What MAC address does the active router use to respond to ARP requests in an FHRP setup?

In a First Hop Redundancy Protocol (FHRP) setup, such as HSRP (Hot Standby Router Protocol), VRRP (Virtual Router Redundancy Protocol), or GLBP (Gateway Load Balancing Protocol), the active router uses a virtual MAC address to respond to ARP requests. This virtual MAC address is associated with the virtual IP address of the gateway that the routers are presenting to the clients.

When a client sends an ARP request to resolve the IP address of the default gateway, the active router responds using this virtual MAC address, ensuring that all hosts on the local network will correctly learn the address that will be used for forwarding packets to the gateway, regardless of which router is currently active. This virtual addressing scheme provides redundancy and failover capabilities, as if the active router fails, the standby router can take over and utilize the same virtual MAC address to maintain connectivity.

Other types of MAC addresses, such as the physical MAC address of a router, are specific to that device and do not provide the same failover capabilities. The standby MAC address would not be used for responding to ARP requests because that address is only for the standby router, and a broadcast MAC address is not applicable in this scenario since it's used