What is the virtual MAC address format for HSRPv1?

The correct format for the virtual MAC address in HSRPv1 (Hot Standby Router Protocol version 1) is indeed represented as 0000.0c07.acXX. HSRPv1 uses a well-defined method for generating virtual MAC addresses, where the first 24 bits (0000.0c) are a prefix that identifies it as an HSRP address, followed by specific bits that represent the HSRP group number.

In this case, "07" comes from the HSRP group identifier, and "ac" is a constant for HSRPv1, while the last two digits (represented as XX) are used to represent the actual group number. Therefore, the structure directly addresses how HSRP manages redundancy among routers.

This specific format is essential for network devices to recognize the MAC address as belonging to a virtual router created by HSRP, allowing them to appropriately forward packets to the active router. Understanding this format is crucial for anyone working with HSRP in network design and troubleshooting to ensure proper connectivity and redundancy.