is working. However, the		that the path from the sender to the recipient is working. However,
	latter fact is known only to the recipient; the advertisement's		the latter fact is known only to the recipient; the advertisement's
	sender has no direct way of knowing that the advertisement it sent		sender has no direct way of knowing that the advertisement it sent
	actually reached a neighbor. From the perspective of Neighbor		actually reached a neighbor. From the perspective of Neighbor
	Unreachability Detection, only the reachability of the forward path		Unreachability Detection, only the reachability of the forward path
	is of interest.		is of interest.
	7.3.2. Neighbor Cache Entry States		7.3.2. Neighbor Cache Entry States
	A Neighbor Cache entry can be in one of five states:		A Neighbor Cache entry can be in one of five states:
	INCOMPLETE Address resolution is being performed on the entry.		INCOMPLETE Address resolution is being performed on the entry.
	skipping to change at page 65, line 9		skipping to change at page 70, line 48
	STALE More than ReachableTime milliseconds have elapsed		STALE More than ReachableTime milliseconds have elapsed
	since the last positive confirmation was received that		since the last positive confirmation was received that
	the forward path was functioning properly. While		the forward path was functioning properly. While
	stale, no action takes place until a packet is sent.		stale, no action takes place until a packet is sent.
	The STALE state is entered upon receiving an		The STALE state is entered upon receiving an
	unsolicited Neighbor Discovery message that updates		unsolicited Neighbor Discovery message that updates
	the cached link-layer address. Receipt of such a		the cached link-layer address. Receipt of such a
	message does not confirm reachability, and entering		message does not confirm reachability, and entering
	the STALE state insures reachability is verified		the STALE state ensures reachability is verified
	quickly if the entry is actually being used. However,		quickly if the entry is actually being used. However,
	reachability is not actually verified until the entry		reachability is not actually verified until the entry
	is actually used.		is actually used.
	DELAY More than ReachableTime milliseconds have elapsed		DELAY More than ReachableTime milliseconds have elapsed
	since the last positive confirmation was received that		since the last positive confirmation was received that
	the forward path was functioning properly, and a		the forward path was functioning properly, and a
	packet was sent within the last DELAY_FIRST_PROBE_TIME		packet was sent within the last DELAY_FIRST_PROBE_TIME
	seconds. If no reachability confirmation is received		seconds. If no reachability confirmation is received
	within DELAY_FIRST_PROBE_TIME seconds of entering the		within DELAY_FIRST_PROBE_TIME seconds of entering the
	DELAY state, send a Neighbor Solicitation and change		DELAY state, send a Neighbor Solicitation and change
	the state to PROBE.		the state to PROBE.
	The DELAY state is an optimization that gives upper-		The DELAY state is an optimization that gives upper-
	layer protocols additional time to provide		layer protocols additional time to provide
	reachability confirmation in those cases where		reachability confirmation in those cases where
	ReachableTime milliseconds have passed since the last		ReachableTime milliseconds have passed since the last
	confirmation due to lack of recent traffic. Without		confirmation due to lack of recent traffic. Without
	this optimization the opening of a TCP connection		this optimization, the opening of a TCP connection
	after a traffic lull would initiate probes even though		after a traffic lull would initiate probes even though
	the subsequent three-way handshake would provide a		the subsequent three-way handshake would provide a
	reachability confirmation almost immediately.		reachability confirmation almost immediately.
	PROBE A reachability confirmation is actively sought by		PROBE A reachability confirmation is actively sought by
	retransmitting Neighbor Solicitations every		retransmitting Neighbor Solicitations every
	RetransTimer milliseconds until a reachability		RetransTimer milliseconds until a reachability
	confirmation is received.		confirmation is received.
	7.3.3. Node Behavior		7.3.3. Node Behavior
	skipping to change at page 65, line 51		skipping to change at page 71, line 42
	sending of packets to a neighbor. While reasserting a neighbor's		sending of packets to a neighbor. While reasserting a neighbor's
	reachability, a node continues sending packets to that neighbor using		reachability, a node continues sending packets to that neighbor using
	the cached link-layer address. If no traffic is sent to a neighbor,		the cached link-layer address. If no traffic is sent to a neighbor,
	no probes are sent.		no probes are sent.
	When a node needs to perform address resolution on a neighboring		When a node needs to perform address resolution on a neighboring
	address, it creates an entry in the INCOMPLETE state and initiates		address, it creates an entry in the INCOMPLETE state and initiates
	address resolution as specified in Section 7.2. If address		address resolution as specified in Section 7.2. If address
	resolution fails, the entry SHOULD be deleted, so that subsequent		resolution fails, the entry SHOULD be deleted, so that subsequent
	traffic to that neighbor invokes the next-hop determination procedure		traffic to that neighbor invokes the next-hop determination procedure
	again. Invoking next-hop determination at this point insures that		again. Invoking next-hop determination at this point ensures that
	alternate default routers are tried.		alternate default routers are tried.
	When a reachability confirmation is received (either through upper-		When a reachability confirmation is received (either through upper-
	layer advice or a solicited Neighbor Advertisement) an entry's state		layer advice or a solicited Neighbor Advertisement), an entry's state
	changes to REACHABLE. The one exception is that upper-layer advice		changes to REACHABLE. The one exception is that upper-layer advice
	has no effect on entries in the INCOMPLETE state (e.g., for which no		has no effect on entries in the INCOMPLETE state (e.g., for which no
	link-layer address is cached).		link-layer address is cached).
	When ReachableTime milliseconds have passed since receipt of the last		When ReachableTime milliseconds have passed since receipt of the last
	reachability confirmation for a neighbor, the Neighbor Cache entry's		reachability confirmation for a neighbor, the Neighbor Cache entry's
	state changes from REACHABLE to STALE.		state changes from REACHABLE to STALE.
	Note: An implementation may actually defer changing the state from		Note: An implementation may actually defer changing the state from
	REACHABLE to STALE until a packet is sent to the neighbor, i.e.,		REACHABLE to STALE until a packet is sent to the neighbor, i.e.,
	there need not be an explicit timeout event associated with the		there need not be an explicit timeout event associated with the
	expiration of ReachableTime.		expiration of ReachableTime.
	The first time a node sends a packet to a neighbor whose entry is		The first time a node sends a packet to a neighbor whose entry is
	STALE, the sender changes the state to DELAY and a sets a timer to		STALE, the sender changes the state to DELAY and sets a timer to
	expire in DELAY_FIRST_PROBE_TIME seconds. If the entry is still in		expire in DELAY_FIRST_PROBE_TIME seconds. If the entry is still in
	the DELAY state when the timer expires, the entry's state changes to		the DELAY state when the timer expires, the entry's state changes to
	PROBE. If reachability confirmation is received, the entry's state		PROBE. If reachability confirmation is received, the entry's state
	changes to REACHABLE.		changes to REACHABLE.
	Upon entering the PROBE state, a node sends a unicast Neighbor		Upon entering the PROBE state, a node sends a unicast Neighbor
	Solicitation message to the neighbor using the cached link-layer		Solicitation message to the neighbor using the cached link-layer
	address. While in the PROBE state, a node retransmits Neighbor		address. While in the PROBE state, a node retransmits Neighbor
	Solicitation messages every RetransTimer milliseconds until		Solicitation messages every RetransTimer milliseconds until
	reachability confirmation is obtained. Probes are retransmitted even		reachability confirmation is obtained. Probes are retransmitted even
	if no additional packets are sent to the neighbor. If no response is		if no additional packets are sent to the neighbor. If no response is
	received after waiting RetransTimer milliseconds after sending the		received after waiting RetransTimer milliseconds after sending the
	MAX_UNICAST_SOLICIT solicitations, retransmissions cease and the		MAX_UNICAST_SOLICIT solicitations, retransmissions cease and the
	entry SHOULD be deleted. Subsequent traffic to that neighbor will		entry SHOULD be deleted. Subsequent traffic to that neighbor will
	recreate the entry and performs address resolution again.		recreate the entry and perform address resolution again.
	Note that all Neighbor Solicitations are rate-limited on a per-		Note that all Neighbor Solicitations are rate-limited on a per-
	neighbor basis. A node MUST NOT send Neighbor Solicitations to the		neighbor basis. A node MUST NOT send Neighbor Solicitations to the
	same neighbor more frequently than once every RetransTimer		same neighbor more frequently than once every RetransTimer
	milliseconds.		milliseconds.
	A Neighbor Cache entry enters the STALE state when created as a		A Neighbor Cache entry enters the STALE state when created as a
	result of receiving packets other than solicited Neighbor		result of receiving packets other than solicited Neighbor
	Advertisements (i.e., Router Solicitations, Router Advertisements,		Advertisements (i.e., Router Solicitations, Router Advertisements,
	Redirects, and Neighbor Solicitations). These packets contain the		Redirects, and Neighbor Solicitations). These packets contain the
	link-layer address of either the sender or, in the case of Redirect,		link-layer address of either the sender or, in the case of Redirect,
	the redirection target. However, receipt of these link-layer		the redirection target. However, receipt of these link-layer
	addresses does not confirm reachability of the forward-direction path		addresses does not confirm reachability of the forward-direction path
	to that node. Placing a newly created Neighbor Cache entry for which		to that node. Placing a newly created Neighbor Cache entry for which
	the link-layer address is known in the STALE state provides assurance		the link-layer address is known in the STALE state provides assurance
	that path failures are detected quickly. In addition, should a		that path failures are detected quickly. In addition, should a
	cached link-layer address be modified due to receiving one of the		cached link-layer address be modified due to receiving one of the
	above messages the state SHOULD also be set to STALE to provide		above messages, the state SHOULD also be set to STALE to provide
	prompt verification that the path to the new link-layer address is		prompt verification that the path to the new link-layer address is
	working.		working.
