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rfc:rfc2281

Network Working Group T. Li Request for Comments: 2281 Juniper Networks Category: Informational B. Cole

                                                      Juniper Networks
                                                             P. Morton
                                                         Cisco Systems
                                                                 D. Li
                                                         Cisco Systems
                                                            March 1998
              Cisco Hot Standby Router Protocol (HSRP)

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (1998).  All Rights Reserved.

IESG Note

 This document reflects an existing deployed protocol.  The IETF does
 have a working group which is in the process of producing a standards
 track protocol to address the same issues.

Abstract

 The memo specifies the Hot Standby Router Protocol (HSRP).  The goal
 of the protocol is to allow hosts to appear to use a single router
 and to maintain connectivity even if the actual first hop router they
 are using fails.  Multiple routers participate in this protocol and
 in concert create the illusion of a single virtual router.  The
 protocol insures that one and only one of the routers is forwarding
 packets on behalf of the virtual router.  End hosts forward their
 packets to the virtual router.
 The router forwarding packets is known as the active router.  A
 standby router is selected to replace the active router should it
 fail. The protocol provides a mechanism for determining active and
 standby routers, using the IP addresses on the participating routers.
 If an active router fails a standby router can take over without a
 major interruption in the host's connectivity.  This memo also
 discusses the ARP, MAC address, and security issues with this
 protocol.

Li, et. al. Informational [Page 1] RFC 2281 Cisco HSRP March 1998

TABLE OF CONTENTS

 1   Introduction ..............................................  2
 2   Conditions of Use .........................................  3
 3   Scope .....................................................  4
 3.1 Terminology ...............................................  4
 4   Definitions ...............................................  4
 5   Protocol ..................................................  4
 5.1 Packet formats ............................................  4
 5.2 Operational parameters ....................................  7
 5.3 States ....................................................  8
 5.4 Timers ....................................................  9
 5.5 Events ....................................................  9
 5.6 Actions ................................................... 10
 5.7 State Transitions.......................................... 11
 6   MAC address considerations ................................ 13
 6.1 General ................................................... 13
 6.2 Address Filter ............................................ 14
 6.3 ICMP Redirect ............................................. 14
 6.4 Proxy ARP ................................................. 15
 7   Security Considerations ................................... 15
 8   References ................................................ 15
 9   Authors' Addresses ........................................ 16
 10  Full Copyright Statement .................................. 17

1. Introduction

 The Hot Standby Router Protocol, HSRP, provides a mechanism which is
 designed to support non-disruptive failover of IP traffic in certain
 circumstances.  In particular, the protocol protects against the
 failure of the first hop router when the source host cannot learn the
 IP address of the first hop router dynamically.  The protocol is
 designed for use over multi-access, multicast or broadcast capable
 LANs (e.g., Ethernet).  HSRP is not intended as a replacement for
 existing dynamic router discovery mechanisms and those protocols
 should be used instead whenever possible [1].  A large class of
 legacy host implementations that do not support dynamic discovery are
 capable of configuring a default router.  HSRP provides failover
 services to those hosts.
 All of the routers participating in HSRP are assumed to be running
 appropriate IP routing protocols and have a consistent set of routes.
 The discussion of which protocols are appropriate and whether routing
 is consistent in any given situation is beyond the scope of this
 specification.

Li, et. al. Informational [Page 2] RFC 2281 Cisco HSRP March 1998

 Using HSRP, a set of routers work in concert to present the illusion
 of a single virtual router to the hosts on the LAN.  This set is
 known as an HSRP group or a standby group.  A single router elected
 from the group is responsible for forwarding the packets that hosts
 send to the virtual router.  This router is known as the active
 router.  Another router is elected as the standby router.  In the
 event that the active router fails, the standby assumes the packet
 forwarding duties of the active router.  Although an arbitrary number
 of routers may run HSRP, only the active router forwards the packets
 sent to the virtual router.
 To minimize network traffic, only the active and the standby routers
 send periodic HSRP messages once the protocol has completed the
 election process.  If the active router fails, the standby router
 takes over as the active router.  If the standby router fails or
 becomes the active router, another router is elected as the standby
 router.
 On a particular LAN, multiple hot standby groups may coexist and
 overlap.  Each standby group emulates a single virtual router.  For
 each standby group, a single well-known MAC address is allocated to
 the group, as well as an IP address.  The IP address SHOULD belong to
 the primary subnet in use on the LAN, but MUST differ from the
 addresses allocated as interface addresses on all routers and hosts
 on the LAN, including virtual IP addresses assigned to other HSRP
 groups.
 If multiple groups are used on a single LAN, load splitting can be
 achieved by distributing hosts among different standby groups.
 The remainder of this specification discusses the operation of a
 single standby group.  In the case of multiple groups, each group
 operates independently of other groups on the LAN and according to
 this specification.  Note that individual routers may participate in
 multiple groups.  In this case, the router maintains separate state
 and timers for each group.

