2 Mar
2026
2 Mar
'26
6:46 p.m.
On 02/03/2026 18.42, Paul Koning wrote:
Believe it or not. But my Multinet links in RSX, are run through the
DDCMP point-to-point handler.
All I do is add/remove the Multinet 4 byte header (well, I also make use
of that header, obviously). The rest I never had to touch.
On Mar 2, 2026, at 11:44 AM, Johnny Billquist
<bqt(a)softjar.se>wrote;wrote:
Hm. The command "MNC SET CIR IP-0-5 MODE DDCMP" should have given a warning
that this has been deprecated. In essence, it does nothing.
All links are just multinet links, which is DDCMP, with a small headerto just get whole
packets when using TCP.
Johnny
Well, Multinet is not DDCMP, it isn't even in the same province. PyDECnet certainly
supports that, and when used over TCP should work ok in spite of its fundamental design
errors. DECnet packet sizes are controlled by the executor
parameters, in particular the segment buffer size you mentioned. Yes, Ethernet supports
bigger frames, but 576 was the conventional max size used with DECnet. Actually, DDCMP
also supports much bigger frames (up to 16k is the max the protocol can handle) but that
certainly isn't normally done, especially noton PDP-11s for obvious reasons...
The reason for the size error in the logs is because RSX expects a
Multinet header before the DDCMP packet, which encodes the packet
length. And I do a little bit of sanity checking on it, and that's why
you see the error. I suspect/expect that when you say DDCMP on pyDECnet,
it don't have the Multinet header, so then the first 4 bytes are
interpreted as the Multinet header by RSX, which is not what it actually is.
Johnny