What is HSRP, Why do we use it, and How to do HSRP config on Cisco Router?

HSRP is an FHRP (First Hop Redundancy Protocol) developed by Cisco to provide redundancy and high network availability almost anywhere in the network where we have two layer3 devices. HSRP config gives a group of routers a virtual IP address and a virtual MAC address to look like one router. If one router doesn’t work, the other router can be the default gateway. The virtual router does not exist; it is merely a target for routers to provide backup to one another. One router is designated as the active router, while the other is marked as the standby router, which takes over management of the group’s virtual MAC address and IP address if the active router fails.

HSRP protocol is also known as gateway load-balancing protocol. There are two other Gateway load balancing and redundancy protocols; namely VRRP and GLBP. The main idea behind HSRP is to create redundant default gateway addresses. It effectively creates active and standby routers. If there is a router failover, the HSRP protocol will ensure that all the network ip traffic will automatically switch routes, and the network will stay functional without any interruption.

You can also check another deep dive blog post about similarities and differences between VRRP, HSRP, and GLBP.

Watch this short video in order to get a quick understanding of HSRP. If you are viewing on a big screen like a laptop or PC, click on the square box on the right side of the video to enlarge it on the screen. You do not need to do anything if you are watching on mobile.

HSRP Config Guidelines and Steps

Points to be noted while doing HSRP Configuration Cisco

• It is a good practice to change HSRP from default version 1 to version 2. Version 2 is the latest and is not backward compatible with version 1.
• Preemption should be enabled on both routers.
• A layer 3 interface can be a layer 3 interface on a router or a switch. It can be a routed port or an SVI, or simply a layer 3 EtherChannel interface.
• Do not forget to assign a layer3 IP address on the layer3 interface.
• When you change the HSRP version, the interface resets and assigns a new virtual mac address.

You can further check to configure HSRP cisco product-specific guidelines for more details.

HSRP Versions

It has two versions.

HSRP v1 – It is the default version on cisco devices. You can configure HSRP group numbers from 0 to 255, and it uses multicast address 224.0.0.2 to send hello packets.

HSRP v2 – This is the latest version. Here HSRP group numbers can be from 0 to 4095, and it uses multicast address 224.0.0.102 to send hello packets.

First step in setting up HSRP

Let’s start by configuring our HSRP cisco setup. For this demonstration, I have used a simplified GNS3 network setup shown below.

Startup Configuration

Now let’s configure R1 and R2. I am using the standby group number as 1 and the virtual IP 192.168.100.1 on both routers inside the sub-interface configuration command.

If logs are enabled on the Cisco router, you will see different state change notifications. This will confirm that our devices are configured properly.

Router-1 changes its state from Speak to Standby to Listen and then finally elects to be “standby.”

Router-2 changes its state as well from Speak to Standby and then Standby to Active. And then finally announces itself to be “Active.” Normally, when you do not configure any priority, the configured interface with the highest IP address becomes Active.

A ping from PC-1 at this point should be successful.

Let us check ARP details on Routers.

Check ARP on R1.

Let’s use the show standby command on R1 and R2 to check details.

The default version of HSRP is v1.

HSRP default priority is 100.

Virtual mac is 0000.0c07.ac01

Preemption is disabled by default.

Now let’s check on R1.

Let us change some of the things based on the design recommendation from cisco.

Quick Tip:- You can check the changed version and preemption by the “show standby” Command.

How to configure HSRP Priority

Next, change the default priority(100) on router R1 and make it an active router.

You will see the below message on the console, changing the state from standby to active state. Now, R1 is Active since it has the highest priority among R1 (now 110) and R2 (100).

Let’s check this with another useful command, “Show standby Brief.”

Now R1 router is local. Let’s confirm this on R2 as well.

Since we have changed the active router to R1 now, let us check from PC1 whether we can ping the Virtual gateway or not.

And it is working., which is all hunky-dory.

Testing of the Setup

It is always advisable to test our setup.

Let’s shut down the R1 Fa0/0 router interface while continuously pinging 192.168.100.1 from PC1.

There were no drops from PC1, but you may see 1 or 2 drops in an actual production network.

You will see the below messages on the console on R1.

Let’s enable R1 fa0/0 and check whether “preemption” is working properly or not.

You will following message on the console, which confirms that R1 is Active now for Fa0/0.100

HSRP Tracking feature

We will be extending our network setup and will use R3 as a WAN connection to showcase the tracking feature.

Let us test a scenario when our Primary WAN link connected to R3 from R1 fails. 

We definitely want our Active router to change from R1 to R2 automatically in this case.  

We will use the Object tracking feature, which basically monitors an interface/IP and reduces the priority of the Active router (R1) to make it less preferable than the secondary router (R2).

Let us configure and test it.

The first step is to configure our track to monitor the Fa0/1 line protocol in global configuration mode.