	To properly detect the case where a router switches from being a		To properly detect the case where a router switches from being a
	router to being a host (e.g., if its IP forwarding capability is		router to being a host (e.g., if its IP forwarding capability is
	turned off by system management), a node MUST compare the Router flag		turned off by system management), a node MUST compare the Router flag
	field in all received Neighbor Advertisement messages with the		field in all received Neighbor Advertisement messages with the
	IsRouter flag recorded in the Neighbor Cache entry. When a node		IsRouter flag recorded in the Neighbor Cache entry. When a node
	detects that a neighbor has changed from being a router to being a		detects that a neighbor has changed from being a router to being a
	host, the node MUST remove that router from the Default Router List		host, the node MUST remove that router from the Default Router List
	skipping to change at page 67, line 27		skipping to change at page 73, line 27
	again before using the entry.		again before using the entry.
	In some cases, link-specific information may indicate that a path to		In some cases, link-specific information may indicate that a path to
	a neighbor has failed (e.g., the resetting of a virtual circuit). In		a neighbor has failed (e.g., the resetting of a virtual circuit). In
	such cases, link-specific information may be used to purge Neighbor		such cases, link-specific information may be used to purge Neighbor
	Cache entries before the Neighbor Unreachability Detection would do		Cache entries before the Neighbor Unreachability Detection would do
	so. However, link-specific information MUST NOT be used to confirm		so. However, link-specific information MUST NOT be used to confirm
	the reachability of a neighbor; such information does not provide		the reachability of a neighbor; such information does not provide
	end-to-end confirmation between neighboring IP layers.		end-to-end confirmation between neighboring IP layers.
	8. REDIRECT FUNCTION		8. Redirect Function
	This section describes the functions related to the sending and		This section describes the functions related to the sending and
	processing of Redirect messages.		processing of Redirect messages.
	Redirect messages are sent by routers to redirect a host to a better		Redirect messages are sent by routers to redirect a host to a better
	first-hop router for a specific destination or to inform hosts that a		first-hop router for a specific destination or to inform hosts that a
	destination is in fact a neighbor (i.e., on-link). The latter is		destination is in fact a neighbor (i.e., on-link). The latter is
	accomplished by having the ICMP Target Address be equal to the ICMP		accomplished by having the ICMP Target Address be equal to the ICMP
	Destination Address.		Destination Address.
	A router MUST be able to determine the link-local address for each of		A router MUST be able to determine the link-local address for each of
	its neighboring routers in order to ensure that the target address in		its neighboring routers in order to ensure that the target address in
	a Redirect message identifies the neighbor router by its link-local		a Redirect message identifies the neighbor router by its link-local
	address. For static routing this requirement implies that the next-		address. For static routing, this requirement implies that the next-
	hop router's address should be specified using the link-local address		hop router's address should be specified using the link-local address
	of the router. For dynamic routing this requirement implies that all		of the router. For dynamic routing, this requirement implies that
	IPv6 routing protocols must somehow exchange the link-local addresses		all IPv6 routing protocols must somehow exchange the link-local
	of neighboring routers.		addresses of neighboring routers.
	8.1. Validation of Redirect Messages		8.1. Validation of Redirect Messages
	A host MUST silently discard any received Redirect message that does		A host MUST silently discard any received Redirect message that does
	not satisfy all of the following validity checks:		not satisfy all of the following validity checks:
	- IP Source Address is a link-local address. Routers must use		- IP Source Address is a link-local address. Routers must use
	their link-local address as the source for Router Advertisement		their link-local address as the source for Router Advertisement
	and Redirect messages so that hosts can uniquely identify		and Redirect messages so that hosts can uniquely identify
	routers.		routers.
	skipping to change at page 68, line 27		skipping to change at page 74, line 36
	- The ICMP Destination Address field in the redirect message does		- The ICMP Destination Address field in the redirect message does
	not contain a multicast address.		not contain a multicast address.
	- The ICMP Target Address is either a link-local address (when		- The ICMP Target Address is either a link-local address (when
	redirected to a router) or the same as the ICMP Destination		redirected to a router) or the same as the ICMP Destination
	Address (when redirected to the on-link destination).		Address (when redirected to the on-link destination).
	- All included options have a length that is greater than zero.		- All included options have a length that is greater than zero.
	The contents of the Reserved field, and of any unrecognized options		The contents of the Reserved field, and of any unrecognized options,
	MUST be ignored. Future, backward-compatible changes to the protocol		MUST be ignored. Future, backward-compatible changes to the protocol
	may specify the contents of the Reserved field or add new options;		may specify the contents of the Reserved field or add new options;
	backward-incompatible changes may use different Code values.		backward-incompatible changes may use different Code values.
	The contents of any defined options that are not specified to be used		The contents of any defined options that are not specified to be used
	with Redirect messages MUST be ignored and the packet processed as		with Redirect messages MUST be ignored and the packet processed as
	normal. The only defined options that may appear are the Target		normal. The only defined options that may appear are the Target
	Link-Layer Address option and the Redirected Header option.		Link-Layer Address option and the Redirected Header option.
	A host MUST NOT consider a redirect invalid just because the Target		A host MUST NOT consider a redirect invalid just because the Target
	skipping to change at page 68, line 49		skipping to change at page 75, line 9
	prefixes. Part of the semantics of the Redirect message is that the		prefixes. Part of the semantics of the Redirect message is that the
	Target Address is on-link.		Target Address is on-link.
	A redirect that passes the validity checks is called a "valid		A redirect that passes the validity checks is called a "valid
	redirect".		redirect".
	8.2. Router Specification		8.2. Router Specification
	A router SHOULD send a redirect message, subject to rate limiting,		A router SHOULD send a redirect message, subject to rate limiting,
	whenever it forwards a packet that is not explicitly addressed to		whenever it forwards a packet that is not explicitly addressed to
	itself (i.e. a packet that is not source routed through the router)		itself (i.e., a packet that is not source routed through the router)
	in which:		in which:
	- the Source Address field of the packet identifies a neighbor,		- the Source Address field of the packet identifies a neighbor,
	and		and
	- the router determines (by means outside the scope of this		- the router determines (by means outside the scope of this
	specification) that a better first-hop node resides on		specification) that a better first-hop node resides on the same
	the same link as the sending node for the Destination Address of		link as the sending node for the Destination Address of the
	the packet being forwarded, and		packet being forwarded, and
	- the Destination Address of the packet is not a multicast		- the Destination Address of the packet is not a multicast
	address		address.
	The transmitted redirect packet contains, consistent with the message		The transmitted redirect packet contains, consistent with the message
	format given in Section 4.5:		format given in Section 4.5:
	- In the Target Address field: the address to which subsequent		- In the Target Address field: the address to which subsequent
	packets for the destination should be sent. If the target is a		packets for the destination should be sent. If the target is a
	router, that router's link-local address MUST be used. If the		router, that router's link-local address MUST be used. If the
	target is a host the target address field MUST be set to the		target is a host, the target address field MUST be set to the
	same value as the Destination Address field.		same value as the Destination Address field.
	- In the Destination Address field: the destination address of the		- In the Destination Address field: the destination address of the
	invoking IP packet.		invoking IP packet.
	- In the options:		- In the options:
	o Target Link-Layer Address option: link-layer address of the		o Target Link-Layer Address option: link-layer address of the
	target, if known.		target, if known.
	skipping to change at page 69, line 50		skipping to change at page 76, line 12
	A router MUST NOT update its routing tables upon receipt of a		A router MUST NOT update its routing tables upon receipt of a
	Redirect.		Redirect.
	8.3. Host Specification		8.3. Host Specification
	A host receiving a valid redirect SHOULD update its Destination Cache		A host receiving a valid redirect SHOULD update its Destination Cache
	accordingly so that subsequent traffic goes to the specified target.		accordingly so that subsequent traffic goes to the specified target.
	If no Destination Cache entry exists for the destination, an		If no Destination Cache entry exists for the destination, an
	implementation SHOULD create such an entry.		implementation SHOULD create such an entry.
	If the redirect contains a Target Link-Layer Address option the host		If the redirect contains a Target Link-Layer Address option, the host
	either creates or updates the Neighbor Cache entry for the target.		either creates or updates the Neighbor Cache entry for the target.
	In both cases the cached link-layer address is copied from the Target		In both cases, the cached link-layer address is copied from the
	Link-Layer Address option. If a Neighbor Cache entry is created for		Target Link-Layer Address option. If a Neighbor Cache entry is
	the target its reachability state MUST be set to STALE as specified		created for the target, its reachability state MUST be set to STALE
	in Section 7.3.3. If a cache entry already existed and it is updated		as specified in Section 7.3.3. If a cache entry already existed and
	with a different link-layer address, its reachability state MUST also		it is updated with a different link-layer address, its reachability
	be set to STALE. If the link-layer address is the same as that		state MUST also be set to STALE. If the link-layer address is the
	already in the cache, the cache entry's state remains unchanged.		same as that already in the cache, the cache entry's state remains
			unchanged.
