HSRP (Hot Standby Router Protocol)

Hot Standby Router Protocol (HSRP)

HSRP(Hot Standby Router Protocol) is a Cisco proprietary First Hop Redundancy Protocol (FHRP). HSRP first hop redundancy mechanism provides alternative path as a proactive action for any failure on a device. In this lesson, we will learn the protocol and in the following lessons, we will also learn HSRP Configuration. You can also view related RFC here.

With Hot Standby Router Protocol mechanism, even if a failure occurs on one device in the HSRP Group, then the traffic goes through on another device in that Group, through an alternative path.

Hot Standby Router Protocol provides this by using a Virtual IP address and a MAC address as a Gateway of multiple path alternatives. The traffic is always go to the Virtual IP address, Virtual Gateway. So, the traffic flow is independant from a device. This avoids single point of failure on the networks.

By the way, HSRP Group numbers is mention at the beginning of the confiugration after “standby” keyword. There can be multiple groups of HSRP on an interface.

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HSRP Router Roles

Hot Standby Router Protocol works with HSRP Groups. For each group, there are different routers that has different roles. These roles are:

• Active Router
• Standby Router
• Listenning Routers

The Active Router is the router that the traffic flow go through this router. It is the router that actively take place in the traffic flow in normal case.

The Standby Router is the backup of Active Router. When th active router fails then this router become Active and the traffic go through this router.

Lastly the Listening Router is other routers that are participating in the HSRP group.

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Active/Standby Elections

The main two roles of HSRP are Active and Standby. For these roles, routers does an election between them. In this election two parameters are important. The elections are done according to two parameters. These are:

• Priority Values
• Interface IP Addresses