CompTIA Network+ (N10-009) — Question 98

A security administrator is creating a new firewall object for a device with IP address 192.168.100.1/25. However, the firewall software only uses dotted decimal notation in configuration fields. Which of the following is the correct subnet mask to use?

Answer options

• A. 255.255.254.0
• B. 255.255.255.1
• C. 255.255.255.128
• D. 255.255.255.192

Correct answer: C

Explanation

The correct subnet mask for a /25 network is 255.255.255.128, which allows for 126 usable host addresses. The other options do not correspond to a /25 subnet; A (255.255.254.0) is for a /23, B (255.255.255.1) is not a valid subnet mask, and D (255.255.255.192) is for a /26, which is smaller than /25.