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it_tek's avatar
it_tek
Aspirant
Mar 20, 2021
Solved

CM500 No Internet on Ethernet

Hi,

I just replaced an out of date Arris with the CM500. Took awhile just to get it to connect, but we finally got it. I have a 5 port switch coming off the one ethernet cable. I have one laptop on that switch and a google wifi box. It took me a very long time to get the wifi going and up until I did the one laptop was ok. As soon as I got the wifi  goind and plugged it into the switch, the laptop now has no internet on the wire coming out of the switch. I decided to see if I plugged the wifi in first and then coming out of the wifi into the switch then the laptop pics up the wifi box name and gets connected. I plugged another laptop into the switch and it wouldnt connect. Is this normal? I have had modems before that i connected wifi routers to that also had hard ports working just fine. Please clue me in here. I dont mind returning something and buying a better box.

 

Regards,

Tom

  • > The modem only gets 1 public ip address. It assigns that to the router
    > which then sets up private ip addresses.

     

       Not really.  The modem does not get an external IP address from the
    ISP.  The (first?) gizmo which is connected to the modem would get that
    external IP address from the ISP.  The ISP grants that address to the
    gizmo (typically a NAT router), not to the modem.  The modem's only
    involvement is as a conduit.

     

    > If you put the switch before the router, it gets that public ip
    > address and not a private one.

     

       I wouldn't expect "a 5 port [unmanaged] switch" to get _any_ IP
    address, but only one device (at a time) can get the one external
    address from the ISP, and that's bad enough.

     

    > You need to go modem---->router--->switch

     

       True-ish.  Ethernet is bidirectional, so a more accurate
    representation would be: ISP <--> modem <--> NAT router <--> switch

3 Replies

  • You need to go modem---->router--->switch

    The modem only gets 1 public ip address. It assigns that to the router which then sets up private ip addresses. 

    If you put the switch before the router, it gets that public ip address and not a private one. 

    • antinode's avatar
      antinode
      Guru

      > The modem only gets 1 public ip address. It assigns that to the router
      > which then sets up private ip addresses.

       

         Not really.  The modem does not get an external IP address from the
      ISP.  The (first?) gizmo which is connected to the modem would get that
      external IP address from the ISP.  The ISP grants that address to the
      gizmo (typically a NAT router), not to the modem.  The modem's only
      involvement is as a conduit.

       

      > If you put the switch before the router, it gets that public ip
      > address and not a private one.

       

         I wouldn't expect "a 5 port [unmanaged] switch" to get _any_ IP
      address, but only one device (at a time) can get the one external
      address from the ISP, and that's bad enough.

       

      > You need to go modem---->router--->switch

       

         True-ish.  Ethernet is bidirectional, so a more accurate
      representation would be: ISP <--> modem <--> NAT router <--> switch

      • it_tek's avatar
        it_tek
        Aspirant

        Thanks guys. Makes perfect sense. I can live with it until I decide on something else more to my liking. I should have read more into it. Thanks to you both!

         

        Regards,

        Tom