Why are the address ranges 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 reserved?

Question

I'm just curious... Why are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 reserved for private networks? These ranges seem arbitrarily chosen. Why were they chosen, instead of, say, 128.0.0.0/8, which doesn't seem as random?

Answer 1

These address ranges were set aside as private network addresses.  This means that these IP addresses will not traverse the internet.  For example, if I worked at a business that had 500 pcs and servers, I could set them up on a private network using one of the sets of private ip address ranges.  All my pcs and servers could communicate using the private ip addresses and I don't have buy unique ip addresses for each pc or server.  This allows me to buy one public ip address and to the outside world (the internet), my entire network looks like one ip address.

Answer 2

I don't know the wisdom of the designers or why they made these decisions.  They may well be arbitrary as you suggest.

Answer 3

Those are private Ip address and are "un-routable". That way you can use them inside a private network and no one will be able to send information directly to your address. Also, it allows for all or most private networks to re-use those same numbers because all of the inside/private addresses are translated into just 1 public IP address when they leave the network to travel the "net". If there were no private ip addresses, and everything on the internet required thier own "public" IP, we would have run out of IP addresses long, long ago.

Example: A big company using a private class A scheme like 10.*.*.*  could have 16,000,000 computers all use just one public IP address, instead of taking up all those public addresses.

IP addresses are running out anyway, henceforth the introduction of IPv6