In a Class B address, what is the significance of the first bit?

• A. It must always be turned off.
• B. It must always be turned on.
• C. It indicates a private address.
• D. It indicates a public address.

Answer: (B)

In IPv4, classful addressing uses the first bits of the address to identify its class. For Class B, the leading bits are 10, which means the first bit is always 1. That single bit being on is how Class B addresses are distinguished from other classes, and it aligns with the address range 128.0.0.0 to 191.255.255.255, where the first bit must be 1. This characteristic is inherent to the class and helps define the default network portion (the first 16 bits) and routing behavior under classful rules. It does not indicate private versus public status; private addresses are defined by RFC 1918 and can appear within Class B ranges, so the first bit isn’t a privacy flag.