What IP addresses are subnetted A 139.233.12.12 255.255.255.0 B 10.0.0.1 255.255.255.0 C 192.168.0.1 255.255.255.0 D 190.233.17.3 255.255.255.0?

Answer 1

A, B and D are subnets. C is not.

IP addresses A and D are both Class B subnets. Class B addresses normally have a subnet mask of 255.255.0.0. The first two bits of a class B network are always 10 which leaves 14 bits for the network prefix, thus allowing up to 16,384 separate Class B networks (including 139.233.0.0 and 190.233.0.0). The last 16 bits denote the host number thus there can be up to 65,536 hosts per network. By specifying a subnet mask of 255.255.255.0 the network can be divided into as many as 256 separate subnets each with 256 hosts.

IP address B is a Class A subnet. Class A addresses normally have a subnet mask of 255.0.0.0. The first bit of a class A network is always 0, which leaves 7 bits for the network prefix, thus allowing up to 127 Class A networks (including 10.0.0.0). The last 24 bits denote the host number thus there can be up to 16,777,216 hosts per network. By specifying a subnet mask of 255.255.255.0, the hosts can be divided into as many as 65,536 separate subnets each with up to 256 hosts.

IP address C is a Class C address, but is not a subnet. Class C addresses normally have a subnet mask of 255.255.255.0. The first three bits in a Class C network are always 110, leaving 21 bits for the network prefix, thus allowing up to 2,097,152 Class C networks (including 192.168.0.0). The last 8 bits denote the host number thus there can be up 256 hosts per network. To make a subnet out of a Class C address you must have a subnet mask of 255.255.255.X, where X may be 192, 224, 240, 248 or 252. That is, 2, 3, 4, 5 or 6 bits to denote the subnet and the remaining bits to denote the hosts. Thus a subnet mask of 255.255.255.192 would allow as many as 4 subnets each with up to 64 hosts, while a subnet mask of 255.255.255.240 would allow as many as 16 subnets each with up to 16 hosts.

It should be noted that the maximum number of hosts is actually 2 less than the figures shown above. This is because the host address with all 0 bits is reserved for network address while the host address with all 1 bits is reserved for broadcasting.