Definition and purpose
HSRP (Hot Standby Router Protocol) is a Cisco first-hop redundancy protocol that helps maintain a default gateway when a router fails.
Technical operation
Routers share a virtual gateway address within an HSRP group. The active router normally forwards traffic while a standby router can take over. Priority, preemption and interface tracking affect the election and failover behavior.
Practical example
In a user VLAN, two layer-3 switches provide the same virtual default gateway. If the active device stops working, the standby takes over after a convergence interval.
Operational considerations
HSRP does not replace dynamic routing or WAN redundancy. Test upstream failures, configure suitable authentication and monitor state transitions rather than assuming failover is instantaneous.