Configuring Layer 3 Redundancy with Virtual Router Redundancy Protocol – VRRP and Gateway Load Balancing Protocol – GLBP
What is GLBP?

While HSRP and VRRP provide gateway resiliency, the standby members of the redundancy group along with their upstream bandwidth is not used while the device is in standby mode. Only the active router for the HSRP and VRRP group forwards traffic for the virtual MAC. Resources associated with the standby router are not fully utilized. Some load balancing can be accomplished with these protocols through the creation of multiple groups and through the assignment of multiple default gateways, but this configuration creates administrative burden.

Cisco designed Gateway Load Balancing Protocol (GLBP) to allow automatic selection and simultaneous use of multiple, available gateways, as well as automatic failover between those gateways. Multiple routers share the load of frames that, from a client perspective, are sent to a single default gateway address. With GLBP, resources can be fully utilized without the administrative burden of configuring multiple groups and managing multiple default gateway configurations as is required with HSRP and VRRP.