IP CIDR Addressing Example
(Page 2 of 4)
First Level of Division
The pie is initially cut down the middle by using the single left-most host ID bit as an extra network bit. Let's see our network address block, 18.104.22.168/15 in binary, with the left-most host ID bit shown highlighted:
01000111 01011110 00000000 00000000
To make the split, we make one network equal to this binary network address with the highlighted bit remaining zero, and the other one with it changed to a one. This creates two subnetworksnot subnets as in the classful sense of the word, but portions of the original networkwhich I have numbered based on the numeric value of what is substituted into the new network ID bits:
Subnetwork #0: 01000111 01011110 00000000 00000000
Subnetwork #1: 01000111 01011111 00000000 00000000
Since bit #16 is now also part of the network address, these are /16 networks, the size of a classful Class B network. So, the subnetworks are:
Subnetwork #0: 22.214.171.124/16
Subnetwork #1: 126.96.36.199/16
Youll notice that the #0 subnetwork has the same IP address as the larger network it came from; this is always true of the subnetwork 0 in a network.
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