GLBP (Gateway Load Balancing Protocol) is a Cisco proprietary protocol that allows you to create a virtual gateway IP address between two or more routers. The advantage of having a virtual gateway address is that most host devices like computers or printers can only be configured with a single default gateway. If you use the physical IP address of a single router as the default gateway then those hosts will be unable to get out of their own subnet once the router fails. GLBP elects one AVG (Active Virtual Gateway), all other routers become backup members. The AVG then assigns a virtual MAC address to each member of the GLBP group, called AVFs (Active Virtual Forwarders). Each AVF will forward packets that are destined to the virtual MAC address. These lessons explain how GLBP works and how to configure GLBP.