	If the Target and Destination Addresses are the same, the host MUST		If the Target and Destination Addresses are the same, the host MUST
	treat the Target as on-link. If the Target Address is not the same		treat the Target as on-link. If the Target Address is not the same
	as the Destination Address, the host MUST set IsRouter to TRUE for		as the Destination Address, the host MUST set IsRouter to TRUE for
	the target. If the Target and Destination Addresses are the same,		the target. If the Target and Destination Addresses are the same,
	however, one cannot reliably determine whether the Target Address is		however, one cannot reliably determine whether the Target Address is
	a router. Consequently, newly created Neighbor Cache entries should		a router. Consequently, newly created Neighbor Cache entries should
	set the IsRouter flag to FALSE, while existing cache entries should		set the IsRouter flag to FALSE, while existing cache entries should
	leave the flag unchanged. If the Target is a router, subsequent		leave the flag unchanged. If the Target is a router, subsequent
	Neighbor Advertisement or Router Advertisement messages will update		Neighbor Advertisement or Router Advertisement messages will update
	IsRouter accordingly.		IsRouter accordingly.
	Redirect messages apply to all flows that are being sent to a given		Redirect messages apply to all flows that are being sent to a given
	destination. That is, upon receipt of a Redirect for a Destination		destination. That is, upon receipt of a Redirect for a Destination
	Address, all Destination Cache entries to that address should be		Address, all Destination Cache entries to that address should be
	updated to use the specified next-hop, regardless of the contents of		updated to use the specified next-hop, regardless of the contents of
	the Flow Label field that appears in the Redirected Header option.		the Flow Label field that appears in the Redirected Header option.
	A host MUST NOT send Redirect messages.		A host MUST NOT send Redirect messages.
	9. EXTENSIBILITY - OPTION PROCESSING		9. Extensibility - Option Processing
	Options provide a mechanism for encoding variable length fields,		Options provide a mechanism for encoding variable length fields,
	fields that may appear multiple times in the same packet, or		fields that may appear multiple times in the same packet, or
	information that may not appear in all packets. Options can also be		information that may not appear in all packets. Options can also be
	used to add additional functionality to future versions of ND.		used to add additional functionality to future versions of ND.
	In order to ensure that future extensions properly coexist with		In order to ensure that future extensions properly coexist with
	current implementations, all nodes MUST silently ignore any options		current implementations, all nodes MUST silently ignore any options
	they do not recognize in received ND packets and continue processing		they do not recognize in received ND packets and continue processing
	the packet. All options specified in this document MUST be		the packet. All options specified in this document MUST be
	recognized. A node MUST NOT ignore valid options just because the ND		recognized. A node MUST NOT ignore valid options just because the ND
	message contains unrecognized ones.		message contains unrecognized ones.
	The current set of options is defined in such a way that receivers		The current set of options is defined in such a way that receivers
	can process multiple options in the same packet independently of each		can process multiple options in the same packet independently of each
	other. In order to maintain these properties future options SHOULD		other. In order to maintain these properties, future options SHOULD
	follow the simple rule:		follow the simple rule:
	The option MUST NOT depend on the presence or absence of any		The option MUST NOT depend on the presence or absence of any other
	other options. The semantics of an option should depend only on		options. The semantics of an option should depend only on the
	the information in the fixed part of the ND packet and on the		information in the fixed part of the ND packet and on the
	information contained in the option itself.		information contained in the option itself.
	Adhering to the above rule has the following benefits:		Adhering to the above rule has the following benefits:
	1) Receivers can process options independently of one another. For		1) Receivers can process options independently of one another. For
	example, an implementation can choose to process the Prefix		example, an implementation can choose to process the Prefix
	Information option contained in a Router Advertisement message		Information option contained in a Router Advertisement message
	in a user-space process while the link-layer address option in		in a user-space process while the link-layer address option in
	the same message is processed by routines in the kernel.		the same message is processed by routines in the kernel.
	skipping to change at page 71, line 30		skipping to change at page 77, line 46
	receivers should only act on the expiration of timers and on the		receivers should only act on the expiration of timers and on the
	information that is received in the packets.		information that is received in the packets.
	Options in Neighbor Discovery packets can appear in any order;		Options in Neighbor Discovery packets can appear in any order;
	receivers MUST be prepared to process them independently of their		receivers MUST be prepared to process them independently of their
	order. There can also be multiple instances of the same option in a		order. There can also be multiple instances of the same option in a
	message (e.g., Prefix Information options).		message (e.g., Prefix Information options).
	If the number of included options in a Router Advertisement causes		If the number of included options in a Router Advertisement causes
	the advertisement's size to exceed the link MTU, the router can send		the advertisement's size to exceed the link MTU, the router can send
	multiple separate advertisements each containing a subset of the		multiple separate advertisements, each containing a subset of the
	options.		options.
	The amount of data to include in the Redirected Header option MUST be		The amount of data to include in the Redirected Header option MUST be
	limited so that the entire redirect packet does not exceed the		limited so that the entire redirect packet does not exceed the
	minimum MTU required to support IPv6 as specified in [IPv6].		minimum MTU required to support IPv6 as specified in [IPv6].
	All options are a multiple of 8 octets of length, ensuring		All options are a multiple of 8 octets of length, ensuring
	appropriate alignment without any "pad" options. The fields in the		appropriate alignment without any "pad" options. The fields in the
	options (as well as the fields in ND packets) are defined to align on		options (as well as the fields in ND packets) are defined to align on
	their natural boundaries (e.g., a 16-bit field is aligned on a 16-bit		their natural boundaries (e.g., a 16-bit field is aligned on a 16-bit
	boundary) with the exception of the 128-bit IP addresses/prefixes,		boundary) with the exception of the 128-bit IP addresses/prefixes,
	which are aligned on a 64-bit boundary. The link-layer address field		which are aligned on a 64-bit boundary. The link-layer address field
	contains an uninterpreted octet string; it is aligned on an 8-bit		contains an uninterpreted octet string; it is aligned on an 8-bit
	boundary.		boundary.
	The size of an ND packet including the IP header is limited to the		The size of an ND packet including the IP header is limited to the
	link MTU. When adding options to an ND packet a node MUST NOT exceed		link MTU. When adding options to an ND packet, a node MUST NOT
	the link MTU.		exceed the link MTU.
	Future versions of this protocol may define new option types.		Future versions of this protocol may define new option types.
	Receivers MUST silently ignore any options they do not recognize and		Receivers MUST silently ignore any options they do not recognize and
	continue processing the message.		continue processing the message.
	10. PROTOCOL CONSTANTS		10. Protocol Constants
	Router constants:		Router constants:
	MAX_INITIAL_RTR_ADVERT_INTERVAL 16 seconds		MAX_INITIAL_RTR_ADVERT_INTERVAL 16 seconds
	MAX_INITIAL_RTR_ADVERTISEMENTS 3 transmissions		MAX_INITIAL_RTR_ADVERTISEMENTS 3 transmissions
	MAX_FINAL_RTR_ADVERTISEMENTS 3 transmissions		MAX_FINAL_RTR_ADVERTISEMENTS 3 transmissions
	MIN_DELAY_BETWEEN_RAS 3 seconds		MIN_DELAY_BETWEEN_RAS 3 seconds
	skipping to change at page 72, line 51		skipping to change at page 79, line 21
	MAX_RANDOM_FACTOR 1.5		MAX_RANDOM_FACTOR 1.5
	Additional protocol constants are defined with the message formats in		Additional protocol constants are defined with the message formats in
	Section 4.		Section 4.
	All protocol constants are subject to change in future revisions of		All protocol constants are subject to change in future revisions of
	the protocol.		the protocol.
	The constants in this specification may be overridden by specific		The constants in this specification may be overridden by specific
	documents that describe how IPv6 operates over different link-layers.		documents that describe how IPv6 operates over different link layers.
	This rule allows Neighbor Discovery to operate over links with widely		This rule allows Neighbor Discovery to operate over links with widely
	varying performance characteristics.		varying performance characteristics.
	11. SECURITY CONSIDERATIONS		11. Security Considerations
	Neighbor Discovery is subject to attacks that cause IP packets to		Neighbor Discovery is subject to attacks that cause IP packets to
	flow to unexpected places. Such attacks can be used to cause denial		flow to unexpected places. Such attacks can be used to cause denial
	of service but also allow nodes to intercept and optionally modify		of service but also allow nodes to intercept and optionally modify
	packets destined for other nodes. This section deals with the main		packets destined for other nodes. This section deals with the main
	threats related to Neighbor Discovery messages and possible security		threats related to Neighbor Discovery messages and possible security
	mechanisms that can mitigate these threats.		mechanisms that can mitigate these threats.
	11.1 Threat analysis		11.1. Threat Analysis
	This section discusses the main threats associated with Neighbor		This section discusses the main threats associated with Neighbor
	Discovery. A more detailed analysis can be found in [PSREQ]. The main		Discovery. A more detailed analysis can be found in [PSREQ]. The
	vulnerabilities of the protocol fall under three categories:		main vulnerabilities of the protocol fall under three categories:
	- Denial of Service (DoS) attacks.		- Denial-of-Service (DoS) attacks.
	- Address spoofing attacks.		- Address spoofing attacks.
	- Router spoofing attacks.		- Router spoofing attacks.
