Subnetting Question

adrianm68

Go this one wrong because I looked at the wrong octet and stupidly thought someone would design a network with no hosts. But when I saw the answer, I wanted to get clarification, since I think the total number of hosts per subnet should be 509. There are 9 bits for hosts = 511 ip addresses. Take 2 off for subnet id and broadcast = 509.

Where am I wrong?

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rob42

First, note that this is a ‘Class B’ IP and as such the standard Mask (255.255.0.0) would give us 16 bits for the Subnets and 16 bits for the Nodes.

But, the Mask used is 255.255.254.0 which has allocated an extra 7 bits for the Subnets, therefore 7 bits less for the Nodes.

16-7 = 9 bits for the Nodes

2^9 = 512 Nodes, less two = 510.

2^7 = 128 Subnet.

{Sorry, that should read "128 Subnets."}