Which IP address is valid for a host?

Question

Options

• A127.0.0.255
• B45.0.0.0
• C255.124.30.4
• D132.105.122.1

• A
  8% (2)
• B
  4% (1)
• C
  4% (1)
• D
  83% (20)

Explanation

132.105.122.1 falls in the Class B range (128–191 first octet) with no special restrictions - all octets are valid, and neither the host nor network portion is all zeros or all ones, making it fully assignable to a host.

Why the others fail:

• A (127.0.0.255): The entire 127.0.0.0/8 block is reserved for loopback - traffic sent here never leaves the local machine and cannot be assigned to a network host.
• B (45.0.0.0): The last octet of .0 with a classful mask means the host portion is all zeros, which identifies the network address itself - not an individual host.
• C (255.124.30.4): A first octet of 255 places this in Class E (240–255), reserved for experimental use and never assigned to hosts.

Memory tip: Think "127 loops back, .0 is the network, .255 broadcasts (or Class E), and 224+ is multicast/experimental" - any address hitting those rules is off-limits for a host.

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