	An example of denial of service attacks is that a node on the link		An example of denial of service attacks is that a node on the link
	that can send packets with an arbitrary IP source address can both		that can send packets with an arbitrary IP source address can both
	advertise itself as a default router and also send "forged" Router		advertise itself as a default router and also send "forged" Router
	Advertisement messages that immediately time out all other default		Advertisement messages that immediately time out all other default
	routers as well as all on-link prefixes. An intruder can achieve		routers as well as all on-link prefixes. An intruder can achieve
	this by sending out multiple Router Advertisements, one for each		this by sending out multiple Router Advertisements, one for each
	legitimate router, with the source address set to the address of		legitimate router, with the source address set to the address of
	another router, the Router Lifetime field set to zero, and the		another router, the Router Lifetime field set to zero, and the
	Preferred and Valid lifetimes set to zero for all the prefixes. Such		Preferred and Valid lifetimes set to zero for all the prefixes. Such
	an attack would cause all packets, for both on-link and off-link		an attack would cause all packets, for both on-link and off-link
	destinations, to go to the rogue router. That router can then		destinations, to go to the rogue router. That router can then
	selectively examine, modify or drop all packets sent on the link. The		selectively examine, modify, or drop all packets sent on the link.
	Neighbor Unreachability Detection (NUD) will not detect such a black		The Neighbor Unreachability Detection (NUD) will not detect such a
	hole as long as the rogue router politely answers the NUD probes with		black hole as long as the rogue router politely answers the NUD
	a Neighbor Advertisement with the R-bit set.		probes with a Neighbor Advertisement with the R-bit set.
	It is also possible for any host to launch a DoS attack on another		It is also possible for any host to launch a DoS attack on another
	host by preventing it from configuring an address using [ADDRCONF].		host by preventing it from configuring an address using [ADDRCONF].
	The protocol does not allow hosts to verify whether the sender of a		The protocol does not allow hosts to verify whether the sender of a
	Neighbor Advertisement is the true owner of the IP address included		Neighbor Advertisement is the true owner of the IP address included
	in the message.		in the message.
	Redirect attacks can also be achieved by any host in order to flood a		Redirect attacks can also be achieved by any host in order to flood a
	victim or steal its traffic. A host can send a Neighbor advertisement		victim or steal its traffic. A host can send a Neighbor
	(in response to a solicitation) that contains its IP address and a		Advertisement (in response to a solicitation) that contains its IP
	victim's link-layer address in order to flood the victim with		address and a victim's link-layer address in order to flood the
	unwanted traffic. Alternatively, the host can send a Neighbor		victim with unwanted traffic. Alternatively, the host can send a
	Advertisement that includes a victim's IP address and its own link-		Neighbor Advertisement that includes a victim's IP address and its
	layer address to overwrite an existing entry in the sender's		own link-layer address to overwrite an existing entry in the sender's
	destination cache, thereby forcing the sender to forward all of the		destination cache, thereby forcing the sender to forward all of the
	victim's traffic to itself.		victim's traffic to itself.
	The trust model for redirects is the same as in IPv4. A redirect is		The trust model for redirects is the same as in IPv4. A redirect is
	accepted only if received from the same router that is currently		accepted only if received from the same router that is currently
	being used for that destination. If a host has been redirected to		being used for that destination. If a host has been redirected to
	another node (i.e., the destination is on-link) there is no way to		another node (i.e., the destination is on-link), there is no way to
	prevent the target from issuing another redirect to some other		prevent the target from issuing another redirect to some other
	destination. However, this exposure is no worse than it was before		destination. However, this exposure is no worse than it was before
	being redirected; the target host, once subverted, could always act		being redirected; the target host, once subverted, could always act
	as a hidden router to forward traffic elsewhere.		as a hidden router to forward traffic elsewhere.
	The protocol contains no mechanism to determine which neighbors are		The protocol contains no mechanism to determine which neighbors are
	authorized to send a particular type of message (e.g., Router		authorized to send a particular type of message (e.g., Router
	Advertisements); any neighbor, presumably even in the presence of		Advertisements); any neighbor, presumably even in the presence of
	authentication, can send Router Advertisement messages thereby being		authentication, can send Router Advertisement messages thereby being
	able to cause denial of service. Furthermore, any neighbor can send		able to cause denial of service. Furthermore, any neighbor can send
	proxy Neighbor Advertisements as well as unsolicited Neighbor		proxy Neighbor Advertisements as well as unsolicited Neighbor
	Advertisements as a potential denial of service attack.		Advertisements as a potential denial-of-service attack.
	Many link-layers are also subject to different denial of service		Many link layers are also subject to different denial-of-service
	attacks such as continuously occupying the link in CSMA/CD networks		attacks such as continuously occupying the link in CSMA/CD (Carrier
	(e.g., by sending packets closely back-to-back or asserting the		Sense Multiple Access with Collision Detection) networks (e.g., by
	collision signal on the link), or originating packets with somebody		sending packets closely back-to-back or asserting the collision
	else's source MAC address to confuse, e.g., Ethernet switches. On the		signal on the link), or originating packets with somebody else's
	other hand, many of the threats discussed in this section are less		source MAC address to confuse, e.g., Ethernet switches. On the other
			hand, many of the threats discussed in this section are less
	effective, or non-existent, on point-to-point links, or cellular		effective, or non-existent, on point-to-point links, or cellular
	links where a host shares a link with only one neighbor, i.e. the		links where a host shares a link with only one neighbor, i.e., the
	default router.		default router.
	11.2 Securing Neighbor Discovery messages		11.2. Securing Neighbor Discovery Messages
	The protocol reduces the exposure to the above threats in the absence		The protocol reduces the exposure to the above threats in the absence
	of authentication by ignoring ND packets received from off-link		of authentication by ignoring ND packets received from off-link
	senders. The Hop Limit field of all received packets is verified to		senders. The Hop Limit field of all received packets is verified to
	contain 255, the maximum legal value. Because routers decrement the		contain 255, the maximum legal value. Because routers decrement the
	Hop Limit on all packets they forward, received packets containing a		Hop Limit on all packets they forward, received packets containing a
	Hop Limit of 255 must have originated from a neighbor.		Hop Limit of 255 must have originated from a neighbor.
	Cryptographic security mechanisms for Neighbor Discovery are outside		Cryptographic security mechanisms for Neighbor Discovery are outside
	the scope of this document and are defined in [SEND]. Alternatively,		the scope of this document and are defined in [SEND]. Alternatively,
	skipping to change at page 75, line 7		skipping to change at page 81, line 34
	In some cases, it may be acceptable to use statically configured		In some cases, it may be acceptable to use statically configured
	security associations with either [IPv6-AUTH] or [IPv6-ESP] to secure		security associations with either [IPv6-AUTH] or [IPv6-ESP] to secure
	Neighbor Discovery messages. However, it is important to note that		Neighbor Discovery messages. However, it is important to note that
	statically configured security associations are not scalable		statically configured security associations are not scalable
	(especially when considering multicast links) and are therefore		(especially when considering multicast links) and are therefore
	limited to small networks with known hosts. In any case, if either		limited to small networks with known hosts. In any case, if either
	[IPv6-AUTH] or [IPv6-ESP] is used, ND packets MUST be verified for		[IPv6-AUTH] or [IPv6-ESP] is used, ND packets MUST be verified for
	the purpose of authentication. Packets that fail authentication		the purpose of authentication. Packets that fail authentication
	checks MUST be silently discarded.		checks MUST be silently discarded.
	12. RENUMBERING CONSIDERATIONS		12. Renumbering Considerations
	The Neighbor Discovery protocol together with IPv6 Address		The Neighbor Discovery protocol together with IPv6 Address
	Autoconfiguration [ADDRCONF] provides mechanisms to aid in		Autoconfiguration [ADDRCONF] provides mechanisms to aid in
	renumbering - new prefixes and addresses can be introduced and old		renumbering -- new prefixes and addresses can be introduced and old
	ones can be deprecated and removed.		ones can be deprecated and removed.
	The robustness of these mechanisms is based on all the nodes on the		The robustness of these mechanisms is based on all the nodes on the
	link receiving the Router Advertisement messages in a timely manner.		link receiving the Router Advertisement messages in a timely manner.
	However, a host might be turned off or be unreachable for an extended		However, a host might be turned off or be unreachable for an extended
	period of time (i.e., a machine is powered down for months after a		period of time (i.e., a machine is powered down for months after a
	project terminates). It is possible to preserve robust renumbering		project terminates). It is possible to preserve robust renumbering
	in such cases but it does place some constraints on how long prefixes		in such cases, but it does place some constraints on how long
	must be advertised.		prefixes must be advertised.
	Consider the following example in which a prefix is initially		Consider the following example in which a prefix is initially
	advertised with a lifetime of 2 months, but on August 1st it is		advertised with a lifetime of 2 months, but on August 1st it is
	determined that the prefix needs to be deprecated and removed due to		determined that the prefix needs to be deprecated and removed due to
	renumbering by September 1st. This can be done by reducing the		renumbering by September 1st. This can be done by reducing the
	advertised lifetime to 1 week starting on August 1st and as the		advertised lifetime to 1 week starting on August 1st, and as the
	cutoff gets closer the lifetimes can be made shorter until by		cutoff gets closer, the lifetimes can be made shorter until by
	September 1st the prefix is advertised with a zero lifetime. The		September 1st the prefix is advertised with a lifetime of 0. The
	point is that, if one or more nodes were unplugged from the link		point is that, if one or more nodes were unplugged from the link
	prior to September 1st they might still think that the prefix is		prior to September 1st, they might still think that the prefix is
	valid since the last lifetime they received was 2 months. Thus if a		valid since the last lifetime they received was 2 months. Thus, if a
	node was unplugged on July 31st it thinks the prefix is valid until		node was unplugged on July 31st, it thinks the prefix is valid until
	September 30th. If that node is plugged back in prior to September		September 30th. If that node is plugged back in prior to September
	30th it may continue to use the old prefix. The only way to force a		30th, it may continue to use the old prefix. The only way to force a
	node to stop using a prefix that was previously advertised with a		node to stop using a prefix that was previously advertised with a
	long Lifetime is to have that node receive an advertisement for that		long lifetime is to have that node receive an advertisement for that
	prefix that changes the lifetime downward. The solution in this		prefix that changes the lifetime downward. The solution in this
	example is simple: continue advertising the prefix with a lifetime of		example is simple: continue advertising the prefix with a lifetime of
	0 from September 1st until October 1st.		0 from September 1st until October 1st.
