VRRP Architectural Overview

VRRP Router

VRRP runs on each VRRP router and manages the state of the router. A host can have multiple VRRP routers configured, where each VRRP router belongs to a different virtual router.

A VRRP router has the following attributes:

• Router name – A system-wide unique identifier

• VRID – Identifies the virtual router within a LAN

• Primary IP address – Used as the source IP address of the VRRP advertisement

• Virtual IP addresses

• VRRP parameters – Includes priority, advertise interval, preempt mode, and accept mode

• VRRP state information and statistics

VRRP Processes

The following figure shows how VRRP works.

As shown in the preceding figure, VRRP works using the following components:

• Router rA is the master router for virtual router VRID 1 and the backup router for VRID 3. Router rA handles the routing of packets that are addressed to the VIP for VRID 1 and is ready to assume the routing role for VRID 3.

• Router rB is the master router for virtual router VRID 3 and the backup router for VRID 1. Router rB handles the routing of packets that are addressed to the VIP for VRID 3 and is ready to assume the routing role for VRID 1.

• Router rC does not have VRRP functions, but uses the VIP for VRID 3 to reach the client LAN subnet.

• Router rD is the master router for VRID 2. Router rF is the master router for VRID 5. Router rE is the backup router for both of these VRIDs. If rD or rF fails, rE becomes the master router for that VRID. Both rD and rF could fail at the same time. The fact that a VRRP router is a master router for one VRID does not preclude it from being a master router for another VRID.

• Router rG is the WAN gateway for the Backbone LAN. All of the routers attached to the backbone are sharing routing information with the routers on the WAN by using a dynamic routing protocol such as Open Shortest Path First (OSPF). VRRP is not involved in this, although router rC advertises that the path to the client LAN subnet is through the VIP of VRID 3.

• Router rH is the master router for VRID 10, and the backup router for VRID 11. Likewise, router rJ is them master router for VRID 11 and the backup router for VRID 10. This VRRP load-sharing configuration illustrates that multiple VRIDs can exist on a single router interface.

VRRP can be used as a part of a network design that provides almost total routing redundancy for all systems on the network.