What is HSRP in Networking?

Introduction

Redundancy is a crucial component of every modern network. In this digital era, staying without a network for even a short time is hard. You should include some redundancy if you don’t want your firm to cease operating. All of your devices will stop communicating with the outside world if the default gateway fails since they all point to it. That’s where HSRP comes into action, but what is HSRP in networking? The Hot Standby Router Protocol (HSRP) enables a backup router to take control of the default gateway.

In this blog, we will discuss HSRP in networking in detail, it’s working, why we need it, its benefits, and drawbacks. Let’s Begin!

What is HSRP in Networking?

HSRP in Networking or Hot Standby Router Protocol is a Cisco proprietary redundancy protocol for default gateway configuration in a network and fault tolerance. In order to maintain network connection even when one of the routers fails, HSRP enables several routers to cooperate and provide a single virtual router to the linked hosts.

In an HSRP, routers in a group speak to one another via User Datagram Protocol (UDP) port 1985 using the multicast address 224.0.0.2. One router is chosen to serve as the group’s “active” router, which is in charge of forwarding traffic, and another is chosen to serve as the group’s “standby” or “backup” router, which assumes control in the event that the active router fails.

History of HSRP

HSRP stands for Hot Standby Router Protocol, a Cisco proprietary protocol that provides redundancy and load balancing for network routers. HSRP was first introduced in 1998, described in RFC 2281, and has been updated several times since then. The main updates are:

• HSRP version 2, released in 2001, which supports IPv6 and longer group names.
• HSRP for IPv6, released in 2006, allows HSRP to run over IPv6 networks without requiring IPv4 compatibility.

As per the requirements, new patch update or enhancements has been made for better functioning.

Before getting into the workings of Hot Standby Router Protocol, let’s first understand why HSRP is required.

The Need for Hot Standby Router Protocol

A device either has a static IP address or asks a DHCP server for a dynamic one. The device will always have an IP address, a subnet address, and the address of its default gateway. Unfortunately, the default gateway IP address can only be stored on a small number of devices. As a side effect, they will just point to a black hole if that gateway malfunctions. Outside of their subnet, they won’t be able to communicate with one another.

You will experience significant downtime if the default gateway fails. As a result of this, the router faces a Single Point of Failure (SPoF). As you can see in the image below, if the router fails, then the network will be isolated.

Also, if we take the case of the switch, the device that is connected to it will not be able to access the internet. But a switch is not SPoF; it will not impact the whole infrastructure of the company. Learn the difference between Switch and Router.

Now, the question that arises is how to overcome this issue.

For this type of scenario where SPoF occurs, we do this by setting up HSRP on the two routers. Instead of informing the customers, we set up the backup gateway to pass as the main one in the event of a primary gateway failure.

You must add a Virtual IP Address (VIP) to both routers in order to complete that setup. It will only be used by the main router by default. However, the backup router will begin utilizing that IP if the main one fails. For better understanding, we have taken an example.

Let’s now understand the different states of Hot Standby Router Protocol.

Hot Standby Router Protocol States

The various HSRP states are listed below:

Active

The router sends periodic hello messages and forwards packets for the HSRP group.

Init

The router doesn’t send or receive HSRP messages and is not an HSRP participant.

Learn

The router is learning the HSRP group’s virtual MAC address and IP address.

Listen

The router monitors both the active and standby routers’ HSRP hello messages.

Speak

The router is participating in the election of the active and standby routers and transmitting HSRP hello messages.

Standby

The router periodically sends hello signals and waits to take over as the active router.

How does HSRP work?

Below, we have explained the working of HSRP in detail.

Configuration

HSRP is set up on routers connected to the same local area network (LAN) by network administrators. They allocate routers to an HSRP group with a certain group number.

Additionally, a priority value is given to each router in the group (the default is 100), which establishes that router’s place in the group.

Election process

When routers have HSRP enabled, they communicate using HSRP hello messages to find one another and choose which routers are active and standby depending on priority settings. The router with the greatest priority is made active, and the router with the next-highest priority is made available as a standby. The router with the higher IP address prevails in cases when both have the same priority value.

MAC address and virtual IP address

A virtual IP address and virtual MAC address are shared by all group members in a HSRP group. The end devices’ default gateway address is typically specified as the virtual IP address. The virtual MAC address has the following format: 0000.0C07.ACxx, where xx is the hexadecimal representation of the HSRP group number.

Active router role

The virtual IP address’s active router relays traffic on its behalf. In order to keep its position and update the other routers in the group on its status, it also regularly broadcasts HSRP hello messages (the default interval is 3 seconds).

Standby router role

When the active router sends an HSRP hello message, the standby router waits for it. If it doesn’t get any hello messages from the current router for a certain amount of time (the default is 10 seconds), it is ready to take over as the active router.

Failover process

The standby router takes over as the active router if the current router fails or becomes inaccessible. Starting the traffic forwarding process, it adopts the virtual IP and MAC addresses. A new standby router is chosen in the meantime from among the group’s remaining routers using priority values.

Recovery

Depending on its priority value and preemption settings, the failed active router either rejoins the HSRP group as a standby router or assumes its previous active function.

High availability and redundancy are provided by HSRP, which ensures network traffic keeps moving even if a router malfunctions.

HSRP Configuration

In this lab you’ll configure and test HSRP (Hot Standby Router Protocol) for a small campus network to ensure the
recovery of user traffic transparently and immediately from first hop router failures.