	In general, in order to be robust against nodes that might be		In general, in order to be robust against nodes that might be
	unplugged from the link it is important to track the furthest into		unplugged from the link, it is important to track the furthest into
	the future a particular prefix can be viewed valid by any node on the		the future that a particular prefix can be viewed as valid by any
	link. The prefix must then be advertised with a 0 Lifetime until		node on the link. The prefix must then be advertised with a 0
	that point in future. This "furthest into the future" time is simply		lifetime until that point in the future. This "furthest into the
	the maximum, over all Router Advertisements, of the time the		future" time is simply the maximum, over all Router Advertisements,
	advertisement was sent plus the prefix's Lifetime contained in the		of the time the advertisement was sent, plus the prefix's lifetime
	advertisement.		contained in the advertisement.
	The above has an important implication on using infinite lifetimes.		The above has an important implication on using infinite lifetimes.
	If a prefix is advertised with an infinite lifetime, and that prefix		If a prefix is advertised with an infinite lifetime, and that prefix
	later needs to be renumbered, it is undesirable to continue		later needs to be renumbered, it is undesirable to continue
	advertising that prefix with a zero lifetime forever. Thus either		advertising that prefix with a zero lifetime forever. Thus, either
	infinite lifetimes should be avoided or there must be a limit on how		infinite lifetimes should be avoided or there must be a limit on how
	long time a node can be unplugged from the link before it is plugged		long of a time a node can be unplugged from the link before it is
	back in again. However, it is unclear how the network administrator		plugged back in again. However, it is unclear how the network
	can enforce a limit on how long time hosts such as laptops can be		administrator can enforce a limit on how long time hosts such as
	unplugged from the link.		laptops can be unplugged from the link.
	Network administrators should give serious consideration to using		Network administrators should give serious consideration to using
	relatively short lifetimes (i.e., no more than a few weeks). While		relatively short lifetimes (i.e., no more than a few weeks). While
	it might appear that using long lifetimes would help insure		it might appear that using long lifetimes would help ensure
	robustness, in reality a host will be unable to communicate in the		robustness, in reality, a host will be unable to communicate in the
	absence of properly functioning routers. Such routers will be		absence of properly functioning routers. Such routers will be
	sending Router Advertisements that contain appropriate (and current)		sending Router Advertisements that contain appropriate (and current)
	prefixes. A host connected to a network that has no functioning		prefixes. A host connected to a network that has no functioning
	routers is likely to have more serious problems than just a lack of a		routers is likely to have more serious problems than just a lack of a
	valid prefix and address.		valid prefix and address.
	The above discussion does not distinguish between the preferred and		The above discussion does not distinguish between the preferred and
	valid lifetimes. For all practical purposes it is probably		valid lifetimes. For all practical purposes, it is probably
	sufficient to track the valid lifetime since the preferred lifetime		sufficient to track the valid lifetime since the preferred lifetime
	will not exceed the valid lifetime.		will not exceed the valid lifetime.
	IANA CONSIDERATIONS		13. IANA Considerations
	This document does not require any new ICMPv6 types or codes to be		This document does not require any new ICMPv6 types or codes to be
	allocated. However, existing ICMPv6 types should be updated to point		allocated. However, existing ICMPv6 types have been updated to point
	to the document instead of RFC 2461. The procedure for the assignment		to this document instead of RFC 2461. The procedure for the
	of ICMPv6 types/codes is described in Section 6 of [ICMPv6].		assignment of ICMPv6 types/codes is described in Section 6 of
			[ICMPv6].
	This document continues to use the following ICMPv6 message types		This document continues to use the following ICMPv6 message types
	introduced in RFC 2461 and already assigned by IANA:		introduced in RFC 2461 and already assigned by IANA:
	Message name ICMPv6 Type		Message name ICMPv6 Type
	Router Solicitation 133		Router Solicitation 133
	Router Advertisement 134		Router Advertisement 134
	Neighbor Solicitation 135		Neighbor Solicitation 135
	Neighbor Advertisement 136		Neighbor Advertisement 136
	skipping to change at page 77, line 4		skipping to change at page 83, line 39
	This document continues to use the following Neighbor Discovery		This document continues to use the following Neighbor Discovery
	option types introduced in RFC 2461 and already assigned by IANA:		option types introduced in RFC 2461 and already assigned by IANA:
	Option Name Type		Option Name Type
	Source Link-Layer Address 1		Source Link-Layer Address 1
	Target Link-Layer Address 2		Target Link-Layer Address 2
	Prefix Information 3		Prefix Information 3
	Redirected Header 4		Redirected Header 4
	MTU 5		MTU 5
	Neighbor Discovery option types are allocated using following
			Neighbor Discovery option types are allocated using the following
	procedure:		procedure:
	1. The IANA should allocate and permanently register new option types		1. The IANA should allocate and permanently register new option types
	from IETF RFC publication. This is for all RFC types		from IETF RFC publication. This is for all RFC types including
	including standards track, informational, and experimental status		standards track, informational, and experimental status that
	that originate from the IETF and have been approved by the IESG		originate from the IETF and have been approved by the IESG for
	for publication.		publication.
	2. IETF working groups with working group consensus and area director		2. IETF working groups with working group consensus and area director
	approval can request reclaimable Neighbor Discovery option type		approval can request reclaimable Neighbor Discovery option type
	assignments from the IANA. The IANA will tag the values as		assignments from the IANA. The IANA will tag the values as
	"reclaimable in future".		"reclaimable in future".
	The "reclaimable in the future" tag will be removed when an RFC is		The "reclaimable in the future" tag will be removed when an RFC is
	published documenting the protocol as defined in 1). This will		published documenting the protocol as defined in 1). This will make
	make the assignment permanent and update the reference on the IANA		the assignment permanent and update the reference on the IANA Web
	web pages.		pages.
	At the point where the option type values are 85% assigned, the		At the point where the option type values are 85% assigned, the IETF
	IETF will review the assignments tagged "reclaimable in the		will review the assignments tagged "reclaimable in the future" and
	future" and inform the IANA which ones should be reclaimed and		inform the IANA which ones should be reclaimed and reassigned.
	reassigned.
	3. Requests for new option type value assignments from outside the		3. Requests for new option type value assignments from outside the
	IETF are only made through the publication of an IETF document,		IETF are only made through the publication of an IETF document, per
	per 1) above. Note also that documents published as "RFC Editor		1) above. Note also that documents published as "RFC Editor
	contributions" [RFC3667] are not considered to be IETF documents.		contributions" [RFC3667] are not considered to be IETF documents.
	REFERENCES		14. References
	NORMATIVE		14.1. Normative References
	[ADDR-ARCH] Hinden, R. and S. Deering, "IP Version 6 Addressing		[ADDR-ARCH] Hinden, R. and S. Deering, "IP Version 6 Addressing
	Architecture", RFC 4291, February 2006.		Architecture", RFC 4291, February 2006.
	[ICMPv6] Conta, A. and S. Deering, "Internet Control Message		[ICMPv6] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
	Protocol (ICMPv6) for the Internet Protocol Version 6		Control Message Protocol (ICMPv6) for the Internet
	(IPv6) Specification", RFC 4443, March 2006.		Protocol Version 6 (IPv6) Specification", RFC 4443,
			March 2006.
	[IPv6] Deering, S. and R. Hinden, "Internet Protocol, Version 6		[IPv6] Deering, S. and R. Hinden, "Internet Protocol, Version 6
	(IPv6) Specification", RFC 2460, December 1998.		(IPv6) Specification", RFC 2460, December 1998.
	[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate		[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
	INFORMATIVE		14.2. Informative References
	[ADDRCONF] Thomson, S. Narten, T, and T. Jinmei, "IPv6 Address		[ADDRCONF] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
	Autoconfiguration", draft-ietf-ipv6-rfc2462bis-08, May		Address Autoconfiguration", RFC 4862, September 2007.
	2005.
	[ADDR-SEL] Draves, R., "Default Address Selection for Internet		[ADDR-SEL] Draves, R., "Default Address Selection for Internet
	Protocol version 6 (IPv6)", RFC 3484, February 2003.		Protocol version 6 (IPv6)", RFC 3484, February 2003.
	[ARP] Plummer, D., "An Ethernet Address Resolution Protocol",		[ARP] Plummer, D., "Ethernet Address Resolution Protocol: Or
	STD 37, RFC 826, November 1982.		Converting Network Protocol Addresses to 48.bit Ethernet
			Address for Transmission on Ethernet Hardware", STD 37,
			RFC 826, November 1982.
	[ASSIGNED] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by		[ASSIGNED] Reynolds, J., Ed., "Assigned Numbers: RFC 1700 is
	an On-line Database", RFC 3232, January 2002.		Replaced by an On-line Database", RFC 3232, January
			2002.