2 Conditions of Use

 US Patent number 5,473,599 [2], assigned to Cisco Systems, Inc. may
 be applicable to HSRP.  If an implementation requires the use of any
 claims of patent no. 5,473,599, Cisco will license such claims on
 reasonable, nondiscriminatory terms for use in practicing the
 standard.  More specifically, such license will be available for a
 one-time, paid up fee.

Li, et. al. Informational [Page 3] RFC 2281 Cisco HSRP March 1998

3 Scope

 This document describes the packets, messages, states, and events
 used to implement the protocol.  It does not discuss network
 management or internal implementation issues.

3.1 Terminology

 The language conventions of RFC 2119 [3] are used in this document.

4 Definitions

 Active Router   - the router that is currently forwarding packets
                   for the virtual router
 Standby Router  - the primary backup router
 Standby Group   - the set of routers participating in HSRP that
                   jointly emulate a virtual router
 Hello Time      - the interval between successive HSRP Hello
                   messages from a given router
 Hold Time       - the interval between the receipt of a Hello
                   message and the presumption that the sending
                   router has failed

5 Protocol

 Within a standby group, the routers periodically advertise state
 information using various messages.

5.1 Packet formats

 The standby protocol runs on top of UDP, and uses port number 1985.
 Packets are sent to multicast address 224.0.0.2 with TTL 1.
 Routers use their actual IP address as the source address for
 protocol packets, not the virtual IP address.  This is necessary so
 that the HSRP routers can identify each other.
 The format of the data portion of the UDP datagram is:

Li, et. al. Informational [Page 4] RFC 2281 Cisco HSRP March 1998

                        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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Version     |   Op Code     |     State     |   Hellotime   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Holdtime    |   Priority    |     Group     |   Reserved    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      Authentication  Data                     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      Authentication  Data                     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      Virtual IP Address                       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Version:  1 octet
    The version of the HSRP messages.  This document describes version
    0.
 Op Code:  1 octet
    The Op Code describes the type of message contained in this
    packet.  Possible values are:
       0 - Hello
       1 - Coup
       2 - Resign
    Hello messages are sent to indicate that a router is running and
    is capable of becoming the active or standby router.
    Coup messages are sent when a router wishes to become the active
    router.
    Resign messages are sent when a router no longer wishes to be the
    active router.
 State:  1 octet
    Internally, each router in the standby group implements a state
    machine.  The State field describes the current state of the
    router sending the message.  Details on the individual states are
    described below.  Possible values are:

