The origin of the private network address 192.168.*.*

ipnetworkingprivate

I had a smart (but non-technical) user ask me today:

Why did they pick 192.168.. for a private network address?

The only answer I could come up with is because 192 = 11000000 in binary. And 168 is 10101000 in binary. Both of which are kind of cool looking.

Is there a real historical reason for that particular choice of numbers? Why not 127.127..? Or 128.128..?

Similar question for
10.0.0.0
and
172.16.0.0

Thanks!

Best Answer

Before classless networks were invented, it was decided to make three ranges of private addressing space. These were:

  • Class A: 10/8 (the old ARPA reservation)
  • Class B: 172.16/12 (one of the first available class Bs)
  • Class C: 192.168/16 (one of the first available class Cs)

There are:

  • 1 Class A private prefixes (16.7 million addresses)
  • 16 Class B privates (65536 addresses each, totalling ~1 million addresses)
  • 256 Class C privates (256 addresses each, totalling 65536 addresses)

It is important to note that "Classes" haven't existed since 1994, and these days we use CIDR, which has a variable length subnet mask.

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