N10-005 Question #625: Real Exam Question with Answer & Explanation

The correct answer is B: 255.255.0.0. Class B IP addresses (128.0.0.0 to 191.255.255.255) use a default subnet mask of 255.255.0.0, reserving the first two octets for the network and the last two for hosts.

Question

Which of the following is the default subnet mask for a Class B address?

Options

A255.0.0.0
B255.255.0.0
C255.255.255.0
D255.255.255.255

Explanation

Class B IP addresses (128.0.0.0 to 191.255.255.255) use a default subnet mask of 255.255.0.0, reserving the first two octets for the network and the last two for hosts.

Common mistakes.

A. 255.0.0.0 is the default subnet mask for Class A addresses (1.0.0.0 to 126.255.255.255), which use only the first octet for the network portion.
C. 255.255.255.0 is the default subnet mask for Class C addresses (192.0.0.0 to 223.255.255.255), which use the first three octets for the network portion.
D. 255.255.255.255 is a host route mask used to identify a single specific host address, not a default classful network mask for any address class.

Concept tested. Classful IP addressing default subnet mask for Class B

Reference. https://learn.microsoft.com/en-us/troubleshoot/windows-client/networking/tcpip-addressing-and-subnetting

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