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I recently switched from AT&T DSL to Comcast cable, and I have a leftover Motorola NVG510 modem/router from AT&T. I bought a new modem for Comcast, and I want to use the NVG510 as a router only (not a modem).

My question is very similar to this one, and I've tried the solution to that question and the linked yahoo.com question.

If I simply connect the modem to one of the LAN ports on the back of the NVG510 and open up a web browser I get a page served from the NVG510 telling me it can't establish a DSL connection.

How can I use the NVG510 as a router only?

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Do you still need to connect other devices to the Comcast modem? Or is the NVG510 the only device connected to it? –  Rik Oct 1 '13 at 13:22
    
What type is the "Comcast cable"? And on your pc (direct connected to it) do you get a private-ip (10.* or 192.*) or a public-ip? –  Rik Oct 1 '13 at 13:34
    
@Rik, the NVG510 is the only device connected to the Comcast modem. The modem gives me a public IP address. I'm not sure what you mean about the type of Comcast cable. It is XFINITY cable internet running over a coaxial cable. –  MattL Oct 2 '13 at 19:07

2 Answers 2

You want to use an old DSL ==> wireless&Ethernet router as an ethernet router.

Unfortunately, it only has a DSL/telephone WAN port, so that's not going to work. The part you can plug into the WAN you have is only on the LAN side. The WAN port on the old Router is not not physically or electrically compatible with the ethernet port of the new WAN, since it is an ADSL modem which connects to a voice-type telephone line, not an ethernet port.

You'll need a router with an ethernet WAN port, which can connect to your single-public-IP address as provided by your new cable modem, and act as a router (presumably doing NAT unless you have other routable public IP addresses to use) and provide wired and/or wireless connections to that new LAN.

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If his modem only gives only 1 public-ip, and does not act as a DHCP-server, he does need the DHCP-server from the NVG510. And i think the instructions mentioned only work if the modem assigns a private ip (like 10.*). –  Rik Oct 1 '13 at 13:33
    
I guess based on your explanation that I want the NVG510 to work as a router not an access point. I'll update my question to reflect that. –  MattL Oct 2 '13 at 19:09
    
Cleaned up my answer to reflect the new information, and removed the now irrelevant information about using the old device as an access point. –  Ecnerwal Oct 3 '13 at 2:58

Like Ecnerwal already said, this is not going to work. (with just the NVG510 alone)

The problem here is that you're getting a public ip from your modem. This means the modem itself does not act as a DHCP-server. The other method you linked to only works if there is another DHCP-server.

Normally the router/access-point (NVG510) would get an ip from the modem via its WAN-port after which you could use its internal DHCP-server to issue private ip ranges on the LAN-side.

But because this WAN-port is a DSL-port and does not work (correctly) as a normal WAN-port you can't use it. So you would need to connect the modem to a LAN-port and that port should get the public ip. But thats not possible because all the LAN-ports should get the same ip-range to be able to communicate with each other.

There are 3 possible solutions to this:

  • You could use a computer to directly connect to the modem and share the internet via a second network-adapter. You can connect your NVG510 to that because your computer acts as a DHCP-server. Downside is that your computer always needs to be on.
  • You could get your hands on a cheap broadband router which only acts as DHCP-server (no WiFi necessary because you could connect your NVG510 to it)
  • You could buy a less-cheaper broadband router which also has wireless capabilities.
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