draft-ietf-vrrp-spec-00.txt		draft-ietf-vrrp-spec-01.txt
	INTERNET-DRAFT S. Knight		INTERNET-DRAFT S. Knight
	June 22, 1997 Ascend Communications, Inc.		July 28, 1997 D. Weaver
	D. Weaver
	Ascend Communications, Inc.		Ascend Communications, Inc.
	D. Whipple		D. Whipple
	Microsoft, Inc.		Microsoft, Inc.
	R. Hinden		R. Hinden
			D. Mitzel
	Ipsilon Networks, Inc.		Ipsilon Networks, Inc.
	Virtual Router Redundancy Protocol		Virtual Router Redundancy Protocol
	<draft-ietf-vrrp-spec-00.txt>		<draft-ietf-vrrp-spec-01.txt>
	Status of this Memo		Status of this Memo
	This document is an Internet-Draft. Internet-Drafts are working		This document is an Internet-Draft. Internet-Drafts are working
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	This internet draft expires on December 23, 1997.		This internet draft expires on January 29, 1998.
	Abstract		Abstract
	The memo documents the Virtual Router Redundancy Protocol. This is a		This memo defines the Virtual Router Redundancy Protocol (VRRP).
	protocol which allows several routers to utilize the same virtual IP		VRRP specifies an election protocol that dynamically assigns
	address. One router will be elected as a master, with X routers		responsibility for a virtual IP address to a single router among a
	acting as backups in case of failure of the master router. The		collection of VRRP routers. The VRRP router controlling the virtual
	primary advantage to utilizing this protocol, is that host systems		IP address is called the Master router, and forwards packets sent to
	may be configured with a single default gateway, rather than running		the virtual IP address. The election process provides dynamic fail
	an active routing protocol. Each interface on each router within a		over in the forwarding responsibility should the Master become
	VRRP cluster, will be configured with a real IP address, and the		unavailable. The virtual IP address can then be used as the default
	virtual IP address for the particular cluster. Overall, this		first hop router by end-hosts. The advantage gained from using the
	protocol adds to the options for providing fault redundancy for		VRRP virtual IP address is a higher availability default path without
	router networks.		requiring configuration of dynamic routing or router discovery
			protocols on every end-host.
	Table Of Contents		This memo describes the features and theory of operation of VRRP.
			The protocol processing and state machine that guarantee convergence
			to a single Master router is presented. Also issues related to MAC
			address mapping, handling ARP requests, generating ICMP redirects,
			and security issues are addressed.
			Table of Contents
	1. Introduction...............................................3		1. Introduction...............................................3
	2. Scope......................................................3		2. Scope......................................................4
	3. Definitions................................................4		3. Definitions................................................6
	4. Sample Configurations......................................4		4. Sample Configurations......................................8
	4.1 Sample Configuration 1................................4		4.1 Sample Configuration 1................................8
	4.2 Sample Configuration 2................................5		4.2 Sample Configuration 2................................9
	5. Protocol...................................................6		5. Protocol..................................................10
	5.1 VRRP Packet Format....................................6		5.1 VRRP Packet Format...................................10
	5.2 IP Field Descriptions.................................6		5.2 IP Field Descriptions................................10
	5.3 VRRP Field Descriptions...............................7		5.3 VRRP Field Descriptions..............................11
	6. Protocol State Machine.....................................9		6. Protocol State Machine....................................14
	6.1 Parameters..............................................9		6.1 Parameters.............................................14
	6.2 Timers.................................................10		6.2 Timers.................................................14
	6.3 State Transition Diagram..............................10		6.3 State Transition Diagram..............................15
	6.4 State Descriptions....................................10		6.4 State Descriptions....................................15
	6.5 State Table...........................................12		7. Sending and Receiving VRRP Packets........................18
	7. Sending and Receiving VRRP Packets........................14		7.1 Receiving VRRP Packets................................18
	7.1 Receiving VRRP Packets................................14		7.2 Transmitting Packets...................................18
	7.2 Transmitting Packets...................................14		7.3 Virtual MAC Address....................................19
	7.3 Virtual MAC Address....................................15		8. Host Operation............................................19
	8. Host Operation............................................15		8.1 Host ARP Requests....................................19
	8.1 Host ARP Requests....................................15		9. Operational Issues........................................19
	9. Operational Issues........................................15		9.1 ICMP Redirects.........................................19
	9.1 ICMP Redirects.........................................15		9.2 Proxy ARP..............................................19
	9.2 Proxy ARP..............................................15		9.3 Network Management.....................................19
	9.3 Network Management.....................................16		10. Operation over FDDI and Token Ring.......................20
	10. Operation over Token Ring.................................16		11. Security Considerations...................................21
	11. References................................................17		11.1 No Authentication.....................................21
	12. Security Considerations...................................17		11.2 Simple Text Password..................................21
	13. Authors' Addresses........................................17		11.3 IP Authentication Header..............................21
	14. Acknowledgments...........................................17		12. References................................................23
	15. Changes from Previous Drafts..............................18		13. Authors' Addresses........................................23
			14. Acknowledgments...........................................24
			15. Changes from Previous Drafts..............................25
	1. Introduction		1. Introduction
	The reason for the development of VRRP is to create a standard		There are a number of methods that an end-host can use to determine
	protocol, with multi-vendor support to resolve the problem of router		its first hop router towards a particular IP destination. These
	failure. Specifically, when a single router is utilized as a default		include running (or snooping) a dynamic routing protocol such as
	gateway, and all hosts are statically configured to this default		Routing Information Protocol [RIP] or OSPF version 2 [OSPF], running
	gateway, a failure is catastrophic. VRRP resolves this problem by		an ICMP router discovery client [DISC] or using a statically
	creating virtual clusters, where each cluster is configured with a		configured default route.
	set of member routers. Each member router is either a master router
	for the cluster or a backup router for the cluster, but not both
	simultaneously. In addition, there MUST only be a single master
	router per cluster, at any given time. All member routers are
	configured to be part of a cluster, with a given virtual IP address.
	This virtual IP address is utilized as the default gateway on all of
	the host systems. Given a failure on the current master router, the
	next appropriate backup router will become the master router for the
	given cluster. When routers are configured with the equal priority
	the router which is master will stay master as long as it is up.
	Of course this problem could be solved by running a standard routing		Running a dynamic routing protocol on every end-host may be
	protocol such as OSPF, RIP, or RIPv2 on the hosts. However, this is		infeasible for a number of reasons, including administrative
	not always feasible due to either security issues, when hosts are		overhead, processing overhead, security issues, or lack of a protocol
	multihomed, or in some cases implementations of these routing		implementation for some platforms. Neighbor or router discovery
	protocols simply do not exist.		protocols may require active participation by all hosts on a network,
			leading to large timer values to reduce protocol overhead in the face
			of large numbers of hosts. This can result in a significant delay in
			the detection of a lost (i.e., dead) neighbor, which may introduce
			unacceptably long "black hole" periods.
