What is the netmask for a CIDR /23 subnet?

The netmask for a CIDR /23 subnet is 255.255.254.0. In CIDR (Classless Inter-Domain Routing) notation, the number following the slash represents the number of bits set to '1' in the subnet mask.

For a /23 subnet, this means that the first 23 bits of the subnet mask are '1's, and the remaining 9 bits are '0's. When translated to decimal, the bit representation of the subnet mask would look like this:

• The first 8 bits (255): 11111111 (all bits are '1')
• The second 8 bits (255): 11111111 (all bits are '1')
• The next 7 bits (254): 11111110 (the first 7 bits are '1', the last bit is '0')
• The last 8 bits (0): 00000000 (all bits are '0')

Putting these together yields the decimal representation of 255.255.254.0, which is the correct netmask for a /23 subnet.

In contrast, the other options do not accurately represent the required 23 '1' bits:

• 255.255.