	[DHCPv6] Droms, R., Ed, "Dynamic Host Configuration Protocol for		[DHCPv6] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
	IPv6 (DHCPv6)", RFC 3315, July 2003.		C., and M. Carney, "Dynamic Host Configuration Protocol
			for IPv6 (DHCPv6)", RFC 3315, July 2003.
	[HR-CL] Braden, R., Editor, "Requirements for Internet Hosts --		[HR-CL] Braden, R., Ed., "Requirements for Internet Hosts -
	Communication Layers", STD 3, RFC 1122, October 1989.		Communication Layers", STD 3, RFC 1122, October 1989.
	[ICMPIKE] Arkko, J., "Effects of ICMPv6 on IKE",		[ICMPIKE] Arkko, J., "Effects of ICMPv6 on IKE", Work in Progress,
	draft-arkko-icmpv6-ike-effects-02 (work in progress),
	March 2003.		March 2003.
	[ICMPv4] Postel, J., "Internet Control Message Protocol", STD 5,		[ICMPv4] Postel, J., "Internet Control Message Protocol", STD 5,
	RFC 792, September 1981.		RFC 792, September 1981.
	[IPv6-3GPP] Wasserman, M., Ed, "Recommendations for IPv6 in Third		[IPv6-3GPP] Wasserman, M., Ed., "Recommendations for IPv6 in Third
	Generation Partnership Project (3GPP) standards", RFC		Generation Partnership Project (3GPP) Standards", RFC
	3314, September 2002.		3314, September 2002.
	[IPv6-CELL] Arkko, J., Kuipers, G., Soliman, H., Loughney, J. and J.		[IPv6-CELL] Arkko, J., Kuijpers, G., Soliman, H., Loughney, J., and
	Wiljakka, " Internet Protocol version 6 (IPv6) for Some		J. Wiljakka, "Internet Protocol Version 6 (IPv6) for
	Second and Third Generation Cellular Hosts", RFC 3316,		Some Second and Third Generation Cellular Hosts", RFC
	April 2003.		3316, April 2003.
	[IPv6-ETHER] Crawford, M., "Transmission of IPv6 Packets over		[IPv6-ETHER] Crawford, M., "Transmission of IPv6 Packets over
	Ethernet Networks", RFC 2464, December 1998.		Ethernet Networks", RFC 2464, December 1998.
	[IPv6-SA] Kent, S. and R. Atkinson, "Security Architecture for the		[IPv6-SA] Kent, S. and K. Seo, "Security Architecture for the
	Internet Protocol", RFC 4301, December 2005.		Internet Protocol", RFC 4301, December 2005.
	[IPv6-AUTH] S. Kent, "IP Authentication Header", RFC 4302, December		[IPv6-AUTH] Kent, S., "IP Authentication Header", RFC 4302, December
	2005.		2005.
	[IPv6-ESP] S. Kent, "IP Encapsulating Security Payload (ESP)", RFC		[IPv6-ESP] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
	4303, December 2005.		4303, December 2005.
	[IPv6-NBMA] Armitage, G., Schulter, P., Jork, M and G. Harter "IPv6		[IPv6-NBMA] Armitage, G., Schulter, P., Jork, M., and G. Harter,
	over Non-Broadcast Multiple Access (NBMA) networks", RFC		"IPv6 over Non-Broadcast Multiple Access (NBMA)
	2491, January 1999.		networks", RFC 2491, January 1999.
	[LD-SHRE] Hinden, R. and D. Thaler, "IPv6 Host-to-Router Load		[LD-SHRE] Hinden, R. and D. Thaler, "IPv6 Host-to-Router Load
	Sharing", RFC 4311, November 2005.		Sharing", RFC 4311, November 2005.
	[MIPv6] D. Johnson, C. Perkins and J. Arkko, "Mobility Support		[MIPv6] Johnson, D., Perkins, C., and J. Arkko, "Mobility
	in IPv6", RFC 3775, June 2004.		Support in IPv6", RFC 3775, June 2004.
	[MLD] Deering, S., Fenner, W, and B. Haberman, "Multicast		[MLD] Deering, S., Fenner, W., and B. Haberman, "Multicast
	Listener Discovery for IPv6", RFC 2710, October 1999.		Listener Discovery (MLD) for IPv6", RFC 2710, October
			1999.
	[MLDv2] Vida, R. and L. Costa, "Multicast Listener Discovery		[MLDv2] Vida, R., Ed., and L. Costa, Ed., "Multicast Listener
	Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.		Discovery Version 2 (MLDv2) for IPv6", RFC 3810, June
			2004.
	[PSREQ] Nikander, P., Kempf, J. And E. Nordmark, "IPv6 Neighbor		[PSREQ] Nikander, P., Ed., Kempf, J., and E. Nordmark, "IPv6
	Discovery (ND) Trust and Threats", RFC 3756, May 2004.		Neighbor Discovery (ND) Trust Models and Threats", RFC
	rd [RAND] Eastlake, 3 , D., Schiller, J and S. Crocker,		3756, May 2004.
	"Randomness Requirements for Security", RFC 4086, June
	2005.
	[RDISC] Deering, S., "ICMP Router Discovery Messages", RFC 1256,		[RAND] Eastlake, D., 3rd, Schiller, J., and S. Crocker,
	September 1991.		"Randomness Requirements for Security", BCP 106, RFC
			4086, June 2005.
			[RDISC] Deering, S., Ed., "ICMP Router Discovery Messages", RFC
			1256, September 1991.
	[RFC3667] Bradner, S., "IETF Rights in Contributions", RFC 3667,		[RFC3667] Bradner, S., "IETF Rights in Contributions", RFC 3667,
	February 2004.		February 2004.
	[RTSEL] Draves, R. and D. Thaler, "Default Router Preferences		[RTSEL] Draves, R. and D. Thaler, "Default Router Preferences
	and more Specific Routes", draft-ietf-ipv6-router-		and More-Specific Routes", RFC 4191, November 2005.
	selection-07, (work in progress), January 2005.
	[SH-MEDIA] Braden, R., Postel, J. and Y. Rekhter, "Internet		[SH-MEDIA] Braden, B., Postel, J., and Y. Rekhter, "Internet
	Architecture Extensions for Shared Media", RFC 1620, May		Architecture Extensions for Shared Media", RFC 1620, May
	1994.		1994.
	[SEND] Arkko, J., Kempf, J., Sommerfeld, B., Zill, B. and P.		[SEND] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
	Nikander, "SEcure Neighbor Discovery (SEND)",RFC3971,		"SEcure Neighbor Discovery (SEND)", RFC 3971, March
	March 2005.		2005.
	[SYNC] S. Floyd, V. Jacobson, "The Synchronization of Periodic		[SYNC] S. Floyd, V. Jacobson, "The Synchronization of Periodic
	Routing Messages", IEEE/ACM Transactions on Networking,		Routing Messages", IEEE/ACM Transactions on Networking,
	April 1994. ftp://ftp.ee.lbl.gov/papers/sync_94.ps.Z		April 1994. ftp://ftp.ee.lbl.gov/papers/sync_94.ps.Z
	Authors' Addresses		Appendix A: Multihomed Hosts
	Thomas Narten
	IBM Corporation
	P.O. Box 12195
	Research Triangle Park, NC 27709-2195
	USA
	Phone: +1 919 254 7798
	EMail: narten@us.ibm.com
	Erik Nordmark
	Sun Microsystems, Inc.
	901 San Antonio Road
	Palo Alto, CA 94303
	USA
	Phone: +1 650 786 5166
	Fax: +1 650 786 5896
	EMail: nordmark@sun.com
	William Allen Simpson
	Daydreamer
	Computer Systems Consulting Services
	1384 Fontaine
	Madison Heights, Michigan 48071
	USA
	EMail: Bill.Simpson@um.cc.umich.edu
	bsimpson@MorningStar.com
	Hesham Soliman
	Elevate Technologies
	Email: hesham@elevatemobile.com
	APPENDIX A: MULTIHOMED HOSTS
	There are a number of complicating issues that arise when Neighbor		There are a number of complicating issues that arise when Neighbor
	Discovery is used by hosts that have multiple interfaces. This		Discovery is used by hosts that have multiple interfaces. This
	section does not attempt to define the proper operation of multihomed		section does not attempt to define the proper operation of multihomed
	hosts with regard to Neighbor Discovery. Rather, it identifies		hosts with regard to Neighbor Discovery. Rather, it identifies
	issues that require further study. Implementors are encouraged to		issues that require further study. Implementors are encouraged to
	experiment with various approaches to making Neighbor Discovery work		experiment with various approaches to making Neighbor Discovery work
	on multihomed hosts and to report their experiences. Further work		on multihomed hosts and to report their experiences. Further work
	related to this problem can be found in [RTSEL].		related to this problem can be found in [RTSEL].
	skipping to change at page 81, line 7		skipping to change at page 87, line 35
	standard test for this case is to compare the source address of		standard test for this case is to compare the source address of
	the packet to the list of on-link prefixes associated with the		the packet to the list of on-link prefixes associated with the
	interface on which the packet was received. If the originating		interface on which the packet was received. If the originating
	host is multihomed, however, the source address it uses may		host is multihomed, however, the source address it uses may
	belong to an interface other than the interface from which it		belong to an interface other than the interface from which it
	was sent. In such cases, a router will not send redirects, and		was sent. In such cases, a router will not send redirects, and
	suboptimal routing is likely. In order to be redirected, the		suboptimal routing is likely. In order to be redirected, the
	sending host must always send packets out the interface		sending host must always send packets out the interface
	corresponding to the outgoing packet's source address. Note		corresponding to the outgoing packet's source address. Note
	that this issue never arises with non-multihomed hosts; they		that this issue never arises with non-multihomed hosts; they
	only have one interface. Additional discussion on this topic can		only have one interface. Additional discussion on this topic
	be found in RFC1122 under section 3.3.4.2.		can be found in RFC 1122 under Section 3.3.4.2.