Li, et. al. Informational [Page 5] RFC 2281 Cisco HSRP March 1998

       0 - Initial
       1 - Learn
       2 - Listen
       4 - Speak
       8 - Standby
      16 - Active
 Hellotime:  1 octet
    This field is only meaningful in Hello messages.  It contains the
    approximate period between the Hello messages that the router
    sends.  The time is given in seconds.
    If the Hellotime is not configured on a router, then it MAY be
    learned from the Hello message from the active router.  The
    Hellotime SHOULD only be learned if no Hellotime is configured and
    the Hello message is authenticated.  A router that sends a Hello
    message MUST insert the Hellotime that it is using in the
    Hellotime field in the Hello message.  If the Hellotime is not
    learned from a Hello message from the active router and it is not
    manually configured, a default value of 3 seconds is RECOMMENDED.
 Holdtime:  1 octet
    This field is only meaningful in Hello messages.  It contains the
    amount of time that the current Hello message should be considered
    valid.  The time is given in seconds.
    If a router sends a Hello message, then receivers should consider
    that Hello message to be valid for one Holdtime.  The Holdtime
    SHOULD be at least three times the value of the Hellotime and MUST
    be greater than the Hellotime.  If the Holdtime is not configured
    on a router, then it MAY be learned from the Hello message from
    the active router.  The Holdtime SHOULD only be learned if the
    Hello message is authenticated.  A router that sends a Hello
    message MUST insert the Holdtime that it is using in the Holdtime
    field in the Hello message.
    A router which is in active state MUST NOT learn new values for
    the Hellotime and the Holdtime from other routers, although it may
    continue to use values which it learned from the previous active
    router.  It MAY also use the Hellotime and Holdtime values learned
    through manual configuration.  The active router MUST NOT use one
    configured time and one learned time.  If the Holdtime is not
    learned and it is not manually configured, a default value of 10
    seconds is RECOMMENDED.

Li, et. al. Informational [Page 6] RFC 2281 Cisco HSRP March 1998

 Priority:  1 octet
    This field is used to elect the active and standby routers.  When
    comparing priorities of two different routers, the router with the
    numerically higher priority wins.  In the case of routers with
    equal priority the router with the higher IP address wins.
 Group:   1 octet
    This field identifies the standby group.  For Token Ring, values
    between 0 and 2 inclusive are valid.  For other media values
    between 0 and 255 inclusive are valid.
 Authentication Data:    8 octets
    This field contains a clear-text 8 character reused password.
    If no authentication data is configured, the RECOMMENDED default
    value is 0x63 0x69 0x73 0x63 0x6F 0x00 0x00 0x00.
 Virtual IP Address:     4 octets
    The virtual IP address used by this group.
    If the virtual IP address is not configured on a router, then it
    MAY be learned from the Hello message from the active router.  An
    address SHOULD only be learned if no address was configured and
    the Hello message is authenticated.

5.2 Operational parameters

 The following information MUST be known to each router in the standby
 group.  The mechanisms used to determine this information are outside
 of the scope of this document.
    Standby group number
    Virtual MAC address
    Priority
    Authentication Data
    Hellotime
    Holdtime

Li, et. al. Informational [Page 7] RFC 2281 Cisco HSRP March 1998

 The following information MUST be known to at least one router in
 each standby group and MAY be known by any of the other routers in
 the group.
    Virtual IP Address
 The following information MAY be configured on any router:
    Preemption capability
       If a router has higher priority than the active router and
       preemption is configured, it MAY take over as the active router
       using a Coup message.

5.3 States

 Each router in the group participates in the protocol by implementing
 a simple state machine.  This specification describes the externally
 visible behavior of this state machine.  Implementations MAY vary
 their internal implementations within the functional description of
 the state machine.
 All routers begin in the Initial state.  This section discusses the
 intent of each state.  For specific details on the actions taken in
 each state, please see the state transition table in section 5.7.
 1. Initial
    This is the starting state and indicates that HSRP is not running.
    This state is entered via a configuration change or when an
    interface first comes up.
 2. Learn
    The router has not determined the virtual IP address, and not yet
    seen an authenticated Hello message from the active router.  In
    this state the router is still waiting to hear from the active
    router.
 3. Listen
    The router knows the virtual IP address, but is neither the active
    router nor the standby router.  It listens for Hello messages from
    those routers.

Li, et. al. Informational [Page 8] RFC 2281 Cisco HSRP March 1998

 4. Speak
    The router sends periodic Hello messages and is actively
    participating in the election of the active and/or standby router.
    A router cannot enter Speak state unless it has the virtual IP
    address.
 5. Standby
    The router is a candidate to become the next active router and
    sends periodic Hello messages.  Excluding transient conditions,
    there MUST be at most one router in the group in Standby state.
 6. Active
    The router is currently forwarding packets that are sent to the
    group's virtual MAC address.  The router sends periodic Hello
    messages.  Excluding transient conditions, there MUST be at most
    one router in Active state in the group.

