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CM500 No Internet on Ethernet

it_tek
Aspirant

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I just replaced an out of date Arris with the CM500.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

Model: CM500-1AZNAS|High Speed Cable Modem—DOCSIS 3.0
Message 1 of 4

Accepted Solutions
antinode
Guru

Re: CM500 No Internet on Ethernet

> 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

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Message 3 of 4

All Replies
plemans
Guru

Re: CM500 No Internet on Ethernet

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. 

Message 2 of 4
antinode
Guru

Re: CM500 No Internet on Ethernet

> 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

Message 3 of 4
it_tek
Aspirant

Re: CM500 No Internet on Ethernet

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

Message 4 of 4
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