Cisco Hot Standby Router Protocol (HSRP)
RFC 2281

Document Type RFC - Informational (March 1998; Errata)
Was draft-li-hsrp (individual)
Last updated 2013-03-02
Stream Legacy
Formats plain text pdf html bibtex
Stream Legacy state (None)
Consensus Boilerplate Unknown
RFC Editor Note (None)
IESG IESG state RFC 2281 (Informational)
Telechat date
Responsible AD (None)
Send notices to (None)
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
Show full document text