5.4 Timers

 Each router maintains three timers, an Active timer, a Standby timer,
 and a Hello timer.
 The Active timer is used to monitor the active router.  The active
 timer is started anytime an authenticated Hello message is seen from
 the active router.  It is set to expire in the Holdtime seen in the
 Hello message.
 The Standby timer is used to monitor the standby router The Standby
 timer is started anytime an authenticated Hello message is seen from
 the standby router.  It is set to expire in the Holdtime seen in the
 Hello message.
 The Hello timer expires once per Hellotime period.  If the router is
 in Speak, Standby, or Active states, it should generate a Hello
 message upon Hello timer expiry.  The Hello timer MUST be jittered.

5.5 Events

 These are the events in the HSRP finite state machine.
    a - HSRP is configured on an enabled interface.
    b - HSRP is disabled on an interface or the interface is disabled.

Li, et. al. Informational [Page 9] RFC 2281 Cisco HSRP March 1998

    c - Active timer expiry.  The Active timer was set to the Holdtime
    when the last Hello message was seen from the active router.
    d - Standby timer expiry.  The Standby timer was set to the
    Holdtime when the last Hello message was seen from the standby
    router.
    e - Hello timer expiry.  The periodic timer for sending Hello
    messages has expired.
    f - Receipt of a Hello message of higher priority from a router in
    Speak state.
    g - Receipt of a Hello message of higher priority from the active
    router.
    h - Receipt of a Hello message of lower priority from the active
    router.
    i - Receipt of a Resign message from the active router.
    j - Receipt of a Coup message from a higher priority router.
    k - Receipt of a Hello message of higher priority from the standby
    router.
    l - Receipt of a Hello message of lower priority from the standby
    router.

5.6 Actions

 This section specifies the actions to be taken as part of the state
 machine.
    A  Start Active Timer
       If this action occurred as the result of the receipt of a an
       authenticated Hello message from the active router, the Active
       timer is set to the Holdtime field in the Hello message.
       Otherwise the Active timer is set to the current Holdtime value
       in use by this router.  The Active timer is then started.
    B  Start Standby Timer
       If this action occurred as the result of the receipt of an
       authenticated Hello message from the standby router, the
       Standby timer is set to the Holdtime field in the Hello
       message.  Otherwise the Standby timer is set to the current
       hold time value in use by this router.  The Standby timer is
       then started.

Li, et. al. Informational [Page 10] RFC 2281 Cisco HSRP March 1998

    C  Stop Active Timer
       The Active timer is stopped.
    D  Stop Standby Timer
       The Standby timer is stopped.
    E  Learn Parameters
       This action is taken when an authenticated message is received
       from the active router.  If the virtual IP address for this
       group was not manually configured, the virtual IP address MAY
       be learned from the message.  The router MAY learn Hellotime
       and Holdtime values from the message.
    F  Send Hello Message
       The router sends a Hello message with its current State,
       Hellotime and Holdtime.
    G  Send Coup Message
       The router sends a Coup message to inform the active router
       that there is a higher priority router available.
    H  Send Resign Message
       The router sends a Resign message to allow another router to
       become the active router.
    I  Send Gratuitous ARP Message
       The router broadcasts an ARP response packet advertising the
       group's virtual IP address and virtual MAC address.  The packet
       is sent using the virtual MAC address as the source MAC address
       in the link layer header, as well as within the ARP packet.

5.7 State Transitions

 This table describes the state transitions of the state machine.  For
 each event and current state of the router, the router MUST perform
 the set of actions specified and transition to the designated state.
 If no action is specified, no action should be taken.  If no state
 change is specified, no state change should be performed.
 The notation used in this table has the specified set of actions
 listed as letters corresponding to the actions listed in section 5.6.
 The next state is listed as a number as specified in section 5.3.  A
 slash ('/') separates the actions and states.  Certain state
 transitions have alternatives which depend on external state.
 Alternatives are separated by a '|'.  See the attached notes for
 details on these transitions.

