Final answer:
The Cisco-proprietary FHRP that elects an AVG and up to four primary AVFs is GLBP, which differs from HSRP and VRRP.
Step-by-step explanation:
The Cisco-proprietary First Hop Redundancy Protocol (FHRP) that elects an Active Virtual Gateway (AVG) and up to four primary Active Virtual Forwarders (AVFs) is Gateway Load Balancing Protocol (GLBP). GLBP allows for automatic selection and simultaneous use of multiple available gateways in addition to the automatic failover between them. This differs from Cisco's Hot Standby Router Protocol (HSRP), which elects a single active router and one or more standby routers, and the Virtual Router Redundancy Protocol (VRRP), which operates similarly to HSRP but is an open standard. Lastly, Link Aggregation Control Protocol (LACP) does not elect AVGs or AVFs as it is used for bundling multiple network links together for redundancy and increased throughput.