Dr. Mark Humphrys

School of Computing. Dublin City University.

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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)
   Dublin, 9

   Netname: DCU-NET
   Netblock: -
i.e. room for 2562 = 65,536 addresses.

DCU addresses run from:     to:
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

IP address shows network class.

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

ancientbrain.com      w2mind.org      humphrysfamilytree.com

On the Internet since 1987.

Wikipedia: Sometimes I link to Wikipedia. I have written something In defence of Wikipedia. It is often a useful starting point but you cannot trust it. Linking to it is like linking to a Google search. A starting point, not a destination. I automatically highlight in red all links to Wikipedia and Google search and other possibly-unreliable user-generated content.