			The use of a statically configured default route is quite popular; it
			minimizes configuration and processing overhead on the end-host and
			is supported by virtually every IP implementation. This mode of
			operation is likely to persist as dynamic host configuration
			protocols [DHCP] are deployed, which typically provide configuration
			for an end-host IP address and default gateway. However, this
			creates a single point of failure. Loss of the default router
			results in a catastrophic event, isolating all end-hosts that are
			unable to detect any alternate path that may be available.
			The Virtual Router Redundancy Protocol (VRRP) is designed to
			eliminate the single point of failure inherent in the static default
			routed environment. VRRP specifies an election protocol that
			dynamically assigns responsibility for a virtual IP address to a
			single router among a collection of VRRP routers. The VRRP router
			controlling the virtual IP address is called the Master router, and
			forwards packets sent to the virtual IP address. The election
			process provides dynamic fail-over in the forwarding responsibility
			should the Master become unavailable. The virtual IP address can
			then be used as the default first hop router by end-hosts. The
			advantage gained from using the VRRP virtual IP address is a higher
			availability default path without requiring configuration of dynamic
			routing or router discovery protocols on every end-host.
			VRRP provides a function similar to a Cisco Systems, Inc. proprietary
			protocol named Hot Standby Router Protocol (HSRP) [HSRP].
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in [RFC 2119].		document are to be interpreted as described in [RFC 2119].
	2. Scope		1.1 Scope
	This memo describes the Virtual Router Redundancy Protocol.		The remainder of this document describes the features, design goals,
			and theory of operation of VRRP. The message formats, protocol
			processing rules and state machine that guarantee convergence to a
			single Master router are presented. Finally, operational issues
			related to MAC address mapping, handling of ARP requests, generation
			of ICMP redirect messages, and security issues are addressed.
	This protocol is intended for IPv4 only. A version for IPv6 will be		This protocol is intended for use with IPv4 routers only. A separate
	defined in a separate specification.		specification will be produced if it is decided that similar
			functionality is desirable in an IPv6 environment.
	Within the scope of this specification are:		1.2 Definitions
	1. Packet format and header contents.		Cluster The set of routers participating in VRRP to emulate a
	2. State Diagrams and Descriptions		virtual router.
	3. Network Design Samples
	Outside of the scope are		Master Router The VRRP router controlling the virtual IP address
			and assuming the responsibility of forwarding packets
			sent to the virtual router.
	1. Network management		Backup Router The set of routers in the quiescent state with regard
	2. Host internal optimizations		to the virtual router operation. This set includes
			all active VRRP routers within a cluster that are not
			the Master router.
	3. Definitions		2.0 Required Features
	Cluster		This section outlines the set of features that were considered
			mandatory and that guided the design of VRRP.
	Used to describe a set of routers who all have membership to the		2.1 Virtual IP Management
	set of routers S, where S contains all routers configured with
	the same virtual IP address.
	Master Router		Management of the virtual IP address is the primary function of the
			virtual router protocol. While providing election of a Master router
			and the additional functionality described below, the protocol should
			strive to:
	Used to describe the currently active router, for a particular		- Minimize the duration of black holes.
	cluster, with a particular virtual IP address. Their can only be		- Minimize the steady state bandwidth overhead and processing
	one master router in a particular cluster.		complexity.
			- Function over a wide variety of multiaccess LAN technologies
			capable of supporting IP traffic.
			- Provide for election of multiple virtual routers on a network for
			load balancing or in support of multiple logical IP subnets on a
			single LAN segment.
	Backup Router		2.2 Preferred Path Indication
	Used to describe a router which is configured to act as a backup		A simple model of Master election among a set of redundant routers is
	for a particular cluster. There can be several backup routers in		to treat each router with equal preference and claim victory after
	a single cluster.		converging to any router as Master. However, there are likely to be
			many environments where there is a distinct preference (or range of
			preferences) among the set of redundant routers. For example, this
			preference may be based upon access link cost or speed, router
			performance or reliability, or other policy considerations. The
			protocol should allow the expression of this relative path preference
			in an intuitive manner, and guarantee Master convergence to the most
			preferential router currently available.
			2.3 Minimization of Unnecessary Service Disruptions
			Once Master election has been performed then any unnecessary
			transitions between Master and Backup routers can result in a
			disruption in service. The protocol should ensure after Master
			election that no state transition is triggered by any Backup router
			of equal or lower preference as long as the Master continues to
			function properly.
			Some environments may find it beneficial to avoid the state
			transition triggered when a router becomes available that is more
			preferential than the current Master. It may be useful to support an
			override of the immediate convergence to the preferred path.
			2.4 Extensible Security
			The virtual router functionality is applicable to a wide range of
			internetworking environments that may employ different security
			policies. The protocol should require minimal configuration and
			overhead in the insecure operation, provide for strong authentication
			when increased security is required, and allow integration of new
			security mechanisms without breaking backwards compatible operation.
			2.5 Efficient Operation over Extended LANs
			Sending IP packets on a multiaccess LAN requires mapping from the
			virtual IP address to a MAC address. The use of the virtual router
			MAC address in an extended LAN employing learning bridges can have a
			significant effect on the bandwidth overhead of packets sent to the
			virtual router. If the virtual router MAC address is never used as
			the source address in a link level frame then the station location is
			never learned, resulting in flooding of all packets sent to the
			virtual router. To improve the efficiency in this environment the
			protocol should: 1) use the virtual router MAC as the source in a
			packet sent by the Master to trigger station learning; 2) trigger a
			message immediately after transitioning to Master to update the
			station learning; and 3) trigger periodic messages from the Master to
			maintain the station learning cache.
			3.0 VRRP Overview
			VRRP assumes that each router has a consistent set of routes. The
			mechanism used to learn or configure this routing state and ensure
			its consistency is beyond the scope of this specification.
			VRRP specifies an election protocol to provide the virtual router
			function described earlier. All protocol messaging is performed
			using IP multicast datagrams, thus the protocol can operate over a
			variety of multiaccess LAN technologies supporting IP multicast.
			Each VRRP virtual router has a single well-known MAC address
			allocated to it. This document currently only details the mapping to
			networks using the IEEE 802 48-bit MAC address. The virtual router
			MAC address is used as the source in all periodic messages sent by
			the Master router to enable bridge learning in an extended LAN.
			A virtual router is identified by its virtual IP address, and
			associated with a VRRP cluster. The virtual IP address must not
			match the real IP address of any host or the virtual IP address of
			any other VRRP cluster on the LAN. Each VRRP router assigned to the
			cluster must be configured with the same virtual IP address and must
			have a real IP address with a prefix matching the virtual router
			address. In addition, each VRRP router is assigned a priority to
			indicate the preference for Master election. Multiple virtual
			routers can be elected on a network by associating them with
			different VRRP clusters, and a single router can participate in
			multiple VRRP clusters by maintaining independent state machines for
			each cluster.
			To minimize network traffic, only the Master router sends periodic
			Advertisement messages. A Backup router will not attempt to pre-empt
			the Master unless it has higher priority. This eliminates service
			disruption unless a more preferred path becomes available; it's also
			possible to administratively prohibit all pre-emption attempts. If
			the Master becomes unavailable then the highest priority Backup will
			transition to Master after a short delay, providing a controlled
			transition of the virtual router responsibility with minimal service
			interruption.
