[ih] The netmask

[Michael Grant]

Before CIDR sub-netting there were fixed subnets: A, B, C, D, & E.  (and 
from memory D and E came later).  What was the rational for this being 
represented as an actual bit-mask which could have been represented as a 
number of bits like we do today?  I know that not many protocols send 
the mask over the wire, aside from perhaps routing protocols.  Did any 
early protocols use say just 5 or even just 2 bits to represent classes 
before things went to CIDR?  I never saw anything like ifconfig report 
"Class C", it was always represented as 255.255.255.0.

I realize it's more efficient from a computing point of view to deal 
with bit-masks.  But I'm curious, from a historic point of view, why it 
wasn't just a number of bits or even just a number representing the 
class (A, B, C)?  In the old days when every byte of memory was sacred, 
it seems like it would have been thought of as wasteful.