First Hop Redundancy Protocol (FHRP)

1) A First Hop Redundancy Protocol (FHRP) is a computer networking protocol that is designed to protect the default gateway used on a subnetwork by allowing two or more routers to provide gateway redundancy, in the event of failure of an active router, the backup router will become active, usually within a few seconds.

2) The primary purpose of FHRPs is to designate a backup router that can take over the responsibilities of the primary router if it fails, thereby minimizing downtime and ensuring continuous network connectivity.

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Popular First Hop Redundancy Protocols

 

1) Hot Standby Router Protocol (HSRP): Developed by Cisco, HSRP is one of the earliest FHRPs. It allows for the creation of a virtual IP address and a virtual MAC address that float between the primary and backup routers. HSRP operates at the data link layer (Layer 2) and is widely used in Cisco environments.

2) Virtual Router Redundancy Protocol (VRRP): Similar to HSRP, VRRP is an industry-standard FHRP. It provides redundancy by allowing a group of routers to work together as a virtual router. VRRP operates at the network layer (Layer 3) and is not vendor-specific, making it interoperable across different networking devices.

3) Gateway Load Balancing Protocol (GLBP): Another Cisco protocol, GLBP combines the features of load balancing and redundancy. It dynamically assigns different virtual MAC addresses to different routers in the GLBP group, distributing the traffic load efficiently.

 

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HSRP Features

1. Exchange a Hello message every 3 seconds.
2. Multicast IP for HSRP version 1 = 224.0.0.2
3. Multicast IP for HSRP version 2 = 224.0.0.102
4. UDP port number = 1985
5. Arbitrary group number = 0 -255
6. The default priority is 100, range is 0-255

HSRP Interface States

1) Disabled / Initial = This is the state at the start. The State indicates that HSRP is not running.

2) Learn = The router has not determined the virtual IP address and has not seen a Hello Message from the active router.

3) In this state router waits to here the Hello message from the active router.

4) Listen = The Router knows the virtual IP Address but the router is neither an active router not a standby router.

5) Speak = The router is a candidate to become the next active router and sends periodic Hello messages.

6) Active = The router currently forwards packets that are sent to the group virtual MAC Address.

Configuration

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Initial Setup

First, we will configure the HSRP standby group, assign the VIP along with assign a higher priority on R1.

Configure HSRP with group number 1 on R1 and R2 such that R1 will act as an Active Router and R2 will act as a Standby Router.

Router1:

R1 (config) # interface fastEthernet 0/1

R1 (config-if) # standby 1 ip 192.168.0.254

Note: Above command will configure HSRP with group number 1 and Virtual IP address 192.168.0.254

 

R1 (config-if) # standby 1 priority 100

Note: Above command will configure R1 as Active Router.

 

R1 (config-if) # standby 1 preempt

R1 (config-if) #exit

Router2

R2 (config) #interface fastEthernet 0/0

R2 (config-if) # standby 1 ip 192.168.0.254

R2 (config-if) # standby 1 preempt

R1 (config-if) #exit

Verification

To check the HSRP config on R1 and R2

 

To verify we look for the preemption flag and also that the state is showing as active.

 

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Conclusion

First Hop Redundancy Protocols are indispensable components of a robust network infrastructure. 

By implementing FHRPs like HSRP, VRRP, or GLBP, organizations can enhance network reliability, minimize downtime, and ensure uninterrupted communication. 

As technology continues to evolve, understanding and adopting FHRPs become increasingly critical for maintaining a resilient and high-performance network environment.

Author:-

Gandhar Bodas

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