VRRP Overview

VRRP can prevent loss of network connectivity to end hosts if the static default IP gateway fails. By implementing VRRP, you can designate a number of routers as backup routers in the event that the default master router fails. VRRP fully supports Virtual Local Area Networks (VLANs) and stacked VLANs (S-VLANs).

Note: The term virtual router as defined in Configuring Virtual Routers in the JunosE System Basics Configuration Guide, is different from what is implied by VRRP. In this chapter, the term virtual router always refers to a VRRP router; that is, a router that has enabled VRRP.

In case of a failure, VRRP dynamically shifts the packet-forwarding responsibility to a backup router. VRRP creates a redundancy scheme that enables hosts to keep a single IP address for the default gateway but maps the IP address to a well-known virtual MAC address. VRRP provides this redundancy without user intervention or additional configuration at the end hosts.

The advantage of using VRRP is that you gain a higher availability for the default path without requiring configuration of dynamic routing or router discovery protocols on every end host.

VRRP routers viewed as a redundancy group share the responsibility for forwarding packets as if they owned the IP address corresponding to the default gateway configured on the hosts. At any time, one of the VRRP routers acts as the master, and other VRRP routers act as backup routers. If the master router fails, a backup router becomes the new master. In this way, router redundancy is always provided, allowing traffic on the LAN to be routed without relying on a single router.

A master always exists for the shared IP address. If the master goes down, the remaining VRRP routers elect a new master VRRP router. The new master forwards packets on behalf of the owner by taking over the virtual MAC address used by the owner.

When implemented in your network, VRRP interprets any active link to a subnet to indicate the router has access to the entire subnet. VRRP leverages the broadcast capabilities of Ethernet. Provided that one of the routers in a VRRP configuration is running, ARP requests for the IP addresses assigned to the default gateway always receive replies. Additionally, end hosts can send packets outside their subnet without interruption.

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