I use a USB wifi stick on a PC with win 7 and it gets the IP address from the router, however the my RJ45 interface assigns itself a linked local address. When I assign an IP address from the same range as the wifi NIC gets I can access the web login page of the router but the further network are still unreachable. The behaviour persists after removing and re-adding the RJ45 rtl interface. The behaviour does not depend on the router, I have tried with two different vendors.
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show us some numbers. what interface is getting what dhcp address? What numbers are you assigning to what interfaces?– LarrycCommented Jan 26, 2020 at 13:01
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You should replace the used Ethernet cable and check if it changes something.– RobertCommented Jan 26, 2020 at 13:23
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I can open the web interface of the router when I assign an IP address from the same sub net manually, thus it is not cable, isn't it? superuser.com/users/62676/robert– Edik MkoyanCommented Jan 26, 2020 at 13:46
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The wifi interface gets a valid IP address that allows the machine to connect to the internet. How ever the rj45 interface does not get an IP address, but thee cable seems to be ok, see my previous comment.– Edik MkoyanCommented Jan 26, 2020 at 13:48
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@Robert you was right, please post an answer. It was the cable, but I still can't understand the root cause.– Edik MkoyanCommented Jan 27, 2020 at 12:43
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1 Answer
A non- or partially working Ethernet connection usually means that packets are getting lost between the sender and the receiver.
As you already have exchanged the router the remaining components that can be faulty are the Ethernet device in the PC or the used Ethernet cable.
A broken Ethernet cable can make a communication harder or even impossible. In your case I would assume that the DHCP message are getting lost because of disturbances in the cable.
The connection seems to work if you assign a static IP address because the used TCP protocol add another layer of error handling - lost packets are getting resent again and again, hence the chance of getting a "working" connection over a partially faulty cable is present. However the speed will be drastically reduced.
Therefore in case of indifferent network problems you should try to replace the Ethernet cable first. Ethernet cables can be damaged easily be mechanical pressure (e.g. by a office wheel chair) or by bending them.
