I have a 100 Mbit/s router and all devices until recently were connected to it, so I was only getting 100 Mbit/s connections which makes sense.

Now I've disconnected all my devices from the router, added a 1 Gbit/s switch, connected the router and switch, and connected all other devices to that switch. On the switch I have two computers with 1 Gbit/s adapters and two connections which are 100 Mbit/s, one goes to a second router which acts like a hot spot. Why am I getting a 100 Mbit/s connection between computers with 1 Gbit/s adapters?

Shouldn't the router now handle 1 Gbit/s between the two? Is it possible that the switch is detecting the 100 Mbit/s router connected to it and as such throttling the connection?


  • Router #1: Asus RT-N12+
  • Router #2: TP-Link TL-WR1043ND
  • Switch #1: Linksys SE2500
  • Both PCs: Intel Gigabit Ethernet Adapter

I've also checked all cables. They are Cat 5e.

To better explain my situation here is my setup:

Enter image description here

SOLUTION: The problem was in connectors where not all pins were pushed all the way in.

  • 1
    "Why and I getting 100mbit connection between computers with gigabit adapters?" What do you mean exactly? What precisely makes you think you're getting a 100Mbit connection? Are you looking at the link lights on the switch? – David Schwartz Mar 10 '17 at 20:14
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    First off windows says its 100mbit under adapter status, second, I'm getting constant transfer speed of 11.5MB/s which would indicate a 100mbit connect, no? I've hooked the two PCs directly over a cable and manually set their IP to test the transfer and it went above 50MB/s. – Eric Mar 10 '17 at 20:16
  • @heavyd I did mention all my cables are cat5e. – Eric Mar 10 '17 at 20:17
  • What do the status lights on the switch tell you? (linksys.com/us/support-article?articleNum=142856) – heavyd Mar 10 '17 at 20:18
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    @ErikKralj Are the cables (between the switches and the devices that should be running at gigabit speeds) homemade or professionally made? Are you 100% certain they are wired correctly for gigabit? How long are they? – David Schwartz Mar 10 '17 at 20:20

The problem is likely in your cables. 1000BASE-T (gigabit ethernet on UTP) requires all four pairs of wires in the cable be connected correctly. If they are not, auto-negotiation will cause the interface to step down to 100BASE-TX (fast ethernet on UTP).

If even one of the two cables connecting the two 1000BASE-T PCs is not correct, then the two PCs will only be able to communicate with each other at 100 Mbps.

  • 1
    It depends on the scheme you are using. Look for T568-A and T568-B. You should use the same scheme on each end. – Ron Maupin Mar 10 '17 at 20:21
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    Look here and follow the straight thru 568B wiring. – David Schwartz Mar 10 '17 at 20:21
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    It is entirely possible that you have one bad wire out of eight. There a many crap cables sold, and it is easy to mess up on do-it-yourself cabling (using solid-core cable with connectors designed for stranded cable, etc.) – Ron Maupin Mar 10 '17 at 20:29
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    When this topic comes up, I like to add that cheap cable pinout/continuity testers are useful up to a point, but can't tell whether you got the twisted pairs right. Note that pins 3 & 6 need to be in one twisted pair, and pins 4 & 5 need to be one twisted pair. If you've already visually inspected the terminations on both ends of all your cables to ensure they're all T568B, then a typical cheap RJ-45 pinout/continuity tester is a convenient way to test continuity of each pin. – Spiff Mar 10 '17 at 20:41
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    @RonMaupin So today I took another look at all connectors, they were wired correctly, however I noticed some of them were not pushed all the way, so I clipped all of them, redid them and now I'm getting gigabit speeds, thanks to everyone for pointing me in the right direction. – Eric Mar 11 '17 at 14:19

I had a similar problem. My issue was that the Cat 6 cable from the RJ45 wall socket to my PC was too close to some power supplies. As soon as I moved the power supplies away Windows negotiated 1 Gbit/s speeds with no issue.

I spent hours trying to "repair" my drivers and configuration thinking it was a software issue.

  • 1
    What? This makes no sense I'm pretty sure there was a wire from socket to pc that was slightly needed modification or spreading . Have you tested with cable tester? – Elie Mar 10 '17 at 23:49
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    @Elie I suppose it's possible, but it would practically require both the cable and PSU to be utter garbage. – Michael Hampton Mar 10 '17 at 23:58
  • @Elie @Michael Hampton The only thing I changed was moving the power supplies away. It baffled me at that point, but I did not own any cable testers to check anything with. The cable is maybe 30ft and looks cheap, but not total trash. I initially tried testing with my linux laptop sitting under my desk. ethtool eth0 reported that 1Gbit/s was not supported by the link partner. With the cable coiled next to the wall socket 1Gbit/s worked fine. At that point I guessed something was causing interference along the way and moved a laptop and trashy usb 3.0 hub power supply that were touching it. – Kevin Mar 11 '17 at 4:26

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