	2) If the selected first-hop router does not have a route at all		2) If the selected first-hop router does not have a route at all
	for the destination, it will be unable to deliver the packet.		for the destination, it will be unable to deliver the packet.
	However, the destination may be reachable through a router on		However, the destination may be reachable through a router on
	one of the other interfaces. Neighbor Discovery does not		one of the other interfaces. Neighbor Discovery does not
	address this scenario; it does not arise in the non-multihomed		address this scenario; it does not arise in the non-multihomed
	case.		case.
	3) Even if the first-hop router does have a route for a		3) Even if the first-hop router does have a route for a
	destination, there may be a better route via another interface.		destination, there may be a better route via another interface.
	No mechanism exists for the multihomed host to detect this		No mechanism exists for the multihomed host to detect this
	situation.		situation.
	If a multihomed host fails to receive Router Advertisements on one or		If a multihomed host fails to receive Router Advertisements on one or
	more of its interfaces, it will not know (in the absence of		more of its interfaces, it will not know (in the absence of
	configured information) which destinations are on-link on the		configured information) which destinations are on-link on the
	affected interface(s). This leads to the following problem: If Router		affected interface(s). This leads to the following problem: If
	Advertisements are received on some, but not all interfaces, a		Router Advertisements are received on some, but not all, interfaces,
	multihomed host could choose to only send packets out on the		a multihomed host could choose to only send packets out on the
	interfaces on which it has received Router Advertisements. A key		interfaces on which it has received Router Advertisements. A key
	assumption made here, however, is that routers on those other		assumption made here, however, is that routers on those other
	interfaces will be able to route packets to the ultimate destination,		interfaces will be able to route packets to the ultimate destination,
	even when those destinations reside on the subnet to which the sender		even when those destinations reside on the subnet to which the sender
	connects, but has no on-link prefix information. Should the		connects, but has no on-link prefix information. Should the
	assumption be FALSE, communication would fail. Even if the assumption		assumption be FALSE, communication would fail. Even if the
	holds, packets will traverse a sub-optimal path.		assumption holds, packets will traverse a suboptimal path.
	APPENDIX B: FUTURE EXTENSIONS		Appendix B: Future Extensions
	Possible extensions for future study are:		Possible extensions for future study are:
	o Using dynamic timers to be able to adapt to links with widely		o Using dynamic timers to be able to adapt to links with widely
	varying delay. Measuring round trip times, however, requires		varying delay. Measuring round-trip times, however, requires
	acknowledgments and sequence numbers in order to match received		acknowledgments and sequence numbers in order to match received
	Neighbor Advertisements with the actual Neighbor Solicitation that		Neighbor Advertisements with the actual Neighbor Solicitation that
	triggered the advertisement. Implementors wishing to experiment		triggered the advertisement. Implementors wishing to experiment
	with such a facility could do so in a backwards-compatible way by		with such a facility could do so in a backwards-compatible way by
	defining a new option carrying the necessary information. Nodes		defining a new option carrying the necessary information. Nodes
	not understanding the option would simply ignore it.		not understanding the option would simply ignore it.
	o Adding capabilities to facilitate the operation over links that		o Adding capabilities to facilitate the operation over links that
	currently require hosts to register with an address resolution		currently require hosts to register with an address resolution
	server. This could for instance enable routers to ask hosts to		server. This could, for instance, enable routers to ask hosts to
	send them periodic unsolicited advertisements. Once again this		send them periodic unsolicited advertisements. Once again, this
	can be added using a new option sent in the Router Advertisements.		can be added using a new option sent in the Router Advertisements.
	o Adding additional procedures for links where asymmetric and non-		o Adding additional procedures for links where asymmetric and non-
	transitive reachability is part of normal operations. Such		transitive reachability is part of normal operations. Such
	procedures might allow hosts and routers to find usable paths on,		procedures might allow hosts and routers to find usable paths on,
	e.g., radio links.		e.g., radio links.
	APPENDIX C: STATE MACHINE FOR THE REACHABILITY STATE		Appendix C: State Machine for the Reachability State
	This appendix contains a summary of the rules specified in Sections		This appendix contains a summary of the rules specified in Sections
	7.2 and 7.3. This document does not mandate that implementations		7.2 and 7.3. This document does not mandate that implementations
	adhere to this model as long as their external behavior is consistent		adhere to this model as long as their external behavior is consistent
	with that described in this document.		with that described in this document.
	When performing address resolution and Neighbor Unreachability		When performing address resolution and Neighbor Unreachability
	Detection the following state transitions apply using the conceptual		Detection the following state transitions apply using the conceptual
	model:		model:
	skipping to change at page 84, line 28		skipping to change at page 91, line 30
	Different link-layer address		Different link-layer address
	address than cached.		address than cached.
	INCOMPLETE NS, RS No link-layer - unchanged		INCOMPLETE NS, RS No link-layer - unchanged
	address		address
	!INCOMPLETE NS, RS, RA, Redirect - unchanged		!INCOMPLETE NS, RS, RA, Redirect - unchanged
	Same link-layer		Same link-layer
	address as cached.		address as cached.
	APPENDIX D: SUMMARY OF ISROUTER RULES		Appendix D: Summary of IsRouter Rules
	This appendix presents a summary of the rules for maintaining the		This appendix presents a summary of the rules for maintaining the
	IsRouter flag as specified in this document.		IsRouter flag as specified in this document.
	The background for these rules is that the ND messages contain,		The background for these rules is that the ND messages contain,
	either implicitly or explicitly, information that indicates whether		either implicitly or explicitly, information that indicates whether
	or not the sender (or Target Address) is a host or a router. The		or not the sender (or Target Address) is a host or a router. The
	following assumptions are used:		following assumptions are used:
	- The sender of a Router Advertisement is implicitly assumed to be a		- The sender of a Router Advertisement is implicitly assumed to be a
	skipping to change at page 85, line 5		skipping to change at page 92, line 13
	flag", the R-bit.		flag", the R-bit.
	- The target of the redirect, when the target differs from the		- The target of the redirect, when the target differs from the
	destination address in the packet being redirected, is implicitly		destination address in the packet being redirected, is implicitly
	assumed to be a router. This is a natural assumption since that		assumed to be a router. This is a natural assumption since that
	node is expected to be able to forward the packets towards the		node is expected to be able to forward the packets towards the
	destination.		destination.
	- The target of the redirect, when the target is the same as the		- The target of the redirect, when the target is the same as the
	destination, does not carry any host vs. router information. All		destination, does not carry any host vs. router information. All
	that is known is that the destination (i.e. target) is on-link but		that is known is that the destination (i.e., target) is on-link
	it could be either a host or a router.		but it could be either a host or a router.
	The rules for setting the IsRouter flag are based on the information		The rules for setting the IsRouter flag are based on the information
	content above. If an ND message contains explicit or implicit		content above. If an ND message contains explicit or implicit
	information, the receipt of the message will cause the IsRouter flag		information, the receipt of the message will cause the IsRouter flag
	to be updated. But when there is no host vs. router information in		to be updated. But when there is no host vs. router information in
	the ND message the receipt of the message MUST NOT cause a change to		the ND message, the receipt of the message MUST NOT cause a change to
	the IsRouter state. When the receipt of such a message causes a		the IsRouter state. When the receipt of such a message causes a
	Neighbor Cache entry to be created this document specifies that the		Neighbor Cache entry to be created, this document specifies that the
	IsRouter flag be set to FALSE. There is greater potential for		IsRouter flag be set to FALSE. There is greater potential for
	mischief when a node incorrectly thinks a host is a router, than the		mischief when a node incorrectly thinks a host is a router, than the
	other way around. In these cases a subsequent Neighbor Advertisement		other way around. In these cases, a subsequent Neighbor
	or Router Advertisement message will set the correct IsRouter value.		Advertisement or Router Advertisement message will set the correct
			IsRouter value.
	APPENDIX E: IMPLEMENTATION ISSUES		Appendix E: Implementation Issues
	Appendix E.1: Reachability confirmations		E.1. Reachability Confirmations
	Neighbor Unreachability Detection requires explicit confirmation that		Neighbor Unreachability Detection requires explicit confirmation that
	a forward-path is functioning properly. To avoid the need for		a forward-path is functioning properly. To avoid the need for
	Neighbor Solicitation probe messages, upper layer protocols should		Neighbor Solicitation probe messages, upper-layer protocols should
	provide such an indication when the cost of doing so is small.		provide such an indication when the cost of doing so is small.
	Reliable connection-oriented protocols such as TCP are generally		Reliable connection-oriented protocols such as TCP are generally
	aware when the forward-path is working. When TCP sends (or receives)		aware when the forward-path is working. When TCP sends (or receives)
	data, for instance, it updates its window sequence numbers, sets and		data, for instance, it updates its window sequence numbers, sets and
	cancels retransmit timers, etc. Specific scenarios that usually		cancels retransmit timers, etc. Specific scenarios that usually
	indicate a properly functioning forward-path include:		indicate a properly functioning forward-path include:
	- Receipt of an acknowledgement that covers a sequence number (e.g.,		- Receipt of an acknowledgment that covers a sequence number (e.g.,
	data) not previously acknowledged indicates that the forward path		data) not previously acknowledged indicates that the forward path
	was working at the time the data was sent.		was working at the time the data was sent.
