HSRP (Hot Standby Router Protocol) is a Cisco proprietary redundancy protocol for establishing a fault-tolerant default gateway. The protocol establishes a framework between network routers to achieve default gateway failover if the primary gateway becomes inaccessible. HSRP group 37 uses the virtual MAC address 00:00:0c:07:ac:25 by default. This address is derived from the HSRP group number, which in this case is 37. The MAC address is composed of the Cisco OUI (Organizationally Unique Identifier), which is 00:00:0c, followed by the fixed HSRP identifier 07:ac, and finally the HSRP group number in hexadecimal format, which for group 37 is 25 in hexadecimal.