Hot Standby Router Protocol

The Hot Standby Router Protocol (HSRP) makes sure that when access circuits or network edge devices have first-hop failures, user traffic is instantly and transparently restored. With HSRP, you can set up two or more routers as standby routers and just one router as active at once. The Hot Standby Router Protocol (HSRP) allows devices in the HSRP group to send and receive data. There are two variants of the protocol, version 1 and version 2.

Hot Standby Router Protocol (HSRP)

A local subnet (To know more about subnets, check out this article) has redundancy thanks to the CISCO proprietary Hot Standby Router Protocol (HSRP). In HSRP, the illusion of a virtual router is created by two or more routers. With HSRP, you can set up two or more routers as standby routers and just one router as active at once. It makes sure that when access circuits or network edge devices have first-hop failures, user traffic is instantly and transparently restored.

Working of HSRP

1. Members of the same group are those who share the same group ID. One group member will be chosen to serve as the active router, with the rest acting as backup routers.
2. All hosts in the local subnet have the virtual IP set as their default gateway, and the active router is in charge of routing local host traffic. The standby router waits until the hold-down timer time if the active router goes down.
3. The standby router will switch over to become the active router as soon as the hold-down period is through and assume all of the duties of the active router.

HSRP Router Roles

HSRP Groups enable the Hot Standby Router Protocol. There are various routers, each with a distinct role, for each group. There are three roles:

Active Router

The router through which traffic flows is known as the Active Router. Active traffic flow is provided by the router.

Standby Router

The Standby Router serves as the Active Router’s backup. This router becomes active and directs traffic through it when the main router fails.

Listening Routers

The additional routers taking part in the HSRP group are known as Listening Routers.

HSRP States

Active: The device is actively forwarding traffic.

Init: A device in this condition is not yet prepared or capable of taking part in HSRP.

Learn: When neither the virtual IP address nor a hello message from an active device has been established, the device is in this state.

Listen: Whenever a device is receiving hello messages, it is in this state.

Speak: Whenever a device is sending and receiving hello messages, it is in this state.

Standby: A device in this condition is ready to take over traffic forwarding responsibilities from an active device.

HSRP Versions

There are two variants of the Hot Standby Router Protocol (HSRP):

• Version 1: The messages use UDP port 1985 and are multicast to 224.0.0.2. The group number range in this version is 0 to 255.
• Version 2: The messages use UDP port 1985 and are multicast to 224.0.0.102. The range of group numbers allowed in this version is 0 to 4095.
  

Conclusion

Let’s conclude what we learned in this article:

1. With Hot Standby Router Protocol or HSRP, you can set up two or more routers as standby routers and just one router as active at once.
2. One group member will be chosen to serve as the active router, with the rest acting as backup routers.
3. The Standby Router serves as the Active Router’s backup.
4. All hosts in the local subnet have the virtual IP set as their default gateway and the active router is in charge of routing local host traffic.
5. There are two versions of the protocol, version 1 and version 2.