The network drops when the server is connected to the switch. How to make a diagnosis?

Question

linux

Good day. A couple of days ago this problem started.
We have a server on which PROXMOX is running, virtual machines are respectively launched on it.
This server is connected to a router (openwrt) that acts as a gateway.
Further, the router is connected to the switch, the switch gives the network to the office machines.
Such a problem began, pings to the external Internet from client machines began to be lost.
By the method of elimination, I found that when the interface on the server is disabled, pings are no longer lost.
How and why pings began to be lost is not clear.
Thanks in advance for help.

Answer 1

The network adapter on the server is not working, it happens.
Try to replace it and test it.

Answer 2

1. Check the interfaces on the server. Especially virtual ones, maybe they screwed up something and made a loop.
2. Check that the ip addresses do not match the existing ones.
Turn off all virtual machines, and turn on one at a time, monitor the state of the network.

Answer 3

The loop? =)