HSRP (Hot Standby Router Protocol) uses a virtual MAC address for each group of routers participating in the protocol. The default virtual MAC address format for HSRP is 0000.0C07.ACxy, where xy is the HSRP group number in hexadecimal. For group 16, the hexadecimal equivalent is 10, resulting in the virtual MAC address 00:00:0c:07:ac:101. References: Cisco's official documentation on HSRP.