[ih] The netmask

[Craig Partridge]

ARPANET IMPs had 24-bit addresses, which perfectly fit with a class A
address.  ARCNET and the V2LNI Ring (which I think borrowed from an early
ring network?) both had 8 bit LAN addresses.  I don't know what ALOHA used
but wouldn't be surprised if it was 8 bits too.

Craig


On Tue, Jan 7, 2025 at 6:47 AM 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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