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It is a known fact that there are three blocks of IPv4 Addresses that were chosen to be reserved for private networks:
10.0.0.0 - 10.255.255.255 (10/8 prefix) 172.16.0.0 - 172.31.255.255 (172.16/12 prefix) 192.168.0.0 - 192.168.255.255 (192.168/16 prefix) (as specified by RFC 1918). However, although I can sort of see why 10.0.0.0 would be a natural choice, I can think of no particular reason why 172.16.0.0 and 192.168.0.0 were chosen among all the possibilities. I tried to google about this but got nothing, and the RFC document did not provide any explanation either. Was it really just a random decision?
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In August 2012, ARIN began allocating “172” address space to internet service, wireless, and content providers. There have been reports from the community that many network operators are denying access to devices having IP addresses from within the entire 172 /8 range. As a result, any device with a 172.
0.0 to 100.127. 255.255, netmask 255.192. 0.0) for use in carrier-grade NAT scenarios. This address block should not be used on private networks or on the public Internet.
And don't be surprised if you have a device or two at home with a so-called 192 IP address, or a private IP address beginning with 192.168. This is the most common default private IP address format assigned to network routers around the globe.
AS stated by ganeshh.iyer "
10.0.0.0/8 was the old ARPANET, which they picked up on 01-Jan-1983. When they shut down the ARPANET in 1990, the 10.0.0.0/8 block was freed. There was much argument about if there should ever be private IP spaces, given that a goal of IPv4 was universal to all hosts on the net.
In then end, practicality won out, and RFC 1597 reserved the now well known private address spaces. When ARPANET went away, the 10.0.0.0/8 allocation was marked as reserved and since it was known that the ARPANET was truly gone (the hosts being moved to MILNET, NSFNET or the Internet) it was decided that this was the best Class A block to allocate.
Note Class A. This was before CIDR. So, the Class A, B and C private address netblocks needed to come out of the correct IP ranges.
I know that 172.16.0.0/12 was picked because it offered the most continuous block of Class B (/16) addresses in the IP space that was in a reserved block. 192.0.0.0/24 was always reserved for the same reason that 0.0.0.0/8 and 128.0.0.0/16 were reserved (first blocks of the old Class C, A and B network blocks) so assigning 192.168.0.0/24 out as private fit well -- 192.0.2.0/24 was already TEST-NET, where you could use them in public documentation without fear of someone trying it (see example.com for another example.)"
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