What is the subnet mask for Class A addresses?

The subnet mask for Class A addresses is 255.0.0.0. Class A IP addresses are designed for large networks, and the allocation of address space reflects this by allowing for a significant number of host addresses.

In this classification, the first octet (the first set of numbers) is reserved for network identification, while the remaining three octets can be used for host addresses within that network. The subnet mask of 255.0.0.0 effectively means that the first 8 bits (one octet) of an IP address are the network part, and the remaining 24 bits are reserved for host addresses, allowing for over 16 million possible addresses in a single Class A network.

This structure is designed to accommodate the needs of very large organizations and is fundamental in the organization of IPv4 addressing for scalable networking.