Li, et. al. Informational [Page 11] RFC 2281 Cisco HSRP March 1998

                                               States

+—–+———-+———-+———-+———-+———-+———-+

1 2 3 4 5 6
Initial Learn Listen Speak Standby Active

+—–+———-+———-+———-+———-+———-+———-+

Event

+—–+———-+———-+———-+———-+———-+———-+

a AB/23+

+—–+———-+———-+———-+———-+———-+———-+

b CD/1 CD/1 CD/1 CD/1 CDH/1

+—–+———-+———-+———-+———-+———-+———-+

c AB/4 CDFI/6

+—–+———-+———-+———-+———-+———-+———-+

d B/4 D/5

+—–+———-+———-+———-+———-+———-+———-+

e F F F

+—–+———-+———-+———-+———-+———-+———-+

f B/3 B/3

+—–+———-+———-+———-+———-+———-+———-+

g EAB/3 EA EA EA AB/4

+—–+———-+———-+———-+———-+———-+———-+

h EAB/3 ABGFI/6* ABGFI/6* ABGFI/6* G

+—–+———-+———-+———-+———-+———-+———-+

i AB/4 A CFI/6

+—–+———-+———-+———-+———-+———-+———-+

j ABH/4

+—–+———-+———-+———-+———-+———-+———-+

k B B/3 B/3 B

+—–+———-+———-+———-+———-+———-+———-+

l B/4 D/5 B

+—–+———-+———-+———-+———-+———-+———-+

 Notes
 +   If the virtual IP address is configured, set state 3 (Listen) If
 the virtual IP address is not configured, set state 2 (Learn).  In
 either case do actions A and B.
  • If the router is configured to preempt do actions B, G, F, and I

and set state to 6 (Active). If the router is not configured to

 preempt do actions A with no state change.

Li, et. al. Informational [Page 12] RFC 2281 Cisco HSRP March 1998

6 MAC Address Considerations

6.1 General

 Each HSRP group has an associated well known virtual MAC address.  On
 token ring networks, these addresses are actually functional
 addresses.  The three addresses 0xC0 0x00 0x00 0x01 0x00 0x00, 0xC0
 0x00 0x00 0x02 0x00 0x00, and 0xC0 0x00 0x00 0x04 0x00 0x00
 correspond to groups 0, 1, and 2 respectively.
 On other media, the virtual MAC addresses are 0x00 0x00 0x0C 0x07
 0xAC XX where XX represents the HSRP group number.  Routers which
 implement HSRP SHOULD use well-known HSRP MAC addresses as the
 group's virtual MAC address whenever possible.
 The active router MUST accept and forward traffic that is destined
 for the group's virtual MAC address.  It MUST stop accepting or
 forwarding such traffic when the router leaves the Active state.
 If and only if the router is in the Active state, the router MUST use
 the group's virtual MAC address as the source MAC address for its
 Hello messages.  This is necessary in order to allow learning bridges
 to be able to determine which LAN segment the virtual MAC address
 currently belongs to.
 For each group, there is one virtual IP address and one virtual MAC
 address.  This is a desirable situation, since the ARP table entries
 in the end stations do not need to change over time as the HSRP
 active router moves from one router to another.
 Additionally, for HSRP to work in bridging environments, the bridges
 must be able to quickly update themselves as the virtual MAC address
 "moves".  Although learning bridges typically are able to do this,
 some have been known to have problems with this.  It is RECOMMENDED
 that only true learning bridges be used with HSRP.
 The movement of the virtual MAC address can cause further undesirable
 side effects in environments where additional state is tied to the
 MAC address.  For example on Token Ring, if Source Route Bridging is
 in use, a RIF will be stored with the virtual MAC address in a host's
 RIF cache.  The RIF indicates the path and final ring used to reach
 the MAC address.  As routers transition into Active state, they will
 not be able to affect the RIF caches on the hosts on the bridged
 ring.  This may lead to packets being bridged to the ring for the
 previous active router.

Li, et. al. Informational [Page 13] RFC 2281 Cisco HSRP March 1998

 In such circumstances, a router MAY use its normal MAC addresses as
 the virtual MAC address.  This method of operation is strongly
 discouraged.  In this mode, the virtual IP address will map to a
 different MAC address over time.  This can create problems for end
 stations, since ARP tables assume a relatively static mapping between
 MAC address and IP address.  These ARP tables are normally updated
 when the end stations receive the gratuitous ARP responses generated
 by a router that enters the active state.