			VRRP defines three types of authentication providing simple
			deployment in insecure environments, added protection against
			misconfiguration, and strong sender authentication in security
			conscious environments. Analysis of the protection provided and
			vulnerability of each mechanism is deferred to Section 11.0 Security
			Considerations. In addition new authentication types and data can be
			defined in the future without affecting the format of the fixed
			portion of the protocol packet, thus preserving backward compatible
			operation.
			The VRRP protocol design provides rapid transition from Backup to
			Master to minimize service interruption, and incorporates
			optimizations that reduce protocol complexity while guaranteeing
			controlled Master transition for typical operational scenarios. The
			optimizations result in an election protocol with minimal runtime
			state requirements, minimal active protocol states, and a single
			message type and sender. The typical operational scenarios are
			defined to be two redundant routers in a VRRP cluster (i.e., a Master
			and one Backup), and/or distinct path preferences among each router.
			A side effect when these assumptions are violated (i.e., more than
			two redundant paths all with equal preference) is that duplicate
			packets may be forwarded for a brief period during Master election.
			However, the typical scenario assumptions are likely to cover the
			vast majority of deployments, loss of the Master router is
			infrequent, and the expected duration in Master election convergence
			is quite small ( << 1 second ). Thus the VRRP optimizations
			represent significant simplifications in the protocol design while
			incurring an insignificant probability of brief network degradation.
	4. Sample Configurations		4. Sample Configurations
	4.1 Sample Configuration 1		4.1 Sample Configuration 1
	The following figure shows a simple VRRP network.		The following figure shows a simple VRRP network.
	+--------------------------+		+--------------------------+
	| Cluster X |		| Cluster X |
	| |		| |
	| +-----+ +-----+ |		| +-------+ +-------+ |
	| | MRX | | BRX | |		| | MRX | | BRX | |
	| +-----+ +-----+ |		| | | | | |
			| |(P=200)| |(P=100)| |
			| | | | | |
			| +-------+ +-------+ |
	Real IP 1 ---------->* *<---------- Real IP 2		Real IP 1 ---------->* *<---------- Real IP 2
	| | * | |		| | * | |
	+-------------^------------+		+-------------^------------+
	| | |		| | |
	-------------------+------|-----+-----+-------------+------		-------------------+------|-----+-----+-------------+------
	| ^ ^		| ^ ^
	Virtual IP --(VIPX)-+ (VIPX) (VIPX)		Virtual IP --(VIPX)-+ (VIPX) (VIPX)
	| |		| |
	+--+--+ +--+--+		+--+--+ +--+--+
	| H1 | | H2 |		| H1 | | H2 |
	+-----+ +-----+		+-----+ +-----+
	The above configuration shows the most likely utilization of the VRRP		Legend:
	protocol. In this configuration, the hosts simply point their default		---+---+---+-- = 802 network, Ethernet or FDDI
	routes at the virtual IP address X (VIPX), and the routers run VRRP
	between themselves. The router on the left is the default master
	router (MRX), and the router on the right is the backup router (BRX).
	Legend: ---+---+---+-- = 802 network, Ethernet or FDDI
	H = Host computer		H = Host computer
	MR = Master Router		MR = Master Router (Priority=200)
	BR = Backup Router		BR = Backup Router (Priority=100)
	* = IP Address		* = IP Address
	VIP = default gateway for hosts (Virtual IP)		VIP = default router for hosts (Virtual IP)
			The above configuration shows a typical VRRP scenario. In this
			configuration, the end-hosts install a default route to the virtual
			IP address (VIPX), and the routers run VRRP to elect the Master
			router. The router on the left (MRX) becomes the Master router
			because it has the highest priority and the router on the right (BRX)
			becomes the backup router.
	4.2 Sample Configuration 2		4.2 Sample Configuration 2
	The following figure shows a more interesting VRRP network.		The following figure shows a configuration with two clusters.
	+--------------------------+		+--------------------------+
	| Cluster X and Cluster Y |		| Cluster X and Cluster Y |
	| |		| |
	| +-----+ +-----+ |		| +-----+ +-----+ |
	| | MRX | | BRX | |		| | MRX | | BRX | |
	| | & | | & | |		| | & | | & | |
	| | BRY | | MRY | |		| | BRY | | MRY | |
	| +-----+ +-----+ |		| +-----+ +-----+ |
	Real IP 1 ---------->* *<---------- Real IP 2		Real IP 1 ---------->* *<---------- Real IP 2
	| | * * | |		| | * * | |
	+---------^------^---------+		+---------^------^---------+
	| | | |		| | | |
	------------------+--|------|--+-----+--------+--------+--------+--		------------------+--|------|--+-----+--------+--------+--------+--
	| | ^ ^ ^ ^		| | ^ ^ ^ ^
	Virtual IP --(VIPX)-+ | (VIPX) (VIPY) (VIPX) (VIPY)		Virtual IP --(VIPX)-+ | (VIPX) (VIPX) (VIPY) (VIPY)
	| | | | |		| | | | |
	Virtual IP --(VIPY)--------+ +--+--+ +--+--+ +--+--+ +--+--+		Virtual IP --(VIPY)--------+ +--+--+ +--+--+ +--+--+ +--+--+
	| H1 | | H2 | | H3 | | H4 |		| H1 | | H2 | | H3 | | H4 |
	+-----+ +-----+ +--+--+ +--+--+		+-----+ +-----+ +--+--+ +--+--+
	In the above configuration, half of the hosts point their default		Legend:
	gateway at cluster X's virtual IP address (VIPX), and half the hosts		---+---+---+-- = 802 network, Ethernet or FDDI
	point their default gateway at cluster Y's virtual IP address (VIPY).
	This has the effect of load balancing the outgoing traffic, while
	also providing full redundancy.
	Legend: ---+---+---+-- = 802 network, Ethernet or FDDI
	H = Host computer		H = Host computer
	MR = Master Router		MR = Master Router
	BR = Backup Router		BR = Backup Router
	* = IP Address		* = IP Address
	VIP = default gateway for hosts (Virtual IP)		VIP = default router for hosts (Virtual IP)
	5. Protocol		In the above configuration, half of the hosts install a default route
			to cluster X's virtual IP address (VIPX), and the other half of the
			hosts install a default route to cluster Y's virtual IP address
			(VIPY). This has the effect of load balancing the outgoing traffic,
			while also providing full redundancy.
	The purpose of the VRRP packet is to communicate to all other VRRP		5.0 Protocol
	routers both the priority and the state of the master's associated
	interface.		The purpose of the VRRP packet is to communicate to all VRRP routers
			the priority and the state of the Master router associated with the
			Virtual IP address.
	VRRP packets are sent encapsulated in IP packets. They are sent to		VRRP packets are sent encapsulated in IP packets. They are sent to
	an IPv4 multicast address assigned for VRRP.		an IPv4 multicast address assigned to VRRP.
	5.1 VRRP Packet Format		5.1 VRRP Packet Format
	This section defines the format of the VRRP packet and the relevant		This section defines the format of the VRRP packet and the relevant
	fields in the IP header.		fields in the IP header.
