Appendix G: VRRP
Virtual Router Redundancy Protocol (VRRP) is designed to eliminate the single point of failure inherent in the
static default routed environment . In a VRRP environment, two or more "virtual" routers cooperate to provide
a high-availability capability on a LAN . VRRP specifies an election protocol that dynamically assigns routing
responsibility to one of the virtual routers on a LAN .
A virtual router consists of a set of router interfaces on the same network that share a virtual router identifier
(VRID) and a virtual IP address . One router in the group becomes the VRRP Master and the other routers are
designated as VRRP Backups . The VRRP Master controls the IP addresses associated with a virtual router .
The VRRP Master router periodically sends advertisements to a reserved multicast group address . The VRRP
Backup routers listen for advertisements, and one of the Backups will assume the Master role, if necessary . A
VRRP router can support many virtual router instances, each with a unique VRID/IP address combination . The
election process provides dynamic failover to one of the remaining VRRP Backups should the Master become
The virtual IP address shared by a group of VRRP routers on a given network segment functions as the next-
hop IP address used by neighboring hosts . The VRRP Master router simply forwards packets that have been
received from hosts using the VRRP Master as the next-hop gateway . The existence of a VRRP Master and one
or more VRRP Backups is transparent to the neighboring hosts .
The advantage gained from using VRRP is a default path with higher availability, but without requiring
configuration of dynamic routing or router discovery protocols on every end host .
VRRP on HP ProCurve switches is interoperable with other routers that support RFC 3768 .
VRRP operational aspects include:
• Preempt delay timer to allow other protocols to complete their convergences
• Preemptive mode can be disabled to prevent VRRP router flapping
• Default Advertisement interval of 1 second
• Default Detection time of 3.6 seconds