Hot Standby Router Protocol (HSRP) Overview: You’ve Got A Friend

When you’re down and troubled and you need a helping hand
And nothing, whoa, nothing is going right
Close your eyes and think of me and soon I will be there
To brighten up even your darkest nights

You just call out my name, and you know wherever I am
I’ll come running, oh yeah baby, to see you again
Winter, spring, summer, or fall
All you got to do is call and I’ll be there, yeah, yeah, yeah
You’ve got a friend

Whenever I see Hot Standby Router Protocol (HSRP), it always reminds me of a song. As what James Taylor said, “You’ve Got a Friend.” If you already know what HSRP is, you might’ve as well other things that make you remember what it does.

If you’re kinda new and trying to understand what this is, this is a good start as I will not make this topic complicated. Although there are lots of things to tackle with HSRP, we will stick with the basics and some links are provided below to further discuss other HSRP topics.

HSRP is not a router and definitely not a routing protocol. When I first studied HSRP, the first thing that came up in my mind is that this is a routing protocol like EIGRP, BGP, OSPF, or RIP but it isn’t as it does not affect the routing table.

HSRP is a Cisco proprietary redundancy protocol. One device will act as active and the other is passive. Once the active device is down, the passive device will take over. The active device will be responsible for handling the traffic of the VIP (virtual IP). Since the VIP is shared between these two devices, when the active device fails, traffic will failover to the standby device. However, keep in mind that pre-emption is not enabled by default.

HSRP ELECTION: HSRP PRIORITY

What is the criterion for becoming the active device? -> the configured priority. The higher the priority value, the better. You can configure the priority value from 0-255. What if you don’t configure the priority value? Then the default is 100. What if they have the same priority value? Then, the highest configured IP address will be the active device.

NICE TO KNOW:

• You can configure up to 255 HSRP groups. It is locally significant so you can use the same HSRP group number for all the VLAN interfaces. However, it is recommended to match the group number with the VLAN number to avoid confusion or configuration error.
• HSRP uses a virtual MAC address of 0000.0C07.ACxx where xx is the hex value of the HSRP group number. For example,

a. HSRP group number is 1, then the MAC address is 0000.0C07.AC01
b. HSRP group number is 100, then the MAC address is 0000.0C07.AC64

HSRP TOPICS:

• HSRP Versions
• HSRP and Object Tracking
• HSRP Lab Configuration
• HSRP States
• HSRP Authentication
• HSRP Troubleshooting
• VPC and HSRP