	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
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	0 | Version | VRRP Cluster | Priority | Type |		0 | Version | VRRP Cluster | Priority | Type |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	1 | Auth Type | Adver Int | Checksum |		1 | Auth Type | Adver Int | Checksum |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	2 | Virtual IP address |		2 | Virtual IP address |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	3 | Authentication Data |		3 | Authentication Data |
	+---------------------------------------------------------------+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	4 | |		4 | |
	+---------------------------------------------------------------+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	5.2 IP Field Descriptions		5.2 IP Field Descriptions
	5.2.1 Source Address		5.2.1 Source Address
	The real IP address of the interface the packet is being sent from.		The real IP address of the interface the packet is being sent from.
	5.2.2 Destination Address		5.2.2 Destination Address
	The VRRP IP multicast address assigned by the IANA. It is defined to		The VRRP IP multicast address assigned by the IANA. It is defined to
	be:		be:
	224.0.0.(TBD IANA assignment)		224.0.0.(TBD IANA assignment)
	This is a link local scope multicast address. Routers should not		This is a link local scope multicast address. Routers MUST NOT
	forward a datagram with this destination address regardless of its		forward a datagram with this destination address regardless of its
	TTL.		TTL.
	5.2.3 TTL		5.2.3 TTL
	The TTL should be set to 255. A VRRP router receiving a packet with		The TTL MUST be set to 255. A VRRP router receiving a packet with
	the TTL not equal to 255 MUST discard the packet.		the TTL not equal to 255 MUST discard the packet.
	5.2.4 Protocol		5.2.4 Protocol
	The VRRP IP protocol number assigned by the IANA. It is defined to		The VRRP IP protocol number assigned by the IANA. It is defined to
	be (TBD).		be (TBD).
	5.3 VRRP Field Descriptions		5.3 VRRP Field Descriptions
	5.3.1 Version		5.3.1 Version
	The version field specifies the VRRP protocol version of this packet.		The version field specifies the VRRP protocol version of this packet.
	This document defines version 1.		This document defines version 1.
	5.3.2 VRRP Cluster		5.3.2 VRRP Cluster
	The VRRP Cluster field specifies the cluster this packet applies to.		The VRRP Cluster field specifies the cluster this packet applies to.
	Note: The interface may participate in more than one VRRP cluster		Note: The interface may participate in more than one VRRP cluster
	simultaneously, perhaps serving as master in one cluster, while		simultaneously, perhaps serving as Master in one cluster, while
	simultaneously serving as backup in other clusters.		simultaneously serving as backup in other clusters.
	5.3.3 Priority		5.3.3 Priority
	The priority field specifies the currently configured VRRP priority		The priority field specifies the router's priority for the Virtual IP
	value for this interface and cluster. Higher values equal higher		address and cluster. Higher values equal higher priority. This
	priority. This field is an 8 bit unsigned field, giving 1 as the		field is an 8 bit unsigned field, giving 1 as the minimum priority,
	minimum priority, and 255 as the maximum priority. The default		and 255 as the maximum priority. The default priority is 100
	priority is 100 (decimal).		(decimal).
	Priority value of zero (0) has a special meaning. It means that the		The priority value zero (0) has special meaning indicating that the
	current master had decided to stop running VRRP. This is used to		current Master has stopped running VRRP. This is used to trigger
	cause other backup routers to quickly become master with out having		Backup routers to quickly transition to Master without having to wait
	to timeout the current master.		for the current Master to timeout.
	In the event that two or more routers within a cluster have equal		In the event that two or more routers within a cluster have equal
	priority, and that priority is the highest priority in the cluster,		priority, and that priority is the highest priority for the cluster,
	initially the router with the higher real interface IP address		initially the router with the higher real interface IP address
	(interpreted as a 32 bit unsigned integer) will become master. Any		(interpreted as a 32 bit unsigned integer) will become Master. Any
	new router joining the cluster with the same priority will not become		router joining the cluster with the same priority will not become
	master even if it has a higher IP address unless the current master		Master even if it has a higher IP address unless the current Master
	goes down.		goes down.
	5.3.4 Type		5.3.4 Type
	The type field specifies the type of this VRRP packet. The only		The type field specifies the type of this VRRP packet. The only
	packet type defined in this version of the protocol is:		packet type defined in this version of the protocol is:
	1 ADVERTISEMENT		1 ADVERTISEMENT
	All other values are currently unknown, and if a packet is received		A packet with unknown type MUST be discarded.
	with a value not listed, it should be discarded.
	5.3.5 Authentication Type		5.3.5 Authentication Type
	The authentication type field identifies the authentication method		The authentication type field identifies the authentication method
	being utilized. The current supported authentications are listed		being utilized. The authentication type field is an 8 bit number. A
	below:		packet with unknown authentication type or that does not match the
			locally configured authentication method MUST be discarded.
	0 - No authentication		The authentication methods currently defined are:
	1 - Simple text authentication
	2 - IP Security Option Authentication
	For simple text authentication any VRRP packet with an authentication		0 - No Authentication
	string that does not match its configured authentication string		1 - Simple Text Password
	should be discarded.		2 - IP Authentication Header
	The authentication type field is an 8 bit number and must be one of		5.3.5.1 No Authentication
	the above listed values.
	5.3.5.1 IP Security Option Authentication		The use of this authentication type means that VRRP protocol
			exchanges are not authenticated. The contents of the Authentication
			Data field should be set to zero on transmission and ignored on
			reception.
	When authentication is performed by using the IP Authentication		5.3.5.2 Simple Text Password
	Header as specified in [AUTH], the Authentication type should be set
	to "2". If packet is received with the Authentication type set to		The use of this authentication type means that VRRP protocol
	"2" indicating IP security option authentication and no		exchanges are authenticated by a clear text password. The contents
	authentication header is present in the packet, the packet should be		of the Authentication Data field should be set to the locally
	discarded.		configured password on transmission. There is no default password.
			The receiver MUST check that the Authentication Data in the packet
			matches its configured authentication string. Packets that do not
			match MUST be discarded.
			5.3.5.3 IP Authentication Header
			The use of this authentication type means the VRRP protocol exchanges
			are authenticated using the mechanisms defined by the IP
			Authentication Header [AUTH] using HMAC: Keyed-Hashing for Message
			Authentication [HMAC]. Keys may be either configured manually or via
			a key distribution protocol.
			If a packet is received that does not pass the authentication check
			due to a missing authentication header or incorrect message digest,
			then the packet MUST be discarded. The contents of the
			Authentication Data field should be set to zero on transmission and
			ignored on reception.
	5.3.6 Advertisement Interval (Adver Int)		5.3.6 Advertisement Interval (Adver Int)
	This field is the time interval for Master to Send ADVERTISEMENTS.		The Advertisement interval indicates the time interval (in seconds)
	Default is 1 second. This field is used for troubleshooting		between ADVERTISEMENTS. The default is 1 second. This field is used
	misconfigured routers.		for troubleshooting misconfigured routers.
	5.3.7 Checksum		5.3.7 Checksum
	The checksum field is used to detect data corruption in the VRRP		The checksum field is used to detect data corruption in the VRRP
	message.		message.
