HSRP - Hot standby Routing Protocol.

•        Cisco proprietary protocol only works on cisco routers and switches.

•        One active router and one standby router possible in a group.

•        Active router will be chosen based on priority ( default priority – 100, tie in priority, highest Ip wins).

•        Preemption allows a higher priority router to take over if it fails and come back online after some time.

•        Pre-emption disabled by default.

•        Upto 255 groups possible for load-balancing method.

•        Virtual mac 0000.0c07.ACxx. where xx is the hex-decimal no. of HSRP group.

•        Multicast IP for hellos – 224.0.0.2 in version 1 and 224.0.0.102 in version-2.

•        HSRP version 1 supports up to 255 groups and IPV4.

•        HSRP version 2 support up to 4095 and Ipv4 and ipv6 both supported.

•        Device tracking can be enabled to track the interface or route and perform a failover.

Note :- Preempt option only application for active role over taking, standby role doesn't need a preempt option.

HSRP lab test.

Configure Lab topology as per given routers.

Test a lab 1 with basic without preemption.

• Shutdown Active router and observe standby router takes place of active router.
• When active router comes back again it cannot be a active as preempt is disabled.

Test lab 2 with preemption

• Enable preempt only all both routers.
• shutdown active router and observe the behaviour.
• bring back the active router and observe the Behavious.

Note :- As preempt enabled and if we have higher priority on active router it will become Active again or else it will be on standby as already we have another active router in network.

If priority of both routers are different then higher priority router would become active always.

Test Lab 3 without Preemption and 3 routers.

Configure all routers with given topology.

R-1 HSRP priority - 150

R-2 HSRP priority - 120

R-3 HSRP priority - 200 ( dont add this router initially, we need to add this later).

• Bring the R1 and R2 up and observe R1 should become Active and R2 standby as per priority.
• now bring the R3 up and observer R3 takes the role of standby even with preempt disabled.
• shutdown R1 eth0/1 and observer R3 become active and R2 become standby.

This behaviour of R3 takes a standby role is becuase preempt only applies to active role takeover, for standby no preempt configuration required.

points to remember for HSRP with real time network

• Need to be carefull when adding new router in HSRP if not properly configured for lan and wan side and priority then it may bring the network down.
• only one active and one standby router possible and remaining all would be in a listen mode.
• Make sure to configure WAN/Destination tracking for failover.