Greetings!

  Mentioning pyDECnet might be a red herring, but that's what I'm using to connect to HECnet so I'm mentioning it.  I'm trying to connect to Mark Matlock's RSX11M.COM (Static IP:216.177.191.101) and we are getting some weird errors.

  My pyDECnet circuit line looks like this - modeled after Supratim's circuit config that he sent me last year.:

circuit DDCMP-30-1 DDCMP tcp:60001:rsx11m.com:7728 --t3=15 --cost=9

  On Mark's side he has an RSX11M host as the area router and the connection for me is set up thusly:

MNC SET CIR IP-0-5 MODE DDCMP
MNC SET CIR IP-0-5 TCP HOST 0.0.0.0:0 PORT 7728
NCP SET CIR IP-0-5 STA ON

  The connection isn't working.  Mark is seeing errors like this:

02:53:40  MLTNET - IP-0-5 Incoming packet size error (1541) from 
          76.213.76.105:51354. Abort.
02:53:42  MLTNET - IP-0-5 Incoming packet size error (1541) from 
          76.213.76.105:34404. Abort.
02:53:44  MLTNET - IP-0-5 Incoming packet size error (1541) from 
          76.213.76.105:34412. Abort.
  The A17RTR node has what look to be the normal settings.  the Segment buffer size is normal for DDCMP.

NCP>tell a17rtr show exe char


Node Volatile Characteristics as of  2-MAR-2026 09:35:20

Executor node = 17.1023 (A17RTR)

Identification           = THEMIS2 - A17RTR - DECnet/Python Area-17 Router at Saginaw, TX (DFW)
Management version       = V4.0.0
Software identification  = DECnet/Python V1.1.0
Incoming timer           = 30
Outgoing timer           = 30
NSP version              = V4.0.0
Maximum links            = 4095
Delay factor             = 32
Delay weight             = 3
Inactivity timer         = 300
Retransmit factor        = 5
Routing version          = V2.0.0
Type                     = area
Maximum area             = 63
Area maximum cost        = 128
Area maximum hops        = 16
Segment buffer size      = 576


Does anyone know what causes the packet size to be bigger than normal?  The ethernet interface on the pyDECnet host is set to 1500MTU as is my firewall/router. 

  Where else can I look?  I don't see anything in the pyDECnet documentation that talks about DDCMP packet size.  Where else can I look?

Regards,
  John H. Reinhardt