VRPP (Virtual Router Redundancy Protocol)
An IETF specification designed to bring resiliency and redundancy to Layer 3 routers and switches that are run as statically configured default gateways.
When VRRP is turned on, one of its first duties is to provide the master router with a virtual media access control (MAC) address, one that can be taken over by the next-in-line backup.
MAC resides at OSI Layer 2 and represents a device's physical identification; switches know where to forward IP packets by relating the IP address to the MAC address of the next-hop switch or router. By employing a virtual MAC address, VRRP ensures that end systems won't need to change their default-gateway address in the event of failover. In fact, end systems won't notice that a backup has taken over for the master.
Key to VRRP's operation is a process in which the master router sends a special VRRP packet, known as an advertisement, to the backups. Advertisement intervals can be set by the user; the VRRP default is 1 second.
If the advertisements suddenly stop, the backups set interval timers, typically for three times the advertisement frequency.
If no further advertisements appear, the backups assume the master is down and the failover routine is activated. From that point, the election of the next-in-line master typically takes less than a second.
Meanwhile, each router must report its status regularly to the network management console via SNMP. Network management may also be alerted if the VRRP packets show anomalies in any other areas - for instance, if a normal handshaking error occurs or authentication fails.
Although it is a relatively simple protocol, VRRP is effective protection for networks with statically configured gateways. And while some end systems employ discovery tools for locating new gateways in case of failure, VRRP represents a far more efficient solution to the problem - VRRP applies intelligence to the network rather than to the end system. Compared with the alternative - setting and managing individual discovery protocols in each of the network's end systems - VRRP is an efficient, simple technology.
From Bringing redundancy to Layer 3 switching, Network World Tech Update, 12/14/98.
Additional resources
IETF VRPP working group
Draft VRRP spec
Would replace RFC 2338, on which the above information is based.
Routers/switches research center
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