Create a topology like shown below:

Configure the IP addresses on R1, R2 and R3. Then configure the virtual IP address 192.168.10.254 /24 using the
commands given below.

R1:
R1(config)#int fa 0/0
R1(config-if)#standby ip 192.168.10.254
R1(config-if)#ex

Now, configure the same IP address on R2’s interface.
R2(config)#int fa 0/0
R2(config-if)#standby ip 192.168.10.254
R2(config-if)#ex

Let’s check which router out of R1 and R2 is in active state. Use the command ‘show standby’ in the enable mode to
check the details.

In this topology, R1 is in active state.

Configure DHCP pool on R1 and R2 with the default gateway as 192.168.10.254 and R3 with 192.168.30.3

R1:
R1(config)#ip dhcp pool a
R1(dhcp-config)#network 192.168.10.0 255.255.255.0
R1(dhcp-config)#default-router 192.168.10.254
R1(dhcp-config)#ex

R2:
R2(config)#ip dhcp pool a
R2(dhcp-config)#network 192.168.10.0 255.255.255.0
R2(dhcp-config)#default-router 192.168.10.254
R2(dhcp-config)#ex

R3:
R3(config)#ip dhcp pool a
R3(dhcp-config)#network 192.168.30.0 255.255.255.0
R3(dhcp-config)#default-router 192.168.30.3
R3(dhcp-config)#ex

Now, the last step is to configure routing on the devices. We are configuring EIGRP 1 here.

R1:
R1(config)#router eigrp 1
R1(config-router)#no auto-summary
R1(config-router)#network 192.168.10.0
R1(config-router)#network 192.168.20.0
R1(config-router)#ex

R2:
R2(config)#router eigrp 1
R2(config-router)#no auto-summary
R2(config-router)#network 192.168.10.0
R2(config-router)#network 192.168.20.0
R2(config-router)#ex

R3:
R3(config)#router eigrp 1
R3(config-router)#no auto-summary
R3(config-router)#network 192.168.20.0
R3(config-router)#network 192.168.30.0
R3(config-router)#ex

After configuring the end devices with the IP address let’s test the working of HSRP.

Run a continuous ping from PC0 to PC1 using command ‘ping -t 192.168.30.1’ and shutdown the interface fa 0/0 of R1.

R1(config)#interface fa 0/0
R1(config-if)#shutdown

You’ll observe that PC0’s will recover from the R1’s route failure and will start transmitting through R2.

Reply from 192.168.30.1: bytes=32 time<1ms TTL=126
Reply from 192.168.30.1: bytes=32 time<1ms TTL=126
Request timed out.
Request timed out.
Reply from 192.168.30.1: bytes=32 time<1ms TTL=126
Reply from 192.168.30.1: bytes=32 time<1ms TTL=126

Now, if you check the HSRP details on R2 using command ‘show standby’ you’ll find it in the active state.

We have a detailed understanding of how HSRP functions, so let’s discuss the advantages and disadvantages of using HSRP.

Advantages of Hot Standby Router Protocol

Here are the main advantages –

• Redundancy – Using an active and a standby router inside an HSRP group, HSRP enables the establishment of redundant gateway configurations. The standby router takes over in the event of an active router failure, providing no downtime for the network.
• High Availability – A router is always available to forward traffic for the connected hosts, thanks to HSRP. By doing this, network uptime is increased, and end users’ connection is maintained.
• Seamless Failover – In the event of a breakdown, HSRP offers a smooth switch from the active router to the backup router. This maintains a steady network environment by reducing packet loss and interruption to the linked hosts.

Disadvantages of Hot Standby Router Protocol

Although HSRP provides advantages, there are a number of disadvantages to take into account:

• Proprietary protocol – Since HSRP is a Cisco-specific protocol, only Cisco-branded hardware may use it. In a network setting with several vendors, this may restrict interoperability.
• Scalability – Large or sophisticated networks are not intended for HSRP. It is appropriate for small and medium-sized networks, but bigger settings with many routers and subnets could not scale effectively.
• Active/standby model – One router serves as the active router in HSRP, while another serves as the backup router. The backup router is inactive until a failure occurs, which implies that only one router actively sends traffic. This might lead to the underutilization of the backup router and the wasteful use of resources.

Now, we have understood everything related to HSRP in networking. Let’s wrap this article.

Frequently Asked Questions

Q1 – Why HSRP is used in networking?

HSRP is a Cisco proprietary protocol that enables two or more routers to work together to offer a network with redundancy and load balancing.

Q2 – What is HSRP and VRRP?

HSRP, or Hot Standby Router Protocol, is a Cisco proprietary, which means it is suitable for Cisco devices, whereas VRRP, or Virtual Router Redundancy Protocol, is an open standard protocol that is suitable for a variety of vendors.

Q3 – Is HSRP a layer 2 or 3 network?

HSRP is a layer 3, i.e., network layer protocol.

Q4 – Is HSRP and VRRP the same?

HSRP and VRRP are both protocols that provide redundancy for routers in a network. HSRP is specially developed for Cisco devices, whereas VRRP supports various vendors.

Conclusion

In this blog, we have explained what is HSRP in networking, how it works, different HSRP states, the need for Hot Standby Router Protocol, advantages and disadvantages. If you want to learn HSRP in detail, you can join PyNet Labs’ CCNA Course.

If you have any suggestions or queries, feel free to comment below.