VRRP

What is VRRP?

VRRP (Virtual Router Redundancy Protocol) is a widely adopted standard designed to establish a virtual gateway, similar in function to HSRP (Hot Standby Routing Protocol). It allows LAN hosts to use local, redundant routing devices through a single static default route configuration. This approach simplifies host routing while ensuring high availability. Commonly implemented on Ethernet networks (including fast, gigabit, and 10-gigabit), as well as logical interfaces, VRRP is typically configured in an active/passive, or primary/backup, setup, ensuring seamless failover in case the primary router becomes unavailable.

How Does VRRP Work?

VRRP Device Priority and Failover Handling

VRRP provides simplicity and high availability, allowing a group to support up to 255 devices. The VRRP mechanism dynamically assigns priority to compatible devices, but administrators can manually set priority levels ranging from 1 (lowest) to 255 (highest) for each VRRP device.

This setup has significant implications. First, the system will select a new primary router based on priority if the current primary fails. If a new VRRP router with a higher priority joins the network, it may take over as the primary. However, this behavior is not guaranteed; the system might also choose to maintain the original primary as the backup, even in the presence of a higher-priority router.

VRRP Functional Overview

Here’s a concise overview of how VRRP operates:

• A virtual IP address is assigned from the local subnet, serving as the default gateway for local hosts.

• The last eight bytes of the VRRP hexadecimal group number are used to generate a virtual MAC address. By default, VRRP employs the MAC address format 0000.5e00.01xx, replacing the last two digits with the group hex number.

• The member with the highest priority in the VRRP group becomes the primary device and starts forwarding traffic. If two members share the same priority, the device with the higher IP address is chosen.

• All other VRRP devices serve as backups.

• The primary router sends multicast keep-alive messages to backups every second.

• If a backup doesn’t receive the master advertisement within a set timeframe, it assumes the primary role. This is the preempt function.

• The VRRP group continuously monitors for status changes, facilitating dynamic priority assignments and master router selection.

• VRRP supports plain-text authentication, MD5 authentication, or no authentication at all.

Why is VRRP Beneficial?

VRRP focuses on redundancy and intelligent traffic routing, eliminating the need for manual configuration of backup devices while allowing for detailed administration. This approach prevents network performance from being tied to a single point of failure. In typical deployments, VRRP for IPv6 provides a much faster switchover to an alternate default router than IPv6 neighbor discovery procedures, often utilizing only one backup router.

As VRRP manages traffic routing, it is commonly used in load balancing environments. Its ability to simplify host configuration further enhances overall network performance.