Hot Standby Router Protocol
HSRP or Hot Standby Router Protocol is a protocol defined by Cisco and now described in rfc2281.
Contents
Purpose of HSRP
The purpose of HSRP is to ensure network connectivity in case of Router or access circuit failure, by having one or more standby Router(s) waiting to take over from the failing active Router.
Other high availability Router protocols
How does HSRP work
HSRP works by two or more Routers agreeing upon which Router serves the virtual Router.
The Virtual Router
The Virtual Router is a MAC-address and a IP Address the active Router serves beside its configured IP address. If the active Router fails one of the standby Routers becomes the Virtual Router by serving the virtual MAC-address and IP Address.
HSRP exampleIn picture 1 three Routers R1,R2 and R3 are setup in a HSRP Group. The Virtual IP address 10.0.0.1 and virtual MAC-Address 00-10-0C-07-AC-0A are served by the active Router R1. R1 continuesly transmits hello packets to the standby Routers. |