Virtual Router Redundancy Protocol (VRRP) is a networking protocol that automatically assigns routers that are available to handle inbound traffic. A detailed standard document for this protocol can be found at https://tools.ietf.org/html/rfc5798.

Keepalived uses VRRP to ascertain the current state of all the routers on the network. The protocol enables routing to switch between primary and backup routers automatically. The backup routers detect when the primary router becomes unavailable and then sends multicast packets to each other until one of the routers is "elected" as the new primary router A floating virtual IP address can be used to always direct traffic to the primary router. When the original primary router is back online, it detects the new routing state and returns to the network as a backup router.

The benefit of using VRRP is that you can rely on several routers to provide high availability and redundancy without requiring a separate software service or hardware device to manage this process. On each router, Keepalived configures the VRRP settings and ensures that the network routing continues to function correctly.

For more information, see https://www.keepalived.org/documentation.html, the /usr/share/doc/keepalived-version documentation, and the keepalived(8) and keepalived.conf(5) manual pages.