On 4 Apr 2007, in the Usenet newsgroup comp.protocols.tcp-ip, in article
<1175717399.325660.311410@n59g2000hsh.googlegroups .com>, Doug wrote:

>Typically when a company gets internet access for all of the nodes in
>the company, do they get a subnet and network, or a whole network in
>an address class (or multiple networks in an address class, so they
>can supernet).

2050 Internet Registry IP Allocation Guidelines. K. Hubbard, M.
Kosters, D. Conrad, D. Karrenberg, J. Postel. November 1996.
(Format: TXT=28975 bytes) (Obsoletes RFC1466) (Also BCP0012)
(Status: BEST CURRENT PRACTICE)

4632 Classless Inter-domain Routing (CIDR): The Internet Address
Assignment and Aggregation Plan. V. Fuller, T. Li. August 2006.
(Format: TXT=66944 bytes) (Obsoletes RFC1519) (Also BCP0122)
(Status: BEST CURRENT PRACTICE)

RFC2050 would be a good place to start - you'll have to come up with an
idea of how much address space you need. Depending, you _might_ get it
from a Regional, National, or Local Internet registry - or perhaps from
an Internet Service Provider. Classful (Class A, B, C, etc) hasn't been
a term of reference since the early 1990s, with RFC4632 being the current
document.

>If they do get a subnet, is it possible to re-subnet? Maybe, for
>example, I have a subnet with so many addresses, but I want to make
>more subnets out of that subnet for security or efficiency reasons. Is
>that done?

Typically, you'll get a block of addresses. How you may divide these up
behind your perimeter gateway is (within reason) your decision. If
yourcompany.example.com gets a block of (example) 768 addresses, your
upstream will be routing packets in that range to your router, but as
768 isn't a binary number, you will possibly be breaking that up behind
the perimeter into usable chunks - perhaps 3 /24 or 6 /25 or something
similar.

>Or, do you have to just buy networks assigned by address class?

Classful hasn't been available for over 14 years - though you may be
assigned a /16 (former Class B) if there is a demonstrated need. As of
the middle of last month, the five RIRs (AFRINIC, APNIC, ARIN, LACNIC
and RIPE) had allocated/assigned some 2.45 billion addresses world wide
(about 66.1 percent of available IPv4 address space) in 79300
assignments in 209 sized blocks from 26 to 9175040 addresses. Most
computers (really a function of the operating system) want networks
sized on a power of two - see the tables in RFC1878 as examples.

Old guy