The most common private ranges, defined by RFC 1918, are

10.x.x.x (1 Class A network)
172.16.x.x - 172.31.x.x (16 Class B networks)
192.168.x.x (256 Class C networks)

  APIPA (169.254.x.x (Class B)) is a special case defined elsewhere, as is
(I believe) 192.0.2.x (Class C).  I'm not sure where, or even if, 90.x.x.x
is defined.

  RFC 1918 and APIPA are unlikely to change before we all move to IPv6
(i.e., don't hold your breath).  The other ranges mentioned *may* be safe to
use today, but are used sufficiently rarely that they may be subject to
reclamation for public use -- you shouldn't need more than RFC 1918 for even
a rather substantial network.

David Gillett (no final e...)


On 27 Jan 2005 at 9:37, Peter Shkabara wrote:

> 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
> -----------------------------------------------
> The NoSpin Group
> [log in to unmask]
>
> > -----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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