I am sure that David Gillette will jump in on this one and give a more
detailed explanation, but I will start with some basic answers. The
assignment of "external" IP addresses is coordinated by central authorities.
It is more complex now than in the earlier days of the Internet. See the
following sites for information:
http://www.internic.net/
http://www.iana.org/ipaddress/ip-addresses.htm

Originally, there were classes of IP with A giving you a range of over 16
million addresses. A class B would give you 64k addresses, and class C had
256 (254 usable - separate topic). There are also class D and E designations
primarily for test purposes.

Because the Internet grew so quickly, the IP addresses were becoming scarce.
The classes of A, B, and C gave way to CIDR (Classless Inter-Domain Routing)
where ranges of IP addresses are assigned without regard to class.

For a local network where the computers are not directly connected to the
Internet, several ranges of IP addresses have been designated as "internal"
and not routable over the Internet. That is, the Internet backbone routing
equipment will discard any addresses that are in one of these internal
values. The internal ranges are:
10.n.n.n
90.0.0.n
172.16.n.n through 172.31.n.n
192.168.n.n
And 169.254.n.n known as APIPA (Automatic Private IP Addressing)
The "n" indicates that any number (0-255) may be used in that position.
There is also 127.0.0.n that is reserved as the loopback address - that is,
if your computer uses IP, then it automatically includes 127.0.0.1 as its
own address - you may ping 127.0.0.1 to check your own computer's response.

Hope this helps some. There is much more to this, but not appropriate in one
answer.

Peter
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The NoSpin Group
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> -----Original Message-----
> I am new to networking and I have a question on IP addressing. I know
> there are 3 classes of IP addresses; A, B, and C. My question is who
> assigns these addresses so that every computer has a unique address?
>
> Chilangisha Changwe

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