And then, the next step is to attach the track to HSRP group 1 under the Fa0/0.100 sub-interface configuration mode.

Let us check the status on R1.

R1 is Active for HSRP group 1 on R1.

Now let’s test it by shutting down Interface fa0/1 on R1.

You will see the following message on the R1 console.

Let’s Check the status on R1. You can see that now R1 is acting as standby.

Let’s test this setup from a workstation (VPCS-1) point of view as well.

Now trace to R3’s loopback interface is landing up to R2 in this case, which is perfect as R2 is Active for group 1 now.

P.S – Don’t worry about the ICMP failures, because there is no reverse route from R3 to VPCS-1 ip address, the reverse traffic will fail.

How to configure Advanced Multiple HSRP config for load balancing

In Hot Standby Router Protocol, load balancing is achieved by using multiple HSRP groups. Routers configured for HSRP can belong to multiple groups and multiple VLANs. By configuring one group to be active for R1 and standby for R2, and the second group to be active for R2 and standby for R1, both routers R1 and R2 can be used to pass ip traffic, as opposed to one sitting idle.

R1 serves all Vlan 100 clients in this normal operation while R2 monitors and waits for R1 to failover. This is not a very good use of resources. Now let’s spice up our HSRP config by doing load-balancing across due routers within the same VLAN 100.

First, change the PC2 gateway to 192.168.100.100, which we will configure in our next step.

Now let us configure a new HSRP group 2 on R1 and R2 within the same sub-interface (fa0/0.100) to support our Multiple HSRP design. This time, we will make R2 an Active router for group 2.

You will see notifications on the console, and now R2 is an Active router.

Let’s ping 192.168.100.100 from PC2 and confirm.

Wow, our setup is working.

Let’s recap what we have done so far.

• PC1 and PC2 in VLAN 100.
• PC1 is pointing towards R1 and PC2 towards R2.
• I have added R3 in this setup to prove that this setup is working as expected.
• PC1 is going through R1, which has Fa0/0.100 ip configured as 192.168.100.2

• PC2 is going through R2, which has Fa0/0.100 ip configured as 192.168.100.3

Don’t worry about the (Destination Host unreachable) message; it has appeared because there is no reverse route configured from R3.

How to make HSRP more secure with Authentication

You can also secure the HSRP protocol by configuring Authentication. I will not go deep into this topic as it is comparatively easy, and once you understand the basic functionality and use case of HSRP, you will get the hang of it.

HSRP includes an authentication mechanism. You can opt for either plaintext or MD5. Follow these steps to configure MD5: 

R1 & R2

This guarantees authentication of all packets that are sent between the two routers. This prohibits anyone from joining our HSRP configuration on the 192.168.100.0/24 subnet.

How to make HSRP more responsive with Timers

By default, HSRP is somewhat a slow protocol, as it has 10 seconds of hold-time time before the standby router takes over the active role. Therefore, you should always tweak it to match your company’s SLA. 

Let us configure hello time to 50 milliseconds and the hold time to 150 milliseconds. 

You can check by this show standby command.

Common Troubleshooting steps with HSRP

Sometimes things do not work been even if you have taken all necessary steps to configure HSRP properly. For those times , be mindful of these steps when facing any HSRP related issue –

• Check if HSRP routers are on the same network segment.
• Check HSRP virtual ip is configured as gateway ip on hosts.
• Check HSRP configuration on both routers for any mismatch on VLANs, ip subnets, standby groups, virtual ips etc.
• Check if VLANs are allowed between two Devices where HSRP is configured. Especially when there is a layer2 switch in between.
  Check if the interface is enabled.

Useful commands for HSRP Config Cisco

show standby –> The command show standby can be used to display detailed information about HSRP groups of which a switch is a member. This command would not provide a quick view. This command displays information about HSRP on all configured interfaces and for all HSRP groups. It also displays hello timer information and the expiration timer for the standby switch.

show standby brief –> The command show standby brief should be used to quickly view the HSRP state of a cisco router or a switch for all HSRP groups of which it is a member. The summary information it provides includes the group number, priority, state, active device address, standby address, and group address.

show ip interface brief –> The command show ip interface brief is useful in that lists the interfaces and displays the basic IP configuration of each. This output would include the IP address of the interface and the state of the interface, but not HSRP information.

Debug standby –> Shows all HSRP related errors, events, packets, and state transitions.

show run –> Displays the entire configuration of the cisco device.

Definitions and Acronyms used in the post

HSRP – Hot Standby Router Protocols

FHRP – First Hop Redundancy Protocol

Quiz

Conclusion

In this post, we have looked into HSRP protocol configuration, which provides gateway level redundancy for uninterrupted network connectivity when any single gateway fails. Furthermore, we have enhanced our configuration by providing load balancing traffic among two routers by Multiple HSRP.

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