	The checksum is the 16-bit one's complement of the one's complement		The checksum is the 16-bit one's complement of the one's complement
	sum of the entire VRRP message starting with the version field. For		sum of the entire VRRP message starting with the version field. For
	computing the checksum, the checksum field is set to zero.		computing the checksum, the checksum field is set to zero.
	5.3.8 Virtual IP address		5.3.8 Virtual IP address
	The virtual IP address field specifies the Virtual IP (VIP) address		The virtual IP address field specifies the Virtual IP (VIP) address
	associated with the particular cluster. This field is used for		associated with the particular cluster. This field is used for
	troubleshooting misconfigured routers.		troubleshooting misconfigured routers.
	The VIP should be an IP address assigned from the subnet that the		The VIP MUST be an IP address assigned from the subnet that the
	interface is attached.		interface is attached and does not match any hosts real IP or cluster
			VIP address.
	5.3.9 Authentication Data		5.3.9 Authentication Data
	The authentication string is currently utilized for simple text		The authentication string is currently only utilized for simple text
	authentication, similar to the simple text authentication found in		authentication, similar to the simple text authentication found in
	OSPF. It is up to 8 characters of plain text. If the configured		the Open Shortest Path First routing protocol [OSPF]. It is up to 8
	authentication string is shorter than 8 bytes, the remaining space		characters of plain text. If the configured authentication string is
	MUST be zero-filled. Any VRRP packet with an authentication string		shorter than 8 bytes, the remaining space MUST be zero-filled. Any
	that does not match its configured authentication string should be		VRRP packet with an authentication string that does not match its
	discarded. The authentication string is unique on a per cluster		configured authentication string SHOULD be discarded. The
	basis.		authentication string is unique on a per interface basis.
			There is no default value for this field.
	6. Protocol State Machine		6. Protocol State Machine
	6.1 Parameters		6.1 Parameters
	Cluster_ID Cluster identifier. Configured item.		Cluster_ID Cluster identifier. Configured item. There
			is no default.
	Priority Priority value for this cluster. Configured		Priority Priority value for this cluster. Configured
	item. Default is 100 (decimal).		item. Range is between 1-255. Default is
			100 (decimal).
	Virtual_IP Virtual IP Address for this cluster.		Virtual_IP Virtual IP Address for this cluster.
	Configured item.		Configured item.
	Advertisement_Interval Time interval for Master to Send		Advertisement_Interval Time interval between ADVERTISEMENTS in
	ADVERTISEMENTS. Default is 1 second.		seconds. Default is 1 second.
	Skew_Time Calculated time to skew		Skew_Time Calculated time to skew Master_Down_Interval
	Master_Down_Interval. Defined to be:		in seconds. Defined to be:
	( (256 - Priority) / 256 )		( (256 - Priority) / 256 )
	Master_Down_Interval Time interval for Backup to declare Master		Master_Down_Interval Time interval for Backup to declare Master
	down. Defined to be:		down in seconds. Defined to be:
	(3 * Advertisement_Interval) + Skew_time		(3 * Advertisement_Interval) + Skew_time
	seconds.		Preempt_Mode Configuration switch controlling whether a
			higher priority VRRP router preempts a lower
			priority VRRP Master. Values are True to
			preempt and False to not preempt. Default
			is True.
	6.2 Timers		6.2 Timers
	Master_Down_Timer Timer which fires when Master has not been		Master_Down_Timer Timer that fires when ADVERTISEMENT has not
	heard for Master_Down_Interval.		been heard for Master_Down_Interval.
	Adver_Timer Timer which fires when time to send next		Adver_Timer Timer that fires to trigger sending of
	ADVERTISEMENT based on		ADVERTISEMENT based on
	Advertisement_Interval.		Advertisement_Interval.
	6.3 State Transition Diagram		6.3 State Transition Diagram
	+---------------+		+---------------+
	| |<-------------+		| |<-------------+
	+--------->| Initialize | |		+--------->| Initialize | |
	| | |----------+ |		| | |----------+ |
	| +---------------+ | |		| +---------------+ | |
	| | |		| | |
	| V |		| V |
	+---------------+ +---------------+		+---------------+ +---------------+
	| |---------------------->| |		| |---------------------->| |
	| Master | | Backup |		| Master | | Backup |
	| |<----------------------| |		| |<----------------------| |
	+---------------+ +---------------+		+---------------+ +---------------+
	6.4 State Descriptions		6.4 State Descriptions
	In the below state descriptions, the state names will be identified		In the state descriptions below, the state names are identified by
	as follows {state-name}, and the packets will be identified by		{state-name}, and the packets are identified by all upper case
	utilizing all upper case characters.		characters.
	6.4.1 Initialize		6.4.1 Initialize
	{Initialize} is the initial state an interface takes when VRRP is		{Initialize} is the state a virtual router takes when VRRP is
	enabled or disabled. The basic function of the state is to wait for		inactive. The purpose of this state is to wait for a Startup event.
	a startup event. When that is received it:		If a Startup event is received, then:
	- Set the Master_Down_Timer to Master_Down_Interval		- Set the Master_Down_Timer to Master_Down_Interval
	- Set state to {Backup} state.
			- Transition to the {Backup} state
	6.4.2 Backup		6.4.2 Backup
	The main purpose of {Backup} state is for an interface to wait for		The purpose of the {Backup} state is to monitor the availability and
	the current master to stop sending ADVERTISEMENT packets.		state of the Master Router.
	While in this state, an interface should do the following:		While in this state, an virtual router MUST do the following:
	- Should not respond to ARP request for the interface VIP router		- MUST NOT respond to ARP requests for the virtual router IP address
	address
	- Should discard packets with destination link layer MAC address		- MUST discard packets with a destination link layer MAC address
	equal to virtual router MAC.		equal to the virtual router MAC address
	- Should discard packets addressed to the interface VIP address.		- MUST not accept packets addressed to the Virtual IP address
			- If a Shutdown event is received, then:
	- If Master_Down_Timer fires, Send ADVERTISEMENT, set Adver_Timer		o Cancel the Master_Down_Timer
	to Advertisement_Interval, and set state to {Master} state		o Transition to the {Initialize} state
	- If ADVERTISEMENT received,		endif
	If Priority of the received ADVERTISEMENT is Zero, then set		- If the Master_Down_Timer fires, then:
	Mater_Down_Timer to Skew_Time.
	If Priority of the received ADVERTISEMENT is greater than		o Send an ADVERTISEMENT
	this interfaces Priority, then reset Master_Down_Timer.		o Set the Adver_Timer to Advertisement_Interval
			o Transition to the {Master} state
	If Priority of the received ADVERTISEMENT is equal to this		endif
	interfaces Priority, then reset Master_Down_Timer.
	If Priority of the received ADVERTISEMENT is lower than this		- If an ADVERTISEMENT is received, then:
	interfaces Priority, then discard ADVERTISEMENT.
