IP address classes vs CIDR (was Re: Reviving ARPAnet)

[Eric Smith]

On Thu, Jan 18, 2018 at 10:39 AM, Grant Taylor via cctalk <
cctalk at classiccmp.org> wrote:

> I was not aware that there was code that supported /only/ Class A (/8)
> addresses and /not/ Class B (/16) or Class C (/24) addresses.
>
> I /thought/ that everything was either classful (as in supports all three
> classes: A, B, and C) or classless (as in supports CIDR).
>

Years ago I added a configurable "bozo-arp" feature to the Telebit
NetBlazer router, which would respond to ARP requests for non-local
addresses and reply with the router's MAC address (on that interface),
specifically in order to make classful-only hosts work on a CIDR network.
Later someone paid me to write a NetBSD daemon ("anyipd") to do the same
thing, though for an entirely different reason. Recently I've needed that
functionality on Linux, as I have multiple old systems that only understand
classful, including the AT&T UnixPC (7300 or 3B1). I suppose I should
rewrite and open-source it.