RFC 2281 (rfc2281) - Page 2 of 17
Cisco Hot Standby Router Protocol (HSRP)
Alternative Format: Original Text Document
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