Three port USB Ethernet with micro B connection issues to Vodafone router Huawei HHG2500

I have a very intermittent connection between my brand new three-port USB Ethernet with micro B and Vodafone router Huawei HHG2500. I suspect it is something with auto-negotiation as the adapter works well on a Netgear GS208 switch. My good old Raspberry Pi 1 Model B onboard Ethernet adapter works fine on the very same Vodafone router. Wondering if there is a way to connect the two Pi’s back to back via USB or serial so that I could troubleshoot auto-negotiation issue somehow.

I have a couple of those. I only ever use the Ethernet briefly to setup Motion Eye OS, then switch to WIFI.
Have you tried setting up a static IP, as a test?

Thank you for your quick response! I use static DHCP and as a matter of fact, I see very intermittently some ping reply from the troublesome connection so I actually believe DHCP is successful. But actually instead of twiddling with serial connection I might just buy a USB WiFi adapter indeed.

I use these with my old Pi A+'s. I could have sworn Pimoroni also sold them but couldn’t find it on their site?

I’ve also used these with good results.

On my Pi Motion Eye OS setups, I set the static IP on the Pi itself, not as reserved on my router.
I just make sure to use an IP address outside of the range my router assigns.
I use and above as my router gives out the low ones etc.

thank you again for your exhaustive recommendation.

I have indeed tried to locate a USB WiFi here on Pimoroni but have to buy it from an alternative source:

It’s been my experience that the ones with the long rubber ducky antenna work better, range wise, than the small little dongle ones. They are a bit cumbersome though compared to what you linked too.

today my little usb wifi arrived and I could confirm that

pi@raspberrypi:~ $ sudo ethtool -s eth0 autoneg off

resolved the intermittency. I failed to make this change permanent and iperf3 measurements could not pass 50 Mbit/s so probably if works in half duplex.

I can’t pretend to begin to know what that means, lol. Anyway, rock on. =)