			If the Priority in the ADVERTISEMENT is Zero, then:
			o Set the Master_Down_Timer to Skew_Time
			else:
			If Preempt_Mode is False, or If the Priority in the
			ADVERTISEMENT is greater than or equal to the local
			Priority, then:
			o Reset the Master_Down_Timer to Master_Down_Interval
			else:
			o Discard the ADVERTISEMENT
			endif
			endif
			endif
	6.4.3 Master		6.4.3 Master
	In {Master} state an interface is functioning as the actual physical		While in the {Master} state the router functions as the physical
	router for the virtual router IP and MAC address.		router for the Virtual IP address.
	While in this state, an interface should do the following:		While in this state, a virtual router MUST do the following:
	- Accept and forward traffic for the virtual router MAC address.		- MUST respond to ARP requests for the VIP address with the virtual
			router MAC address
			- Must accept and forward packets with a destination link layer MAC
			address equal to the virtual router MAC address
	- Respond to ARP requests for the VIP address with the virtual router		- Must accept packets addressed to the VIP address
	MAC address.
	- Respond to packets addressed to the VIP address.		- If a Shutdown event is received, then:
	- If Adver_Timer fires, send a ADVERTISEMENT and reset Adver_Timer.		o Cancel the Adver_Timer
			o Send an ADVERTISEMENT with Priority = 0
			o Transition to the {Initialize} state
	- If ADVERTISEMENT received,		endif
	If Priority of the received ADVERTISEMENT is higher than this		- If the Adver_Timer fires, then:
	interfaces Priority, then cancel Adver_Timer, Set
	Master_Down_Timer, and set state to {Backup}.
	If Priority of the received ADVERTISEMENT is equal to this		o Send an ADVERTISEMENT
	interfaces Priority, then:		o Reset the Adver_Timer to Advertisement_Interval
	If IP Address of sender of ADVERTISEMENT is higher than this		endif
	interfaces IP Address, then cancel Adver_Timer, Set
	Master_Down_Timer, and set state to {Backup}.
	If IP Address of sender of ADVERTISEMENT is lower than this		- If an ADVERTISEMENT is received, then:
	interfaces IP Address, discard ADVERTISEMENT.
	If Priority of the received ADVERTISEMENT is lower than this		If the Priority in the ADVERTISEMENT is Zero, then:
	interfaces Priority, discard ADVERTISEMENT.
	6.5 State Table		o Send an ADVERTISEMENT
			o Reset the Adver_Timer to Advertisement_Interval
	+---------------+---------------+---------------+---------------+		else:
	|Current State->| {Initialize} | {Backup} | {Master} |
	| | | | |		If the Priority in the ADVERTISEMENT is greater than the
	| Event | | | |		local Priority,
	| | | | | |		or
	| V | | | |		If the Priority in the ADVERTISEMENT is equal to the local
	+---------------+---------------+---------------+---------------+		Priority and the IP Address of the sender is greater than
	| | Set Master_ | | |		the local IP Address, then:
	| Startup | Down_Timer | | |
	| | State = | | |		o Cancel Adver_Timer
	| | Backup | | |		o Set Master_Down_Timer to Master_Down_Interval
	+---------------+---------------+---------------+---------------+		o Transition to the {Backup} state
	| | | Cancel Master_| Cancel Adver_ |
	| Shutdown | Ignore | Down_Timer | Timer |		else:
	| | Event | State = | Send ADVER w/ |
	| | | Initialize | Priority=0 |		o Discard ADVERTISEMENT
	| | | | State = Init. |
	+---------------+---------------+---------------+---------------+		endif
	| | | Send | |		endif
	| Master_Down_ | | ADVERTISEMENT| |		endif
	| Timer fires | | Set Adver_ | |
	| | | Timer | |
	| | | State = Master| |
	+---------------+---------------+---------------+---------------+
	| Adver_Timer | | | Send ADVER. |
	| fires | | | Reset Adver_ |
	| | | | Timer |
	+---------------+---------------+---------------+---------------+
	| Receive VRRP | | Set Master_ | Send ADVER. |
	| ADVERTISEMENT | | Down_Timer= | Reset Adver_ |
	| with Priority | | Skew_Timer | Timer |
	| equal Zero | | | |
	+---------------+---------------+---------------+---------------+
	| Receive VRRP | | | Cancel Adver_ |
	| ADVERTISEMENT | | Reset | Timer |
	| with Higher | | Master_Down_ | Set Master__ |
	| Priority | | Timer | Down_Timer |
	| | | | State = Backup|
	+---------------+---------------+---------------+---------------+
	| Receive VRRP | | | Cancel Adver_ |
	| ADVERTISEMENT | | Reset | Timer |
	| with Equal | | Master_Down_ | Set Master__ |
	| Priority | | Timer | Down_Timer |
	| and Higher IP | | | State = Backup|
	| Address | | | |
	+---------------+---------------+---------------+---------------+
	| Receive VRRP | | | |
	| ADVERTISEMENT | | Reset | Discard |
	| with Equal | | Master_Down | Packet |
	| Priority | | Timer | |
	| and Lower IP | | | |
	| Address | | | |
	+---------------+---------------+---------------+---------------+
	| Receive VRRP | | | |
	| ADVERTISEMENT | | Discard | Discard |
	| with Lower | | Packet | Packet |
	| Priority | | | |
	+---------------+---------------+---------------+---------------+
	| Receive ARP | | | Send ARP |
	| Request for | | Discard | Reply w/ |
	| VIP address | | Packet | VMAC |
	+---------------+---------------+---------------+---------------+
	| Receive IP | | | Process as |
	| packet w/ | | | Normal IP |
	| Destination | | | Packet sent |
	| = VIP | | | to Router |
	+---------------+---------------+---------------+---------------+
	| Receive IP | | | Process and |
	| packet w/ | | | Forward as |
	| Dest. MAC | | | Normal IP |
	| = VMAC | | | Packet |
	+---------------+---------------+---------------+---------------+
	| Unknown VRRP | | Discard | Discard |
	| packet | | Packet | Packet |
	+---------------+---------------+---------------+---------------+
	7. Sending and Receiving VRRP Packets		7. Sending and Receiving VRRP Packets
	7.1 Receiving VRRP Packets		7.1 Receiving VRRP Packets
	The following rules must be performed when a VRRP packet is received:		The following actions MUST be performed when a VRRP packet is
			received:
	- Verify TTL = 255.		- Verify that the IP TTL is 255.
	- Verify that received packet length is greater or equal to VRRP		- Verify that the received packet length is greater than or equal
	header length.		to the VRRP header length
	- Verify checksum in packet		- Verify the VRRP checksum
	- Verify version		- Verify the VRRP version
	- Verify Source address does not equal interface IP address		- Perform authentication specified by Auth Type
	- Verify Cluster identifier valid on received interface
	- Perform indicated authentication		If any one of the above checks fails, the receiver MUST discard the
	- Verify VIP in packet is same as configured VIP for this cluster		packet, SHOULD log the event and MAY indicate via network management
	- Verify Adver Interval in packet is same as configured VIP for		that an error occurred.
