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RT-AC68U slowing down wired connection

Discussion in 'ASUS AC Routers & Adapters' started by vespid, Oct 10, 2018.

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  1. vespid

    vespid New Around Here

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    Oct 10, 2018
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    Hi folks,

    This has probably been asked before, but I can't find an answer that works. I get 100Mbps at my modem and when I wire my PC directly into that modem, but when I connect through my RT-AC68U, the best I can get is 50Mbps or so. Nat acceleration is set to "auto" and I can't find any other settings that make a difference. About the same result when trying wireless. I've updated the firmware (which may be the problem, I suppose).

    What am I missing here?

    Thanks in advance for any help
     
  2. Grisu

    Grisu Very Senior Member

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    known bug with latest firmware, some reported same here ...
     
  3. ApexRon

    ApexRon Senior Member

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    While it certainly can be a firmware issue as indicated by Grisu, my experience has found it to be an auto-negotiation issue between your modem and the ASUS. This can be caused by the Ethernet cable, please try another, or just an incompatibility between the auto-negotiation of each device. Please refer to the ASUS to confirm that the connection to the modem is and remains at 1Gbps. Additionally, refer to the system log of the ASUS and see if an interface is posting "Link Down" and "Link Up".
     
    doczenith1 likes this.
  4. vespid

    vespid New Around Here

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    I swapped out the cable between the modem and router and it didn't make a difference. I don't see "link down" or "link up" in the logs anywhere, but I do see this. Once again, when I plug my desktop directly to the modem, I get the 100. Any other thoughts, or specifically, where to look among the many pages of settings on the router?

    upload_2018-11-4_11-16-43.png
     
  5. ApexRon

    ApexRon Senior Member

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    Congratulations, I believe you found the issue. That WAN connection should be 1Gbps regardless of your ISP contracted speed. Since your PC connects at 100Mbps too, I would replace the modem but this assumes that your PC Ethernet is 1Gbps capable.

    So why is the ASUS connection slower? The ASUS probably has a more current auto-negotiation code than the PC. The ASUS doesn’t like the modem’s auto-negotiations and continues to retry which in my experience will suck up ½ the bandwidth.
     
  6. vespid

    vespid New Around Here

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    This is my modem, supplied by my ISP. http://a.co/d/4ZVvdNZ Are you saying that I need to ask them for a different modem?
     
  7. ApexRon

    ApexRon Senior Member

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    Thanks for the link which states that it should support 1Gbps. So the question becomes:
    • Is it the Arris modem?
    • Is it your cable(s)?
    • Is it your PC’s Ethernet adapter?
    Note: Not including ASUS until you can get 1Gbps connection out of modem.

    Your choice on how to proceed.
     
  8. vespid

    vespid New Around Here

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    When I take the wire from my PC and switch it from the router to directly into the modem, I get this on a speedtest. To a newb like me, that implies that the modem and computer are ok, but I know it isn't that simple:
    upload_2018-11-4_16-26-31.png
     
  9. ApexRon

    ApexRon Senior Member

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    I suspect when the modem is directly connected to the PC, there are no auto-negotiation retries but the connection is only 100Mbps as you stated. Why your speed test is showing 120+Mbps I can’t explain because while it’s measuring ISP speed the actual methodology of how it accomplishes that is unknown to me.

    Until you validate that you’re getting 1Gbps on a modem connection you can’t consider the ASUS is at fault.
     
  10. dave14305

    dave14305 Regular Contributor

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    Please post the a screenshot of the Network section at the bottom of the Tools -> Sysinfo tab of your router (if you run Merlin Firmware). Interested to see what kind of negotiation is listed on the WAN port.

    Edit: Also, can you login to the modem at 192.168.100.1 to see how it sees the connection to the router?
     
    Last edited: Nov 4, 2018
  11. OzarkEdge

    OzarkEdge Very Senior Member

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    Given both support Gigabit Ethernet, the ASUS WAN port should connect to the modem port at 1 Gbps. You already know where to look in the router GUI to confirm this... it reports 100 Mbps, so the cable or ports are suspect.

    When you connect your PC to the modem, you can query the PC wired adapter status to confirm it's connected link rate... what is it? Given your speed test above of 100 Mbps, it may be 1 Gbps. So, maybe either the router WAN cable or port is suspect.

    Use the PC cable to connect the ASUS WAN to the modem. What's the link rate in the router GUI?

    OE
     
    Last edited: Nov 9, 2018