inet hosts question
vince at unsane.co.uk
Fri Nov 14 08:50:42 PST 2008
Matthew Seaman wrote:
> Vincent Hoffman wrote:
>> Gary Hartl wrote:
>>> I thought I could do it by using the /class ie /32 for class c but i
>>> remember what the class delegation is for that size of pool, I think
>>> it is a
>>> class B.
>> 192.168.0.0/16 for your example.
>> and yes this is a class B (not all /16s are though.)
>> the /x notation is called CIDR (classless interdomain routing.)
> Class C surely? 192.168.0.0/16 is the RFC1918 Class C reserved
> range of 256 /24 networks.
Doh yes indeed. no idea why i said B. not the stupidest thing i've said
today either ;)
> Yes, Class B networks were /16s, but the A, B, C... classification
> is derived from the number of leading 1's in the binary representation
> of the first octet of the address, not the netmask. Thus
> Binary: Decimal: Class: Used for:
> 0000 0000 -- 0111 1111 (0 - 127) Class A /8 Networks
> 1000 0000 -- 1011 1111 (128 - 191) Class B /16 Networks
> 1100 0000 -- 1101 1111 (192 - 223) Class C /24 Networks
> 1110 0000 -- 1110 1111 (224 - 239) Class D Multicast
> 1111 0111 -- 1111 1111 (240 - 255) Class E Reserved, experimental
> Hence the first /half/ of the address space was reserved for class A
> network allocations (16777214 hosts per net) and half of the rest was
> reserved for class B allocations (65534 hosts per net). Some large
> Universities probably could justify a Class B allocation, but I don't
> think any single institution or body has ever put enough machines onto
> the Internet to justify having a whole Class A network to themselves
> according to modern criterea.
> Needless to say, this was incredibly wasteful scheme in terms of
> address space coverage. As the whole 'network class' thing was an
> early attempt to just shave a few bytes of RAM in internet routers by
> not having to store explicit netmasks -- an economy that was rapidly
> made obsolete by the falling cost and increasing capacity of hardware
> -- class based allocation is now completely obsolete and we live in a
> fully CIDR world.
> Except that is, for the 'Class D' and 'Class E' (Multicast and
> Experimental) ranges which still exist. It's also why the loopback
> interface is given a /8 netmask -- 127.0.0.1 is a Class A address
> by this scheme.
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