			- Verify that the Cluster identifier and the VIP are valid on the
			receiving interface
			- Verify that the VIP in packet is same as the configured VIP for
	this cluster		this cluster
	If one of these checks fails, the receiver should discard the packet,		If any one of the above checks fails, the receiver MUST discard the
	log the event and indicate via network management that an error		packet.
	occurred.
			- Verify that the Adver Interval in the packet is the same as the
			locally configured for this virtual router
			If the above check fails, the receiver MUST discard the packet,
			SHOULD log the event and MAY indicate via network management that an
			error occurred.
	7.2 Transmitting Packets		7.2 Transmitting Packets
	The following operations must be performed prior to transmitting a		The following operations MUST be performed prior to transmitting a
	VRRP packet.		VRRP packet.
	- Fill in packet fields with appropriate interface and cluster		- Fill in the VRRP packet fields with the appropriate virtual
	information		router configuration state
	- Compute Checksum		- Compute the VRRP checksum
	- Set source MAC to Virtual MAC Address		- Set the source MAC address to Virtual Router MAC Address
	- Send to VRRP IP Multicast Group		- Send the VRRP packet to the VRRP IP multicast group
	Note: VRRP packets are transmitted with the Virtual MAC address as		Note: VRRP packets are transmitted with the virtual MAC address as
	the source MAC to ensure that learning bridges correctly determine		the source MAC address to ensure that learning bridges correctly
	the LAN segment the virtual MAC is attached to.		determine the LAN segment the virtual router is attached to.
	7.3 Virtual MAC Address		7.3 Virtual Router MAC Address
	The default virtual MAC address associated with the virtual IP		The virtual router MAC address associated with a virtual router is an
	address is a IEEE 802 MAC Address of the following format:		IEEE 802 MAC Address in the following format:
	00-00-5E-XX-XX-{cluster id} (in hex in internet standard bit-order)		00-00-5E-XX-XX-{cluster id} (in hex in internet standard bit-order)
	The first three octets are the IANA's OUI. The next two octets (to		The first three octets are derived from the IANA's OUI. The next two
	be assigned by the IANA) indicate the address address block assigned		octets (to be assigned by the IANA) indicate the address block
	to the VRRP protocol. {cluster id} in the last octet is the VRRP		assigned to the VRRP protocol. {cluster id} is the VRRP cluster
	cluster identifier. This mapping allows for up to 255 VRRP clusters		identifier. This mapping provides for up to 255 VRRP clusters on a
	per interface.		network.
	Implementations may also allow Virtual MAC addresses to be configured
	for each cluster.
	8. Host Operation		8. Host Operation
	8.1 Host ARP Requests		8.1 Host ARP Requests
	When a client sends a ARP request for the virtual IP address, the		When a host sends an ARP request for the virtual IP address, the
	appropriate master router should respond to the ARP request with the		Master router MUST respond to the ARP request with the virtual MAC
	above virtual MAC address for the appropriate cluster. This allows		address for the virtual router. This allows the client to always use
	the client to always use the same MAC address regardless of the		the same MAC address regardless of the current Master router. The
	current master router. The request should be handled as a standard		request MUST be handled as a standard ARP reply.
	ARP reply.
	9. Operational Issues		9. Operational Issues
	9.1 ICMP Redirects		9.1 ICMP Redirects
	VRRP operation relies on the client host only using the Virtual IP		VRRP operation relies on hosts only using the Virtual IP address. It
	address and corresponding Virutal MAC. It is important that client		is important that client hosts do not learn the real IP address of
	hosts do not learn the real IP address of VRRP routers on LAN		any VRRP router on the LAN segment. Consequently VRRP routers MUST
	segment. Consequentially routers on the same LAN segment MUST NOT		NOT send ICMP Redirects on any interface they are running VRRP on.
	send ICMP Redirects with the real IP address of any VRRP routers.
	9.2 Proxy ARP		9.2 Proxy ARP
	If Proxy ARP is being used on routers running VRRP, the VRRP routers		If Proxy ARP is to be used on a router running VRRP, then the VRRP
	must advertise the Virtual MAC address in the Proxy ARP message.		router must advertise the Virtual Router MAC address in the Proxy ARP
	Doing otherwise would cause them to learn the real IP address of the		message. Doing otherwise could cause hosts to learn the real IP
	VRRP routers.		address of the VRRP routers.
	9.3 Network Management		9.3 Network Management
	It is important that network management tools (e.g., SNMP, Telnet,		It is important that network management tools (e.g., SNMP, Telnet,
	etc.) always use the real IP addresses of VRRP routers. This is		etc.) always use the real IP addresses of a VRRP router. This
	necessary to insure that network management is aware of the real		ensures that network management is aware of the status of the real
	status of the VRRP routers (e.g., detect that a router has failed so		routers (e.g., to detect that a router has failed so that it can be
	that it can be repaired).		repaired).
	10. Operation over Token Ring		10. Operation over FDDI and Token Ring
	TBD		10.1 Operation over FDDI
	11. References		FDDI interfaces strip from the FDDI ring frames that have a source
			MAC address matching the device's hardware address. Under some
			conditions, such as router isolations, ring failures, protocol
			transitions, etc., VRRP may cause there to be more than one Master
			router. If a Master router installs the virtual router MAC address
			as the hardware address on a FDDI device, then other Masters'
			ADVERTISEMENTS will be stripped off the ring during the Master
			convergence, and convergence will fail.
	[AUTH] Atkinson, R., "IP Authentication Header", RFC 1826, Naval		To avoid this an implementations SHOULD configure the virtual router
	Research Laboratory, August 1995.		MAC address by adding a unicast MAC filter in the FDDI device, rather
			than changing its hardware MAC address. This will prevent a Master
			router from stripping any ADVERTISEMENTS it did not originate.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		10.2 Operation over Token Ring
	Requirement Levels", RFC2119, BCP14, March 1997.
	12. Security Considerations		Token Ring has several characteristics which make running VRRP
			problematic. This includes:
	The protocol design supports no authentication, simple text		- No general multicast mechanism. Required use of "functional
	authentication, and integrity/authentication/integrity using the IP		addresses" as a substitute, which may collide with other usage of
	Security options.		the same "functional addresses".
			- Token Ring interfaces may have a limited ability to receive on
			multiple MAC addresses.
			- In order to switch to a new master located on a different physical
			ring from the previous master when using source route bridges, a
			mechanism is required to update cached source route information.
			Due the these issues and the limited knowledge about the detailed
			operation of Token Ring by the authors, this version of VRRP does not
			work over Token Ring networks. This may be remedied in new version
			of this document, or in a separate document.
			11. Security Considerations
			VRRP is designed for a range of internetworking environments that may
			employ different security policies. The protocol includes several
			authentication methods ranging from no authentication, simple clear
			text passwords, and strong authentication using IP Authentication
			with HMAC. The details on each approach including possible attacks
			and recommended environments follows.
			Independent of any authentication type VRRP includes a mechanism
			(setting TTL=255, checking on receipt) that protects against VRRP
			packets being injected from another remote network. This limits most
			vulnerabilities to local attacks.
			11.1 No Authentication
			The use of this authentication type means that VRRP protocol
			exchanges are not authenticated. This type of authentication SHOULD
			only be used in environments were there is minimal security risk and
			little chance for configuration errors (e.g., two VRRP routers in a
			single cluster on a link).
