What is the custom subnet mask for a prefix length of /20?

What is the custom subnet mask for a prefix length of /20?

• A. 255.255.0.0
• B. 255.255.240.0
• C. 255.255.255.128
• D. 255.255.255.192

Answer: (B)

A prefix length of /20 indicates that the first 20 bits of the subnet mask are used for the network part, while the remaining bits are used for host addresses. In binary, a /20 subnet mask is represented as follows: 11111111.11111111.11110000.00000000 To convert this binary representation into decimal format, we break it down: - The first byte (8 bits) is all ones: 11111111 = 255 - The second byte is also all ones: 11111111 = 255 - The third byte begins with four ones followed by four zeros: 11110000 = 240 - The fourth byte is all zeros: 00000000 = 0 Putting this all together, the subnet mask for a /20 prefix length in decimal form is: 255.255.240.0 This subnet mask allows for a sufficient number of host addresses, specifically accommodating up to 4096 IP addresses within a single network (2^12 possible host addresses, where 12 bits are used for hosts in this subnet). Therefore, the custom subnet mask for a prefix length of /20 is accurately represented as 255.255.240.0.

A prefix length of /20 indicates that the first 20 bits of the subnet mask are used for the network part, while the remaining bits are used for host addresses. In binary, a /20 subnet mask is represented as follows:

11111111.11111111.11110000.00000000

To convert this binary representation into decimal format, we break it down:

• The first byte (8 bits) is all ones: 11111111 = 255

• The second byte is also all ones: 11111111 = 255

• The third byte begins with four ones followed by four zeros: 11110000 = 240

• The fourth byte is all zeros: 00000000 = 0

Putting this all together, the subnet mask for a /20 prefix length in decimal form is:

255.255.240.0

This subnet mask allows for a sufficient number of host addresses, specifically accommodating up to 4096 IP addresses within a single network (2^12 possible host addresses, where 12 bits are used for hosts in this subnet). Therefore, the custom subnet mask for a prefix length of /20 is accurately represented as 255.255.240.0.