When a first hop redundancy solution is designed, which protocol ensures that load balancing occurs over multiple routers using a single virtual IP address and multiple virtual MAC addresses?

GLBP is specifically designed to allow multiple physical routers to act as active forwarders for a single virtual IP address, achieving load balancing by having the GLBP Active Virtual Gateway (AVG) respond to ARP requests with different virtual MAC addresses for each active forwarder.

IRDP (ICMP Router Discovery Protocol) is a legacy protocol for hosts to discover routers; it does not provide redundancy or load balancing for first-hop gateways.

VRRP (Virtual Router Redundancy Protocol) provides redundancy by electing a master router, but traffic typically flows through a single active router using a single virtual IP and MAC address, with others in standby.

HSRP (Hot Standby Router Protocol) provides redundancy by electing an active and a standby router, but traffic generally flows through a single active router using one virtual IP and MAC address for a given group.