Hi. I have port 4 of my 2762ac set as the WAN 2 port. It connects to a cable modem via approx 50m of cable. The problem I'm having is that this link is only running at 100Mbps, not 1000Mbps. Upon booting the router, a 1000Mbps is established briefly, according to the LAN Port section of panel control. However a few seconds later this connection drops, and re-establishes at only 100Mbps. This happens when the physical type is set to Auto Negotiation, and also when manually set to 1000M Full Duplex.

I have verified continuity end to end with a basic LAN cable tester and have confirmed the wiring order is correct as per T-568B.

Can anyone suggest anything that might help? Is there a log anywhere that might detail why the 1000Mbps connection is failing, and it is reverting to 100Mbps?

Thanks in advance.

Instinct says dodgy cable, can you bring the devices closer together temporarily for testing with another cable. Does your cable run near any sources of interference.....electrical cables, large devices?

I'd agree... suspect the cable... all 8 pins need to be connected. Take the router nearer and use another cable to test...

I had the same idea shortly after posting. Yes it would seem that there is an issue with the cable, as I brought the modem over to the router and connected them with a short cable. The connection successfully stayed at 1000M.

It's clear of electrical cables and appliances from what I can see. It is also a single cable end to end, so there are no wall sockets etc to worry about. What I did realise though is that it is only a Cat5e cable, not Cat6 as I thought. But 5e should still support 1000Mbps at 50 metres shouldn't it?

I'll see if I can do anything with the cable, starting by re-crimping the ends. Does anyone have any other suggestions at all? I'm keen to try what I can before swapping out the whole thing, as doing so is going to be a bit of a pain.

I've confirmed that all 8 pins are connected with one of those LED testers. I suppose that doesn't confirm the reliability of the connections though.

If you know the cable works, for example because you get 1GB when connecting a PC to the routers LAN and you know the modem supports 1GB because you get that link rate when you connect a PC to it directly, then the likely cause would be a negotiation issue. Manually trying 1000M Full Duplex was a good idea. In some cases this can be a chipset interoperability issue between the chipset in the switch on the router and on the modem. I've come across it with ISP cable modems from time to time.

If it is a chipset interoperability issue then a fix can sometimes to put a simple switch in between the two devices because swapping the hardware won't help if they're running the same firmware and hardware.

james.f wrote: But 5e should still support 1000Mbps at 50 metres shouldn't it?

Cat5, 5e and 6 all have a maximum length of 100M. 50M is pretty long but it's within the standard so should be fine.

Do you have any other devices that you can swap in at either end, a network switch, laptop, etc. to see what speed they negotiate on your cable?