The provider removed the switch, now the Internet does not work in Linux, it works in Windows. What else can be configured?

Question

linux

Hello, this is what happened to me.
We are optically connected to the Internet. The connection scheme is such a linux router - network card - provider switch - media converter - optics
. I believe that the switch was supposed to perform some functions at the ethernet level (vlans or something else), but since we are the only clients, it was removed, The Internet was tested on a laptop.
Now I can easily and simply connect to their Internet on my work laptop, but I can’t do it in Linux.
because we have a stratified IP, then the minimum network setup always comes down to the banal:

ifconfig eth1 x.x.x.78 netmask 255.255.255.252
ip route add default via x.x.x.77 dev eth1

Guys, I tried different network cards, changed mac's and even different Linuxes. The result is one gateway is not pinged, the request interval has been exceeded. But, damn it, it works under Windows!
Tell me what else can be configured? Maybe this setting can be seen in Windows?

Answer 1

sudo tcpdump -nei eth1
Show me what's coming.
Wang that frames with a tag are flying in your direction.

Answer 2

Alternatively, if the copper is 100 Mbps, and you put it in the network for 1000, then it may not work.
There was such a jamb with coppers, so they used intermediate switches.