Which class has no valid host addresses because it is used for multicast?

• A. Class D
• B. Class A
• C. Class B
• D. Class C

Answer: (A)

Multicast addressing is about delivering a packet to multiple receivers that join a group. In IPv4, Class D is reserved for multicast, covering the range 224.0.0.0 to 239.255.255.255. Because these addresses identify a group rather than a single host, there aren’t valid host addresses within this class. Packets sent to a multicast address are replicated and delivered to all devices that have joined the corresponding multicast group. The other classes (A, B, and C) are used for unicast addressing, where each address points to a specific host with a dedicated host portion.