Weird issue with cable modem, speed, and connection

  1. Posts : 32
    Windows 10 Home x64

    Weird issue with cable modem, speed, and connection

    I have an Arris cable modem from Spectrum. It has 4 ethernet out ports. For many months i've been running two ethernet cables out from it, 1 directly to my PC 3 feet away, and one to the router for the rest of the house.
    reason: if i go to the router, then out from that to my PC, i get about 65 Mbps. If I ran direct from the modem to my PC, I always speedtest at my full 120 Mbps. I gave up trying to figure out why my router was only yielding roughly half speed, and since a direct ethernet from modem worked, i left it at that.
    This morning upon turning on the PC, i had no internet on my PC. I checked, and the rest of the house is fine. Now, no matter what, I can't get internet to the PC on the direct line from the modem. If I run a line from the router to the PC, it works, but still at ~50% speed
    I have tried:

    • all network reset commands (netsh winsock reset, etc)
    • rebooting PC
    • rebooting modem (twice)
    • windows updates, incl drivers
    • running network troubleshooter
    • running ONLY direct line from modem to PC (pulled line from modem going to router)
    • switched ethernet wires
    • using 2nd ethernet in port on PC

    by the way, months back, in trying to solve the 50% speed problem, I went out and bought a new router with all the latest standards, and to my amazement, still got 50% speed. So yeah, I have no idea what's going on.
      My Computer

  2. hsehestedt's Avatar
    Posts : 989
    Windows 10 Pro, 1909

    If the cablemodem has 4 ports on it, that indicates that it also is acting as a router, so in effect, you have 2 routers.

    If both of these routers are acting as DHCP servers and assigning addresses to your PCs, you might want to check the settings to make sure taht they are not trying to hand out duplicate addresses.

    On the PC that was not working when connected to the cablemodem, make sure that you are connected to the cablemodem, then try to perform the following commands from a command prompt:

    ipconfig /release
    ipconfig /renew
    ipconfig /all

    After that last command, make sure you are seeing an IP address assigned from the cablemodem as well as a DNS server address and a default gateway.
      My Computers

  3. Samuria's Avatar
    Posts : 4,964
    windows 10

    Does the router have gigabyte ports if it only has 100 meg ports you can't get full speed
      My Computer

  4. NavyLCDR's Avatar
    Posts : 13,219
    Windows 10 Pro

    Samuria said:
    Does the router have gigabyte ports if it only has 100 meg ports you can't get full speed
    And, in addition, you need higher quality Ethernet cables to get Gigabit (1000Mbps) Ethernet than you do to get just Fast (100Mbps) Ethernet. Both cables from Router to Modem and from Router to PC would need to be the higher quality, CAT 5e or CAT 6 cable.

    In order to get full speed out of the router, the cable modem should be placed into bridged mode which effectively disables the router portion in the cable modem and passes all internet traffic directly to the router without any type of NAT firewall filtering. That would likely be the source of your speed drop through the router.
      My Computer

  5. bro67's Avatar
    Posts : 8,169
    Mac OS Catalina

    Install iPerf on that and another computer on the network, make one the server and other client the run a test from the client. You can also test with that computer and a public iPerf server after running the Internal test.
      My Computers

  6. Posts : 32
    Windows 10 Home x64
    Thread Starter

    Thanks for all the attempted help. Nothing worked. I finally got through to Spectrum and they believe the modem is faulty. I'll be switching it out tomorrow.
      My Computer

  7. bro67's Avatar
    Posts : 8,169
    Mac OS Catalina

    What are your power levels on the modem? On my xb6 for Comcast, I have to go to See this for proper signal levels. What should my Signal Levels be? Comcast High Speed Internet FAQ | DSLReports, ISP Information
      My Computers


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