Registered Class C addresses
Howard C. Berkowitz
hcb at clark.net
Fri Dec 18 17:58:22 UTC 1998
At 11:56 AM -0500 12/17/98, Peter Polasek wrote:
>I apologize in advance if this is an ISP 101 question. Is there
>any reasonable method for acquiring a registered Class C address
ISPs have to start somewhere! Let me suggest rephrasing the question a
bit. No one can get class A, B, or C addresses any longer, because the
concept of "classful" addresses is dead. Address space allocation is on a
CIDR block basis, where a class C would be equivalent to a /24, a class B
to a /16, and a class A to an /8.
If you need the equivalent of two class C blocks, your requirement is for a
/23 CIDR block. A starting point is Hank Nussbacher's CIDR FAQ at
We are opening a data center in England and need at
>least 2 registered Class C addresses IP for the production network.
>Last time I checked, subnetted class C registered addresses were
>still available (within the Class A range), but pure Class C addresses
>were not. We very strongly prefer to avoid subnetting addresses because
>this becomes extremely difficult maintain when the network becomes large
>(as this will).
See RFC2050, the policy for address allocation. I doubt that any address
registry would consider a request for address space that is not subnetted
because it is inconvenient to maintain.
Take a look at my tutorial at the last NANOG meeting, which is on the NANOG
web site at http://www.nanog.org/mtg-9811/ppt/berk/index.htm. I describe
some approaches to semi-automating ISP address space management.
For a somewhat broader look, I've just published a book that deals with
address justification and planning, _Designing Address Architectures for
Routing & Switching_ (Macmillan Technical Publishing ISBN #1-57870-059-0).
Major online and physical bookstores just started making it available,
although Amazon is correcting the title.
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