6.2 Address Filter

 As noted, routers currently emulating a virtual router adopt their
 group's MAC and IP addresses.  MAC addresses are typically provided
 in an address filter or 'list' of MAC addresses in a router's
 interface controller.  It is desirable for routers to be able to add
 one or more virtual MAC addresses to their controllers' MAC address
 filter while maintaining their primary MAC addresses.
 Unfortunately, some interface controllers support address filtering
 for only one unicast MAC address.  Or, in the case of Token Ring, the
 functional address which HSRP should use is already in use for some
 other protocol.  In these cases, such routers can still implement
 HSRP, but the protocol must change the interface's primary MAC
 address when assuming or relinquishing control as the active router.
 This is potentially problematic because some traffic may otherwise
 wish to use the router's primary MAC address.  However, the problem
 MAY be mitigated by having the router send out gratuitous ARP packets
 regarding its non-HSRP IP addresses.  Through this, other network
 entities using IP should update their ARP tables to reflect that the
 router is now using a group virtual MAC address rather than its
 primary MAC address.
 Some protocols may not be able to run simultaneously with the standby
 protocol due to the interface primary MAC address change.  For
 example, DECnet phase IV and HSRP will not be able to run at the same
 time on some equipment.

6.3 ICMP Redirect

 While running HSRP, it is important to prevent the host from
 discovering the primary MAC addresses of the routers in its standby
 group.  Thus, any protocol that informs a host of a router's primary
 address should be disabled.  Thus, routers participating in HSRP on
 an interface MUST NOT send ICMP redirects on that interface.

Li, et. al. Informational [Page 14] RFC 2281 Cisco HSRP March 1998

6.4 Proxy ARP

 Typically, hosts learn the HSRP virtual IP address through the
 configuration of their default router.  These hosts then send packets
 for destinations outside of the LAN to the virtual IP address.  In
 some environments, hosts may instead make use of proxy ARP in order
 to route off of the LAN.  In this case, the hosts use the MAC address
 that is supplied in proxy ARP responses.  HSRP functionality is
 maintained if the proxy ARP responses specify the HSRP virtual MAC
 address.
 If an HSRP router is configured to support proxy ARP with HSRP, then
 the router MUST specify the HSRP virtual MAC address in any proxy ARP
 responses it generates.  These proxy ARP responses MUST not be
 suppressed based upon HSRP state.  Suppression based upon state could
 result in lack of any proxy ARP response being generated, since these
 proxy ARP responses may be suppressed due to other reasons, such as
 split-horizon rules.

7. Security Considerations

 This protocol does not provide security.  The authentication field
 found within the message is useful for preventing misconfiguration.
 The protocol is easily subverted by an active intruder on the LAN.
 This can result in a packet black hole and a denial-of-service
 attack.  It is difficult to subvert the protocol from outside the LAN
 as most routers will not forward packets addressed to the all-routers
 multicast address (224.0.0.2).

8. References

 [1] Deering, S., "ICMP Router Discovery Messages", RFC 1256,
 September 1991.
 [2] United States Patent.  Patent Number : 5,473,599.  Standby Router
 Protocol.  Date of Patent: Dec. 5, 1995.
 [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
 Levels", BCP 14, RFC 2119, March 1997.

Li, et. al. Informational [Page 15] RFC 2281 Cisco HSRP March 1998

9. Authors' Addresses

 Tony Li
 Juniper Networks, Inc.
 3260 Jay St.
 Santa Clara, CA 95054
 Phone: (408) 327-1900
 EMail: tli@juniper.net
 Bruce Cole
 Juniper Networks, Inc.
 3260 Jay St.
 Santa Clara, CA 95054
 Phone: (408) 327-1900
 EMail: cole@juniper.net
 Phil Morton
 Cisco Systems
 170 Tasman Dr.
 San Jose, CA 95143
 Phone: (408) 526-7632
 EMail: pmorton@cisco.com
 Dawn Li
 Cisco Systems
 170 Tasman Dr.
 San Jose, CA 95143
 Phone: (408) 527-2014
 EMail: dawnli@cisco.com

Li, et. al. Informational [Page 16] RFC 2281 Cisco HSRP March 1998

10. Full Copyright Statement

 Copyright (C) The Internet Society (1998).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
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