			11.2 Simple Text Password
			The use of this authentication type means that VRRP protocol
			exchanges are authenticated by a simple clear text password.
			This type of authentication is useful to protect against accidental
			misconfiguration of routers on a link. It protects against routers
			inadvertently becoming a member of a VRRP cluster. A new router must
			first be configured with the correct password before it can become a
			member of the VRRP cluster. This type of authentication does not
			protect against hostile attacks where the password can be learned by
			a node snooping VRRP packets on the link. The Simple Text
			Authentication combined with the TTL check makes it difficult for a
			VRRP packet to be sent from another link to disrupt VRRP operation.
			This type of authentication is RECOMMENDED when there is minimal risk
			of nodes on the link actively disrupting VRRP operation.
			11.3 IP Authentication Header
			The use of this authentication type means the VRRP protocol exchanges
			are authenticated using the mechanisms defined by the IP
			Authentication Header [AUTH] using HMAC: Keyed-Hashing for Message
			Authentication [HMAC]. This provides strong protection against
			configuration errors, replay attacks, and packet
			corruption/modification.
			This type of authentication is RECOMMENDED when there is limited
			control over the administration of nodes on the link. While this
			type of authentication does protect the operation of VRRP, there are
			other types of attacks that may be employed on shared media links
			(e.g., generation of bogus ARP replies) which are independent from
			VRRP and are not protected.
			12. References
			[AUTH] Atkinson, R., "IP Authentication Header", RFC-1826, August
			1995.
			[DISC] Deering, S., "ICMP Router Discovery Messages", RFC-1256,
			September 1991.
			[DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC-1541,
			October 1993.
			[HMAC] Krawczyk, H., M. Bellare, R. Canetti, "HMAC: Keyed-Hashing
			for Message Authentication", RFC-2104, February 1997.
			[HSRP] Li, T., B. Cole, P. Morton, D. Li, "Hot Standby Router
			Protocol (HSRP)", Internet Draft, <draft-li-hsrp-00.txt>,
			June 1997.
			[OSPF] Moy, J., "OSPF version 2", RFC-1583, July 1997.
			[RIP] Hedrick, C., "Routing Information Protocol" , RFC-1058,
			June 1988.
			[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
			Requirement Levels", RFC-2119, BCP14, March 1997.
	13. Author's Addresses		13. Author's Addresses
	Steven Knight Phone: +1 612 943-8990		Steven Knight Phone: +1 612 943-8990
	Ascend Communications EMail: Steven.Knight@ascend.com		Ascend Communications EMail: Steven.Knight@ascend.com
	High Performance Network Division		High Performance Network Division
	10250 Valley View Road, Suite 113		10250 Valley View Road, Suite 113
	Eden Prairie, MN USA 55344		Eden Prairie, MN USA 55344
			USA
	Douglas Weaver Phone: +1 612 943-8990		Douglas Weaver Phone: +1 612 943-8990
	Ascend Communications EMail: Doug.Weaver@ascend.com		Ascend Communications EMail: Doug.Weaver@ascend.com
	High Performance Network Division		High Performance Network Division
	10250 Valley View Road, Suite 113		10250 Valley View Road, Suite 113
	Eden Prairie, MN USA 55344		Eden Prairie, MN USA 55344
			USA
	David Whipple Phone: +1 206 703-3876		David Whipple Phone: +1 206 703-3876
	Microsoft Corporation EMail: dwhipple@microsoft.com		Microsoft Corporation EMail: dwhipple@microsoft.com
	One Microsoft Way		One Microsoft Way
	Redmond, WA USA 98052-6399		Redmond, WA USA 98052-6399
			USA
	Robert Hinden Phone: +1 408 990-2004		Robert Hinden Phone: +1 408 990-2004
	Ipsilon Networks, Inc. EMail: hinden@ipsilon.com		Ipsilon Networks, Inc. EMail: hinden@ipsilon.com
	232 Java Drive		232 Java Drive
	Sunnyvale, CA 94089		Sunnyvale, CA 94089
			USA
			Danny Mitzel Phone: +1 408 990-2037
			Ipsilon Networks, Inc. EMail: mitzel@ipsilon.com
			232 Java Drive
			Sunnyvale, CA 94089
			USA
	14. Acknowledgments		14. Acknowledgments
	The authors would like to thank Glen Zorn, and Michael Lane, Clark		The authors would like to thank Glen Zorn, and Michael Lane, Clark
	Bremer, Hal Peterson, Danny Mitzel, and Peter Hunt for their comments		Bremer, Hal Peterson, Peter Hunt, Tony Li, Barbara Denny, and Steve
	and suggestions.		Bellovin for their comments and suggestions.
	15. Changes from Previous Drafts		15. Changes from Previous Drafts
			Changes from <draft-ietf-vrrp-spec-00.txt>
			- Added Preempt_Mode to allow user control over preemption
			independent of configured priorities.
			- Rewrote authentication section and expanded security
			considerations.
			- Expanded State Description section and removed State Table which
			become redundant and impossible to edit.
			- Changed authentication to be on a per interface basis (not per
			cluster).
			- Clarified text on disabling ICMP Redirects.
			- Added text on FDDI and Token Ring issues.
			- Added HSRP acknowledgment.
			- Rewrote Introduction, Required Features, and VRRP Overview
			sections.
			- Many small text clarifications.
	Changes from <draft-hinden-vrrp-00.txt>		Changes from <draft-hinden-vrrp-00.txt>
	- Changed default behavior to stay with current master when		- Changed default behavior to stay with current master when
	priorities are equal. This behavior can be changed by configuring		priorities are equal. This behavior can be changed by configuring
	explicit priorities.		explicit priorities.
	- Changed Master state behavior to not send Advertisements when		- Changed Master state behavior to not send Advertisements when
	receiving Advertisement with lower priorty. Change reduces worst		receiving Advertisement with lower priority. Change reduces worst
	case election message overhead to "n", where "n" is number of		case election message overhead to "n", where "n" is number of
	configured equal priority VRRP routers.		configured equal priority VRRP routers.
	- Added Skew_Time parameter and changed receiving advertisement with		- Added Skew_Time parameter and changed receiving advertisement with
	zero priority behavior to cause resulting advertisement sent to be		zero priority behavior to cause resulting advertisement sent to be
	skewed by priority.		skewed by priority.
	- Changed sending behavior to send VRRP packets with VMAC as source		- Changed sending behavior to send VRRP packets with VMAC as source
	MAC and added text describing why this is important for bridged		MAC and added text describing why this is important for bridged
	environments.		environments.
	- Changed definition of VMAC to be in IANA assigned unicast MAC		- Changed definition of VMAC to be in IANA assigned unicast MAC
	block.		block.
	- Added Advertisement Interval to VRRP header.		- Added Advertisement Interval to VRRP header.
	- Added text regarding ICMP Redirects, Proxy ARP, and network		- Added text regarding ICMP Redirects, Proxy ARP, and network
	management issues.		management issues.
	- Various small text clarifications.		- Various small text clarifications.
End of changes.
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