Have you tried a different ethernet cable? It may be as simple as that.
I have used a package called 3D Tracerouter (free version is available) to map routes and see where slow connections/drops are but
- Diagnostic traffic is often low priority and maybe slowed anyway
- Some devices will be configured not to respond to such traces
- If the network is busy such traffic may simply be dropped.
The problem may lie outside VM control so switching ISP may not help.
If you are connecting directly and you have no protection on your PC that may have been compromised. It may be worth scanning for malware. Also someone may have spotted your PC is connected directly and is trying to gain access.
It really is worth getting a router/firewall between the modem and PC. Get a cable (ie no built in DSL modem) device. If you do switch then all you need is to add the modem externally so money is not wasted. The firewall on the router will stop nasties out there getting in so easily and many have a log to show if someone is trying to scan/access your systems. Adding the firewall may make them simply go away.