RFC 2281 (rfc2281) - Page 2 of 17

Cisco Hot Standby Router Protocol (HSRP)

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