| Classful addressing
(class A, class B, class C, etc) is now defunct. We no longer use
that terminology. The original model for distributing IP addresses,
based on classful addressing strategies did not take into account
the massive expansion of Internet use and was unable to scale to
meet this expansion. Classless Inter Domain Routing (CIDR) is now
a fundamental requirement for eligibility to receive IP address
space. All requests for address space must be supported by documentation
showing a technically justified need for the quantity requested
(that is, they must be used efficiently, according to best current
practice). Quantities of address space are now referred to by their
prefix length (or subnet mask). For example, /24 ("slash 24") refers
to 256 IP address numbers, or the equivalent of a former class C;
and /19 refers to 8,192 IP address numbers, or the equivalent of
32 former class Cs. |