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So there are A,B,C,D,E ranges like 1-126, etc... but in an IP address, what means 192 out of 192.168.12.4? Is it a class A block or what? I have trouble understanding. Thanks.

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migrated from stackoverflow.com Sep 22 '10 at 1:56

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1 Answer 1

Classful routing hasn't been done since 1993 - so this class A, B, C junk doesn't mean much anymore. Nowadays, there is Classless Inter-Domain Routing (CIDR). Regardless, an IPv4 address is just a 32-bit number. It's broken down into 8-bit chunks and printed in decimal in the dot notation for your human brain's convenience, but it doesn't mean anything in reality. All that 192 means is that the first 8 bits of your IP address are 11000000.

Your IP address is a bit of a special case, in that it's part of the 16-bit private network range for IPv4 (192.168.0.0 to 192.168.255.255).

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The third response on the above question covers classes. 192.0.0.0/8 would be a class A size block, but 192 is in the old class C range. –  BillThor Sep 22 '10 at 2:52
    
A couple of ranges are reserved for private use, as described in faqs.org/rfcs/rfc1918.html and are not routed on the internet. 192.168.x.x, 172.16.x.x (actually 172.16.x.x - 172.31.x.x) and 10.x.x.x are private ranges. 192.x.x.x by itself isn't. –  Wouter de Bie Sep 22 '10 at 6:28

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