Philip Zimmerman found a little (6"x1"x3.25") Cabletron EA419 SCSI to
ethernet box, and I found documentation on how to speak to it.

After cajoling NetBSD to deal with it on the bus (it returns extra
data on INQUIRY) and adding the uk (Unknown SCSI) driver to the pc532
conf.c and files.pc532 file I was able to speak to it.  I then added
the tun (tunnel interface) driver to my kernel and wrote a bad program
to shuttle data between them (hardwired addresses, no ARP), and was
able to ping;

  home# ping -s pc532 1200 10
  PING pc532: 1200 data bytes
  1208 bytes from pc532 (192.9.200.4): icmp_seq=0. time=23. ms
  1208 bytes from pc532 (192.9.200.4): icmp_seq=1. time=23. ms
  1208 bytes from pc532 (192.9.200.4): icmp_seq=2. time=33. ms
  1208 bytes from pc532 (192.9.200.4): icmp_seq=3. time=26. ms
  1208 bytes from pc532 (192.9.200.4): icmp_seq=4. time=26. ms
  1208 bytes from pc532 (192.9.200.4): icmp_seq=5. time=34. ms
  1208 bytes from pc532 (192.9.200.4): icmp_seq=6. time=26. ms
  1208 bytes from pc532 (192.9.200.4): icmp_seq=7. time=25. ms
  1208 bytes from pc532 (192.9.200.4): icmp_seq=8. time=34. ms
  1208 bytes from pc532 (192.9.200.4): icmp_seq=9. time=29. ms

  ----pc532 PING Statistics----
  10 packets transmitted, 10 packets received, 0% packet loss
  round-trip (ms)  min/avg/max = 23/27/34

And a tcpdump of the same;
  02:12:38.372873 home ctron ip 1242: Ultimate.COM > pc532: icmp: echo request
  02:12:38.397289 ctron home ip 1242: pc532 > Ultimate.COM: icmp: echo reply
  02:12:39.381958 home ctron ip 1242: Ultimate.COM > pc532: icmp: echo request
  02:12:39.407385 ctron home ip 1242: pc532 > Ultimate.COM: icmp: echo reply
  02:12:40.392127 home ctron ip 1242: Ultimate.COM > pc532: icmp: echo request
  02:12:40.417588 ctron home ip 1242: pc532 > Ultimate.COM: icmp: echo reply

(1242*2)/.027 looks like around 900Kbps to me, which isn't stellar for
ethernet, but it's a lot faster than serial lines!

I'm having trouble setting protocol filters, so I'm running it in
promiscuous mode, and I can't establish FTP or TELNET connections for
reasons unknown, but it's a start.  The device only transfers packets
when polled, which is a bummer, and I've seen some disk timeouts when
I've ping'ed with really big packets.

The cabletron doc file I found mentions compatibility with "Kinetics",
which made a box called the Ether SC (looked like a FastPath except
the front pannel was green, not purple), so it's possible other Mac
ether products speak a similar protocol. I should pester some Mac
folks I know from a previous lifetime...

-phil