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Why are home networks prefixed with 192.168?

What makes the numbers 192.168 or 10. or 172.16 so special that those addresses, as opposed to other ones, were chosen as the private ipv4 ranges?

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marked as duplicate by random Aug 24 '11 at 21:26

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3 Answers 3

IPV4 defines 5 large IP addressing range classes:

  1. Class A: Starts at 0.0.0.0 finishes at 127.255.255.255
  2. Class B: Starts at 128.0.0.0 finishes at 191.255.255.255
  3. Class C: Starts at 192.0.0.0 finishes at 223.255.255.255
  4. Class D: Multicast, so its not defined.
  5. Class E: Reserved, not defined.

The private address ranges are based on the classes and are specified as a specific range over the start addresses of the 3 first classes:

  1. Class A: 24-bit Block (/8 prefix, 1 × A) starting with 10.0.0.0 ending at 10.255.255.255 gathering 16777216 different private addresses.
  2. Class B: 20-bit Block (/12 prefix, 16 × B) starting at 172.16.0.0 ending at 172.31.255.255 gathering 1048576 different private addresses.
  3. Class C: 16-bit Block (/16 prefix, 256 × C) starting at 192.168.0.0 ending at 192.168.255.255 gathering 65536 different private addresses.

You can find more details here.

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The Internet Engineering Task Force (IETF) directed the Internet Assigned Numbers Authority (IANA) to reserve the IPv4 address ranges. See this Wikipedia article on private networks.

Check out RFC1918.

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Nothing, really, it just worked out that way. There's one private block in each class. (See RFC 1918 for details on private IP addressing.)

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