I'm troubleshooting a frustrating network issue with KPN in the Netherlands. At various customer locations, I've noticed that when certain PCs connect to the network, it causes the entire internet connection to become unstable or unusable for all devices. This problem occurs whether the PCs are connected via Ethernet or Wi-Fi, and interestingly, these same PCs work perfectly fine with other ISPs. All signs point to a compatibility issue with the KPN modem or WAN behavior under load.
Here's what I've observed:
- When one particular PC connects, the internet access fails for everyone else shortly thereafter.
- The local LAN may remain functional, but WAN connectivity drops or becomes unreliable.
- Disconnecting that PC seems to restore the network after some time or a reboot.
I've already ruled out many potential client-side causes:
- I've performed clean Windows installs multiple times, tried different SSDs, and even used various PCs with no antivirus, VPNs, or virtualization.
- I've switched offload features, experimented with different network interface cards (NICs), and confirmed the issue exists both via Ethernet and Wi-Fi.
- The problem comes up at multiple customer locations, all using KPN; it also happens even with a router set up behind the KPN modem.
- KPN doesn't permit bridge mode and refuses to replace the modem, which adds to the challenge.
Given these findings, I suspect it might be a firmware issue or GSM instability on the KPN side, possibly triggered by the traffic patterns of specific clients. Has anyone else experienced this with KPN or other ISPs? Are there known modem firmware issues, escalation paths, or any effective workarounds aside from changing ISPs?
5 Answers
If possible, have you thought about replacing the KPN router with a different model? I know they restrict corporate connections, but sometimes using your own router can work wonders on residential setups.
Since you've mentioned there's no antivirus or security software on the PCs, could it be that these devices are somehow linked to a botnet and overwhelming the connection? It might be worth considering a complete OS reinstall if you've already swapped out hardware.
Just to clarify, you replaced everything in the computers except the motherboards, right? Have you tried running a different OS like Linux on those PCs to see if the issue persists?
Yep, I even used a brand new computer with the same hard drive and still faced the same problems. Other devices don’t seem to have issues, which adds to the mystery.
Have you checked to see if the problematic PCs have the same hostname? Sometimes having a duplicate entry can cause strange network behavior. Consider changing that and see if it alleviates the issue.
Good point! I need to check that out. It’s strange, though; one machine that had problems used to work fine for about a year and a half.
Have you checked the network traffic to see what's going on between the problematic device and the router? It might help to analyze traffic patterns when the issues arise, even if it's not a constant problem. Tools like Wireshark could be useful for this!
I haven't really looked into that yet. Do you have any recommendations for user-friendly software? The issue doesn't occur all the time; it seems to happen after about five minutes.
I did set up a new router behind the KPN modem in DMZ mode, but the issues persist. It's odd because even with just one PC connected, there are still problems. That same PC works fine on my home network.