Strange ethernet behavior on new gateway

ApexRon: I counted five devices though there were only four ports. Is there another LAN device that is missing from your list like a LAN switch?

No other LAN device - I just unplugged one device (the failed IBM laptop) and temporarily plugged my fifth device (TV) in to see if it worked on that port.  (It did.)

ApexRon: You stated, "Have tried switching the ports around at the gateway; the problem moves with the port." Did you mean to say that the problem moves with the cable?

Right - should have said I tried switching the cables around at the gateway into different ports.  If I take the cable from failed device A and plug it into different physical ports, the connection still fails; if I take a cable from a working device and move that, it continues working.

ApexRon: Your internal wiring is Cat-5 correct?

Correct.  FWIW, when I put plugs on the wiring I used the "B" configuration.  Port 1 on the gateway blinks orange; Ports 3 and 4 blink green.  Asked the tech why; he said color difference represented A vs B, but not to worry, it didn't make any difference.  This was one reason I needed to use patch cable, to eliminate any  possible A vs B-ism.

I have been monitoring the gateway's LAN - Wired Interfaces page (the one you posted) for the past two days and seen some oddities.  I have kept the working Acer desktop in Port 1 most of the time; gateway always shows that port UP, but usually at only a 10Mbps level.  But when I run speed test on the Acer desktop, it says almost 50Mbps (I have Internet 45 service). Once the gateway showed Port 1 at 1Gbp!  I have kept the working Brother printer in Port 4 most of the time; gateway always shows Port 4 UP at 100Mbps.  I have kept the failed HP desktop on Port 2 most of the time; gateway always shows Port 2 DOWN.  I have kept the semi-failing IBM laptop in Port 3 most of the time; gateway continually fluctuates on this one - sometimes UP at 100Mbps, sometimes UP at 10Mbps, sometimes DOWN.

OK, I will try your advice and see what happens when I turn off auto-detect.  Thanks for your help. 

[posted response 3/12, but for some reason it isn't showing up here]

ApexRon:  Your assessment and advice was 100% correct.  First via patch cable, changed my two "problem port"  connections (2 going to HP desktop, 3 going to IBM laptop) to 10Mbps at both gateway and device ends.  Success on connecting to HP desktop.  IBM laptop still acting strangely; gateway says UP but steady green and slow blinking orange at laptop end; laptop says Unplugged; gives internet anyway, but many pages not displaying correctly.  (This is an old 2005 Thinkpad with XP and no Windows updates for a long time, rarely used on the internet, so I won't waste any more time trying to troubleshoot it.)

Then I upgraded the HP desktop connection to 100Mbps and tested that, success!

Unfortunately, when I went from patch cord to internal house cable, discovered issue with the cable to HP desktop.  Am running HP desktop on the other internal cable/port until I can fix that issue.

Thanks much for your help

I have the same router ethernet connection problem as DaveinNC.  New 5268ac ATT-U-Verse router.  Three-year-old HP Pavilion 500 desktop computer with Windows 10.  Realtek PCLE FE Family Controller.  Can connect wirelessly, but not through ethernet unless I change speed & duplex to 100mbps half-duplex.  Neither Auto Negotiation nor 100mbps full-duplex works....it just says "Network cable unplugged" and does not connect wired.  I read that half-duplex means information can only be transmitted one direction at a time, so speed could be potentially slower than full-duplex.  Does the fact that half-duplex is the only thing I can get to work mean that I am stuck with it?

No doubt you've already tried this, but after resetting the connection at each end, did you restart the HP Pavilion?

One of my two problem devices kept coming up with the "cable not plugged" message, but after reboot resumed normal operation.

I have a solution!  At least it worked for me.  I wrote earlier saying I had the same problem as DaveinNY.  I could connect wirelessly to my new ATT U-Verse router, but not wired (ethernet cable), unless I changed the Speed & Duplex from Auto Negotiation to 100mbps Half-Duplex).  I had been researching/googling/talking to AT&T for two weeks.  I decided to write to Realtek (the maker of my network adapter....Realtek PCIe FE Family Controller).  I got a response from a Realtek engineer the same day asking me to go to the advanced tab and disable the "Energy Efficient Ethernet".  I did, and it works now.  I was able to put the Speed & Duplex back to Auto Negotiation, and now the wired internet stays connected!

Thank you.  I had tried that.  I had tried pretty much everything.  I just posted to this forum that my problem is finally solved.  See my other post for the solution that worked for me!

I adjusted the speeds on the modem and the computer and it resolved the problem as well.

Thanks everybody for help

hkrgal, that's great information.  Checked the adapter on my 5 year old HP Pavilion (Realtek adapter name slightly different than yours) - found an enabled setting called "Green Ethernet."  Haven't tried resetting that yet, since ApexRon's solution has me running OK at 100Mbps/Full.

Just FWIW:  My other PC, a late-model Acer, connected OK from the get-go, with Auto-Negotiation.  The only difference I see between Auto-Negotation and fixed 100Mbps/Full:  With Auto-Negotiation working, the gateway says port operating at 1Gbps and the orange light is on.  I have Internet 45 service, so my speed check is the same regardless of A-N vs 100.  Noticed that when the Acer is sleeping, the gateway resets the port to 10Mbps until that PC wakes up.  (Saves resources for the other ports, maybe?)