Can you try FTP download to NUL, in BINARY mode?
What's the CPU?
Do you have a managed switch? What's the link speed and duplex mode?

Edit:

You're using the latest drivers, right?

83-0809-001
3Com Fast EtherLink ISA Parallel Tasking 10/100 Base-TX
Version 2.0
Copyright 1997 3Com Corporation. All rights reserved.

Thanks at first for your response.

Reg 1: download to NUL to my understanding requires Linux. Is this right? How to do this in dos/win95 env? AFAIK NUL in dos is a hidden system reserved directory

Reg 2: See my specs for system 1 in my signature. ISA at 16MHz. Should hopefully not be important for real busmaster ops

Reg 3: yes managed switch with OpenWRT. Pls let me check the handled-out speed pls. Good remark. Max speed supported by the 515 config tool is 100MB HD

Reg 4: pls let me check as well. I use the driver out of vogons driver library (515n and 515x.exe). I am not aware of any other versions available even after searching through the whole internet 😀 I know it’s indeed a 1997er version.

Marco wrote on Today, 20:16:

Reg 1: download to NUL to my understanding requires Linux. Is this right? How to do this in dos/win95 env? AFAIK NUL in dos is a hidden system reserved directory

Download to /dev/null requires Linux, or any other Unix-style system.
Download to NUL requires DOS, Windows, or OS/2.
For example:

ftp 192.168.100.200
bin
get SomeBigFile.zip nul

Reg 4: pls let me check as well. I use the driver out of vogons driver library (515n and 515x.exe). I am not aware of any other versions available even after searching through the whole internet 😀 I know it’s indeed a 1997er version.

I can only see this - https://vogonsdrivers.com/getfile.php?fileid= … &menustate=47,0 - which is the older version:

83-0809-000
3Com Fast EtherLink ISA Parallel Tasking 10/100 Base-TX
Version 1.0
Copyright 1996 3Com Corporation. All rights reserved.

I'm attaching the newer thing...

Fantastic. Let me check this over the weekend to come back here afterward. Much appreciated.