Hot Standby Routing Protocol otherwise known as HSRP is considered to be a Cisco proprietary protocol that would be allowing two or more routers so as to work together for representing a single IP address for a particular network. HSRP, as well as VRRP (Virtual Route Redundancy Protocol),  are considered high-availability network services that would be allowing for almost immediate failover to a secondary interface when the primary interface would become unavailable.

HSRP is considered to be a fairly simple concept that would have worked by having one router within an HSRP group which would be selected as the primary or active router. That primary would be handling all routing requests while the other routers within the HSRP group that would be simply waiting in a standby state. These standby routers would be remaining ready to take on the entire traffic load if the primary router would become unavailable. In this scenario, HSRP would be providing high network availability since it routes IP traffic without having to be dependent on a single router.

The hosts that would be using the HSRP address considering it as a gateway that would never know the actual physical IP or MAC address of the routers in the group. Only the virtual IP address which was created within the configuration of the HSRP along with a virtual MAC address which would be known to other hosts on the network.

Basic HSRP Configuration

For this scenario, you have to use a topology that would be consisting of just two routers. Keep in mind that one or both of these routers would be multilayer switches like a 6509 or 3750 as well. But just for this discussion let us just refer them as routers.

Controlling the Active HSRP Router

There are more HSRP values that you are going to need to change from time to time so as to ensure the complete control over your network traffic. As for example, what if we would be wishing R1 to be the Active router instead of R2?  To force a particular router so as to be the active router in an HSRP group you are going to need to use the priority command. The default priority is supposed to be about 100.  The higher priority would be determined which router is going to be active.  If both routers would be set up to the same priority, the first router to come up would be considered as the active router.

Keeping the Active Router Active

In the scenario which is mentioned above, if R1 fails, R2 would be becoming active.  This is perfect!  But, if R1 comes back up and returns to service, R2 would be continued to stay active.  This might not be a preferred behavior.  There are times when you might be always wanted R1 to be in an active state in the HSRP group.  Cisco would provide a way to getting used to controlling this by utilizing the Preempt command.  Preempt would be forcing a router in order to be active after recovering from a failure.

Advanced HSRP Configuration – Load Balancing

So now you would be able to see how great HSRP is and how it would be allowing us to have high availability between multiple routers for a single network.  But the standby routers wouldn’t be doing anything and are just sitting there!   It is going to be depending on the model router that you would be utilizing, this could be a lot of money just sitting idle.

In order to solve this problem, we could configure HSRP so as to be load balanced between routers.  This isn’t going to help us with a single HSRP group, but for multiple HSRP groups, we could just spread the load and have each HSRP group to remain active on different routers. By configuring several HSRP groups on a single interface, load balancing of HSRP could be achieved.

If you wish to learn more about configuring the HSRP on Router, all you need to do is to join the courses, offered by the SPOTO and learn it all through their expertise training modules.