Some sources say that class A IP addresses start at 126.96.36.199, and some say 0.0.0.0. I have also heard that 0.0.0.0 is a special kind of IP address. So is 0.0.0.0 a class A IP address or not?
closed as off topic by ThatGraemeGuy, Hyppy, Shane Madden♦, Ward♦, Scott Pack May 20 '11 at 13:25
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http://tools.ietf.org/html/rfc3330 Explains it.
0.0.0.0/8 - Addresses in this block refer to source hosts on "this" network. Address 0.0.0.0/32 may be used as a source address for this host on this network; other addresses within 0.0.0.0/8 may be used to refer to specified hosts on this network [RFC1700, page 4].
So it is Class A but a special adress also.
0.0.0.0 is a special address, it is even network (0.0.0.0/32 and so on),that acts like loopback 127.0.0.1 (that is only for local machine), but is accessible for anyone outside. It acts like a default route.
A number of network addresses are reserved for special purposes. 0.0.0.0 and 127.0.0.0 are two such addresses. The first is called the default route, and the latter is the loopback address. The default route has to do with the way the IP routes datagrams.
They arent A B C D or even E.
0.0.0.0 is the default route
But there is the question is what class and there is answers, choose class A.
The address 255.255.255.255 is used as broadcast addresses and 0.0.0.0 as a default route address, meaning any network.