Gateway load balancing (GLBP)
A first-hop redundancy variant (Cisco GLBP) where several gateways are active at once and share the traffic load — unlike HSRP/VRRP where only one router does the work and the rest wait in standby. Redundancy plus load sharing at the same time.
Mechanic: an "Active Virtual Gateway" (AVG) hands out different virtual MAC addresses to clients when they ARP for the shared virtual IP — different clients get different routers' MACs and thereby send their traffic to different physical gateways. All participate in forwarding (Active Virtual Forwarders) while redundancy remains (if one fails, another takes over its MAC). Win over HSRP/VRRP: the upstream bandwidth and load are spread over several routers instead of one doing everything while the others are idle. Downside: Cisco-proprietary (VRRP is the open standard, but without built-in load sharing). A more advanced FHRP when you want to use all upstream capacity. Related to first-hop redundancy and HSRP.