[ih] The netmask

[John Day]

Because networks come in all sorts of sizes and 255 is pretty small and it is along way to 65535 and lots of networks were in that range and it didn’t eat as much address space and of course the next gap was even larger.

It also is a part of the move to make IP addresses be addresses, i.e., location-dependent and route-independent, and arresting router table growth.

Prior to CIDR IP addresses were just flat identifiers.

Take care,
John Day

> On Jan 7, 2025, at 08:47, Michael Grant via Internet-history <internet-history at elists.isoc.org> wrote:
> 
> 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.
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