I'm having a weird issue with my network setup. I have an unmanaged TP-Link TL-SG1024S switch, and some wired devices on it just can't communicate with each other, despite being on the same network. My network consists of a Comcast business cable modem/Wi-Fi router combo, with the following connections:
- Port 1 connects to a Cradlepoint LTE router, which is unused right now.
- Port 2 goes to the TP-Link switch, where all the wired devices are plugged in.
On the network, I have two Wi-Fi clients (A and B) and three wired clients (C, D, E). Here are my ping results:
- All clients access the router and the Internet just fine.
- Wi-Fi clients can ping each other, and they can also ping the wired clients.
- Wired clients can ping both Wi-Fi clients and the router, but they can't ping each other.
Interestingly, when I moved client C to a different port on the Comcast router, it functions like a Wi-Fi client again. I initially suspected that the switch might be defective, but I'm confused as to how the wired clients can reach the router and Wi-Fi clients while being unable to communicate with each other. I thought a corrupt CAM table would prevent access altogether. If there was a network loop or broadcast storm, wouldn't the router be affected as well?
Before I look into replacing it with a managed switch, I'm hoping to gain some insights. I even asked AI for advice about the possibility of a switching ASIC failure, but I'm not sure how reliable that information is. What do you think?
4 Answers
Are you sure VLANs aren't causing the problem? Just to be clear, have you tried some ARP tests to see if the devices are recognizing each other?
What kind of ARP tests do you suggest?
Could it be that some devices are only using IPv4 while others are on IPv6? You might want to sniff the interface to check if ARP requests are actually sending or receiving on the switch.
That's a good point! I hadn’t considered the version differences. I’ll look into that for sure.
Have you tried rebooting everything? Also, double-check that your default gateways, subnet masks, and IP addresses are configured correctly. Sometimes clients can end up on a 'public' network, which can make it harder for them to see each other.
I’ll reboot, but I’m worried if it’s the switch, it won't fix the issue long-term. All clients are on the same 10.1.10.0/24 subnet, so they should be able to talk to one another just fine without even hitting the router.
Exactly, being on the same switch with matching IPs and subnet should mean layer-2 communication works. Without VLANs, it seems like the switch is to blame unless there's something weird happening with configurations.
Before diving deeper into troubleshooting, make sure to test your LAN cables. Sometimes, cable issues can cause strange behavior, even if some communication seems to work. It's worth ruling out bad cables first.
But if all clients are getting an IP and can access the internet, wouldn't that suggest the cables aren't the problem? I wouldn't expect three clients to be able to reach the internet but fail to talk to each other due to cable issues. Plus, one client is running a web server, so that means TCP should be fine too.
True, but I've seen odd layer-1 issues before that weren't directly about packet loss. It’s still smart to check.
No VLANs here, just an unmanaged switch! The TP-Link TL-SG1024S doesn't support anything fancy like that.