Network classes

The old way of handing out IP addresses.

Summary from here.

Example - DCU's block of addresses

DCU has the following block of addresses:

Dublin City University (NET-DCU-NET)
   Glasnevin
   Dublin, 9
   IE

   Netname: DCU-NET
   Netblock: 136.206.0.0 - 136.206.255.255

i.e. room for 256² = 65,536 addresses.

DCU addresses run from:
136.206.0.0 to:
136.206.255.255
In binary, from:
1000 1000 1100 1110 0000 0000 0000 0000 to:
1000 1000 1100 1110 1111 1111 1111 1111
See IP decimal-binary table

First 16 bits are the DCU network number 136.206.
This is in binary:
1000 1000 1100 1110
Second 16 bits are the host number on that network.

This is a Class B network.
To be precise, the leading 10 indicates Class B, then the network number is the 14 bit:
00 1000 1100 1110
So a DCU address is:
Class B identifier, DCU network, machine number n:
10 00 1000 1100 1110 nnnn nnnn nnnn nnnn

CCNA Tutorial
- IP decimal-binary table

IP address shows network class.

Special IP addresses.
See Reserved IP addresses and Private network.