Re: Stupid Question maybe?

[William Herrin <bill () herrin us>]

On Mon, Dec 17, 2018 at 9:36 PM Joe <jbfixurpc () gmail com> wrote:
> Apologizes in advance for a simple question. I am finding conflicting
> definitions of Class networks. I was always under the impression
> that a class "A" network was a /8 a class "B" network was a /16
> and a class "C" network was a /24. Recently, I was made aware
> that a class "A" was indeed a /8 and a class "B" was actually
> a /12 (172.16/172.31.255.255) while a class "C" is actually a /16.

Hi Joe,

Take everything you've ever heard about classful networking, throw it
away, and outside of trivia games never think about it again. Network
address classes haven't been a valid part of TCP/IP for more than two
decades now.

For historical trivia purposes only, the CIDR /16 replaced class B.
Had RFC 1918 come out before CIDR (RFC 1519),
172.16.0.0-172.31.255.255 would have described 16 contiguous class
B's, not just one, while 192.168.0.0-192.168.255.255 would have
described 256 contiguous class C's. In fact, this terminology is used
in RFC 1918's predecessor, RFC 1597.

And if you really like trivia, find the math error in RFC 1597.

Class A started at 0.0.0.0, class B started at 128.0.0.0 and class C
started at 192.0.0.0. There was also a class D (now the multicast
address space) starting at 224.0.0.0 and a class E (still reserved)
starting at 240.0.0.0.

Regards,
Bill Herrin



-- 
William Herrin ................ herrin () dirtside com  bill () herrin us
Dirtside Systems ......... Web: <http://www.dirtside.com/>