What subnet mask is needed if an IPv4 network has 40 devices that need IP addresses and address space is not to be wasted?

  • 255.255.255.224
  • 255.255.255.128
  • 255.255.255.240
  • 255.255.255.192
  • 255.255.255.0
Explanation & Hint:

To determine the subnet mask needed for a network with 40 devices, you need to calculate the subnet size that can accommodate at least 40 hosts. Remember that in a subnet, two IP addresses are reserved: one for the network address and one for the broadcast address. So, you need a subnet with at least 42 addresses.

Here’s how the subnet masks correspond to the number of addresses they provide:

  • 255.255.255.224 – This is a /27 subnet mask, which provides 32 addresses (30 usable for hosts).
  • 255.255.255.240 – This is a /28 subnet mask, which provides 16 addresses (14 usable for hosts).
  • 255.255.255.192 – This is a /26 subnet mask, which provides 64 addresses (62 usable for hosts).
  • 255.255.255.128 – This is a /25 subnet mask, which provides 128 addresses (126 usable for hosts).
  • 255.255.255.0 – This is a /24 subnet mask, which provides 256 addresses (254 usable for hosts).

The smallest subnet mask that can accommodate at least 42 addresses is 255.255.255.192, which is a /26 subnet mask. This will allow for 62 usable IP addresses, which is more than enough for 40 devices without wasting too much address space.

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