4.2 Vax / IBM PC network with MIT PC/IP

[Brad Yearwood]

[choke your line-eater forever, feed it the 8086 architecture]

We are bringing up an internal Ethernet between our Vax 750 running
4.2 and some IBM PC/XT/AT's with the MIT PC/IP software.

In trying to get TFTP to run, I discovered an apparent bug in the
Berkeley UDP implementation.  The length field in the virtual
packet header that is used as checksum salt was not swapped from
Vax byte order to network order, which of course destroys 16-bit
checksum integrity.  A simple and obvious 2 line change to
udp_usrreq.c fixes this.

Also, the PC/IP package is much more convenient to operate in
an environment that includes a name server.  We wrote a simple
one.  In the process of bringing it up, we found that the "name"
entry in /etc/services was specified as 42/tcp rather than the
42/udp that it needs to be.  The name server, using UDP, requires
the previously mentioned kernel fix.

Server TFTP on the PC and user TFTP on the Vax appear not to
work for transfers from the Vax to the PC.  This holds both for
the standalone TFTP and for the one built into the PC user Telnet.
I think that the problem is in the Vax user TFTP, but haven't yet
had time to look.

Screen scrolling in PC Telnet is broken for many non-IBM display
controllers, and for the IBM Enhanced Graphics Adapter.  It appears
to be related to differing lengths of display memory on the various
cards, as the screen will fill with garbage or vertical stripes,
then revert to a readable state after some number of additional
scroll-ups.  (Hitting the F10 key twice in succession restores the
screen to a still-damaged, but more readable state.)

It would be good to hear from anyone with additional experience
with 4.2 networking or PC/IP, and any observations or fixes you may have.
We will continue to look at the more annoying problems.  If anyone is
interested in the name server, the UDP fix, or things we might
find in the future, let me know.
  
Brad Yearwood
Kontron Electronics
(714) 660-0270

  {ucbvax!unisoft | scgvaxd | trwrb}!pertec!kontron!brad