Virtual Router Redundancy Protocol

This guide explains the functionality of VRRP and shows how to use it in a simple network environment and also in an enterprise network environment.

Introduction

VRRP is a protocol that allows for the creation of a virtual router on a network, made up of two or more physical routers working together. The virtual router acts as a single entity, with one of the physical routers designated as the active router and the other(s) serving as standby routers. The active router is responsible for forwarding packets, while the standby routers monitor the active router and take over if it fails. To implement VRRP, the physical routers are configured with a virtual IP address and a virtual MAC address, which are used by the virtual router. The active router sends periodic VRRP advertisements to the other routers on the network, announcing its status as the active router. The standby routers listen for these advertisements and take over as the active router if they stop receiving them. One of the benefits of VRRP is that it allows for the creation of a redundant network, with the virtual router taking over in the event of a failure of one of the physical routers. This helps to ensure high availability and prevent downtime. VRRP is often used in enterprise networks and other mission-critical environments where it is important to maintain continuous network connectivity.

General information in short
VRRP is a open standard, many different systems support this protocol
The active router is responsible for forwarding traffic for the virtual router, while the backup routers monitor the active router to ensure that it is still functioning
A virtual gateway address must be configured, and it is possible to use an IP address that is already used on an interface
Failover is the process of automatically switching to a backup or redundant system when the primary system fails
A router with a higher configured priority automatically becomes the active router after a failover - preemption is activated by default
Preemption is enabled by default
VRRP uses the MAC address 00:00:5e:00:01:?? (the last two depend on the configured VRRP group)
Avertisements are communicated via mulicast address 224.0.0.18
Default master advertisements timer = 1 second
Default master down interval = 3 * (Master advertisement interval) + [(256 - VRRP priority) / 256]
The priority range is 0 through 255, with 255 being the highest
The default priority is 100
VRRP uses the IP 112 network port
The Protocol is documented as RFC 3768

VRRP Version 3

The latest version is VRRPv3, which is defined in RFC 5798. VRRPv3 was designed to address some of the limitations of previous versions of VRRP and to improve the overall functionality of the protocol. Some of the key features of VRRPv3 include:

Description
Support for IPv4 and IPv6: VRRPv3 supports both IPv4 and IPv6, allowing it to be used in networks using either version of the Internet Protocol
Enhanced functionality: VRRPv3 includes additional features and functionality, such as the ability to load balance traffic across multiple routers and support for multiple virtual routers on the same physical interface
Backward compatibility: VRRPv3 is backward compatible with previous versions of VRRP, allowing it to be used in networks that may include older VRRP implementations

VRRP States

In a VRRP configuration with multiple routers, one of the routers is designated as the active router (also known as the master router) and the others are configured as backup routers. The active router is responsible for forwarding traffic for the virtual router, while the backup routers monitor the active router and take over if it fails. If the active router becomes unavailable, one of the backup routers is selected to take over as the active router. The selection process is based on the VRRP priority configuration of the routers. The router with the highest priority becomes the active router, and if multiple routers have the same priority, the one with the highest IP address becomes the active router.

Description
Initialization: The router is in the process of starting up and is not yet ready to become the active router
Backup: The router is a backup router and is monitoring the active router
Master: The router is the active router and is forwarding traffic for the virtual router
Disabled: The router is not participating in VRRP and is not forwarding traffic

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