Just 40 meters beside our IT server room, there is a clinic and there is an ethernet cable is going from IT room to this Clinic and it is connected to a small wifi router , there are 3 devices connected to this wifi for internet, since two weeks the wifi connected devices are showing there is no internet access, then I checked the internet line going to the wifi router by connecting that line directly to PC , "it is working fine", I thought it is a router problem then I changed the router then also the same problem("no internet"), then I connected this line to one small switch and devices are connected to this switch, then also no internet available. the only problem I can see, after I directly connecting the line to pc I can see in network properties "connection speed=10mbps" usually it is "100mbps".What is the problem?speed 10mbps(problem linespeed 100mbps(normal line
Not sure this is still active. I have faced this issue recently, The ISP connection to any PC works fine but not on any router. I have captured packets and noticed there is a vlan tag on the packets. Configured a sub interface with the same VLAN on router and it started working. Seems like the ISP port is configured as Access with tagged VLAN.
Which WiFi router are you using? Also, are you connecting the Ether cable to the WAN port or LAN port? If WAN Port then is the WAN light blinking? Kindly login into your router and check the routing, the default route should be towards your switch, and from the switch it should be towards the ISP router. If possible kindly attach some pics of wifi router and switch for better troubleshooting. I think your wifi router is not getting a WAN IP from the switch. Kindly attach the internet cable, to the tp-link non-manageable switch, and from there attach it to the router and check.
It could be that the cable length is operating near it's limits and accidentally works with the PC but not with the wifi router. You need to verify the interface status when the wifi router is connected. You also need to look if there are any interface errors.