	- Completion of the initial three-way handshake is a special case of		- Completion of the initial three-way handshake is a special case of
	the previous rule; although no data is sent during the handshake,		the previous rule; although no data is sent during the handshake,
	the SYN flags are counted as data from the sequence number		the SYN flags are counted as data from the sequence number
	perspective. This applies to both the SYN+ACK for the active open		perspective. This applies to both the SYN+ACK for the active open
	the ACK of that packet on the passively opening peer.		and the ACK of that packet on the passively opening peer.
	- Receipt of new data (i.e., data not previously received) indicates		- Receipt of new data (i.e., data not previously received) indicates
	that the forward-path was working at the time an acknowledgement		that the forward-path was working at the time an acknowledgment
	was sent that advanced the peer's send window that allowed the new		was sent that advanced the peer's send window that allowed the new
	data to be sent.		data to be sent.
	To minimize the cost of communicating reachability information		To minimize the cost of communicating reachability information
	between the TCP and IP layers, an implementation may wish to rate-		between the TCP and IP layers, an implementation may wish to rate-
	limit the reachability confirmations its sends IP. One possibility		limit the reachability confirmations its sends IP. One possibility
	is to process reachability only every few packets. For example, one		is to process reachability only every few packets. For example, one
	might update reachability information once per round trip time, if an		might update reachability information once per round-trip time, if an
	implementation only has one round trip timer per connection. For		implementation only has one round-trip timer per connection. For
	those implementations that cache Destination Cache entries within		those implementations that cache Destination Cache entries within
	control blocks, it may be possible to update the Neighbor Cache entry		control blocks, it may be possible to update the Neighbor Cache entry
	directly (i.e., without an expensive lookup) once the TCP packet has		directly (i.e., without an expensive lookup) once the TCP packet has
	been demultiplexed to its corresponding control block. For other		been demultiplexed to its corresponding control block. For other
	implementations it may be possible to piggyback the reachability		implementations, it may be possible to piggyback the reachability
	confirmation on the next packet submitted to IP assuming that the		confirmation on the next packet submitted to IP assuming that the
	implementation guards against the piggybacked confirmation becoming		implementation guards against the piggybacked confirmation becoming
	stale when no packets are sent to IP for an extended period of time.		stale when no packets are sent to IP for an extended period of time.
	TCP must also guard against thinking "stale" information indicates		TCP must also guard against thinking "stale" information indicates
	current reachability. For example, new data received 30 minutes		current reachability. For example, new data received 30 minutes
	after a window has opened up does not constitute a confirmation that		after a window has opened up does not constitute a confirmation that
	the path is currently working; it merely indicates that 30 minutes		the path is currently working; it merely indicates that 30 minutes
	ago the window update reached the peer i.e. the path was working at		ago the window update reached the peer, i.e., the path was working at
	that point in time. An implementation must also take into account		that point in time. An implementation must also take into account
	TCP zero-window probes that are sent even if the path is broken and		TCP zero-window probes that are sent even if the path is broken and
	the window update did not reach the peer.		the window update did not reach the peer.
	For UDP based applications (RPC, DNS) it is relatively simple to make		For UDP-based applications (Remote Procedure Call (RPC), DNS), it is
	the client send reachability confirmations when the response packet		relatively simple to make the client send reachability confirmations
	is received. It is more difficult and in some cases impossible for		when the response packet is received. It is more difficult and in
	the server to generate such confirmations since there is no flow		some cases impossible for the server to generate such confirmations
	control, i.e., the server can not determine whether a received		since there is no flow control, i.e., the server cannot determine
	request indicates that a previous response reached the client.		whether a received request indicates that a previous response reached
			the client.
	Note that an implementation can not use negative upper-layer advice		Note that an implementation cannot use negative upper-layer advice as
	as a replacement for the Neighbor Unreachability Detection algorithm.		a replacement for the Neighbor Unreachability Detection algorithm.
	Negative advice (e.g., from TCP when there are excessive		Negative advice (e.g., from TCP when there are excessive
	retransmissions) could serve as a hint that the forward path from the		retransmissions) could serve as a hint that the forward path from the
	sender of the data might not be working. But it would fail to detect		sender of the data might not be working. But it would fail to detect
	when the path from the receiver of the data is not functioning,		when the path from the receiver of the data is not functioning,
	causing none of the acknowledgement packets to reach the sender.		causing none of the acknowledgment packets to reach the sender.
	APPENDIX F: CHANGES FROM RFC 2461		Appendix F: Changes from RFC 2461
	o Removed references to IPsec AH and ESP for securing messages		o Removed references to IPsec AH and ESP for securing messages or as
	or as part of validating the received message.		part of validating the received message.
	o Added section 3.3.		o Added Section 3.3.
	o Updated section 11 to include more detailed discussion on threats,		o Updated Section 11 to include more detailed discussion on threats,
	IPsec limitations, and use of SeND.		IPsec limitations, and use of SEND.
	o Removed the on-link assumption in section 5.2 based on		o Removed the on-link assumption in Section 5.2 based on RFC 4942,
	draft-ietf-v6ops-onlinkassumption		"IPv6 Neighbor Discovery On-Link Assumption Considered Harmful".
	o Clarified the definition of the Router Lifetime field in section		o Clarified the definition of the Router Lifetime field in Section
	4.2.		4.2.
	o Updated the text in section 4.6.2 and 6.2.1 to indicate that the		o Updated the text in Sections 4.6.2 and 6.2.1 to indicate that the
	preferred lifetime must not be larger than valid lifetime.		preferred lifetime must not be larger than valid lifetime.
	o Removed the reference to stateful configuration and added		o Removed the reference to stateful configuration and added reference
	reference for DHCPv6 instead.		for DHCPv6 instead.
	o Added the IsRouter flag definition to section 6.2.1 to allow for		o Added the IsRouter flag definition to Section 6.2.1 to allow for
	mixed host/router behavior.		mixed host/router behavior.
	o Allowed mobile nodes to be exempt from adding random delays before		o Allowed mobile nodes to be exempt from adding random delays before
	sending an RS during a handover.		sending an RS during a handover.
	o Updated the definition of the prefix length in the prefix option		o Updated the definition of the prefix length in the prefix option.
	o Updated the applicability to NBMA links in the introduction and		o Updated the applicability to NBMA links in the introduction and
	added references to 3GPP RFCs.		added references to 3GPP RFCs.
	o Clarified support for Load balancing is limited to routers.		o Clarified that support for load balancing is limited to routers.
	o Clarified router behaviour when receiving a Router Solicitation		o Clarified router behavior when receiving a Router Solicitation
	without SLLAO.		without Source Link-Layer Address Option (SLLAO).
	o Clarified that inconsistency checks for CurHopLimit are done for		o Clarified that inconsistency checks for CurHopLimit are done for
	non-zero values only.		non-zero values only.
	o Rearranged section 7.2.5 for clarity and described the processing		o Rearranged Section 7.2.5 for clarity, and described the processing
	when receiving the NA in INCOMPLETE state.		when receiving the NA in INCOMPLETE state.
	o Added clarifications in section 7.2 on how a node should react		o Added clarifications in Section 7.2 on how a node should react upon
	upon receiving a message without SLLAO.		receiving a message without SLLAO.
	O Added New IANA section.		o Added new IANA section.
	o Miscellaneous editorials.		o Miscellaneous editorials.
	Intellectual Property Statement		Acknowledgments
			The authors of RFC 2461 would like to acknowledge the contributions
			of the IPV6 working group and, in particular, (in alphabetical order)
			Ran Atkinson, Jim Bound, Scott Bradner, Alex Conta, Stephen Deering,
			Richard Draves, Francis Dupont, Robert Elz, Robert Gilligan, Robert
			Hinden, Tatuya Jinmei, Allison Mankin, Dan McDonald, Charles Perkins,
			Matt Thomas, and Susan Thomson.
			The editor of this document (Hesham Soliman) would like to thank the
			IPV6 working group for the numerous contributions to this revision --
			in particular (in alphabetical order), Greg Daley, Elwyn Davies,
			Ralph Droms, Brian Haberman, Bob Hinden, Tatuya Jinmei, Pekka Savola,
			Fred Templin, and Christian Vogt.
			Authors' Addresses
			Thomas Narten
			IBM Corporation
			P.O. Box 12195
			Research Triangle Park, NC 27709-2195
			USA
			Phone: +1 919 254 7798
			EMail: narten@us.ibm.com
			Erik Nordmark
			Sun Microsystems, Inc.
			17 Network Circle
			Menlo Park, CA 94025
			USA
			Phone: +1 650 786 2921
			Fax: +1 650 786 5896
			EMail: erik.nordmark@sun.com
			William Allen Simpson
			Daydreamer
			Computer Systems Consulting Services
			1384 Fontaine
			Madison Heights, Michigan 48071
			USA
			EMail: william.allen.simpson@gmail.com
			Hesham Soliman
			Elevate Technologies
			EMail: hesham@elevatemobile.com
			Full Copyright Statement
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			retain all their rights.
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			Intellectual Property
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	Intellectual Property Rights or other rights that might be claimed to		Intellectual Property Rights or other rights that might be claimed to
	pertain to the implementation or use of the technology described in		pertain to the implementation or use of the technology described in
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	Full Copyright Statement
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	This Internet-Draft expires September, 2007.
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