One Modem Multiple Routers

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Priamo Gregory

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Aug 3, 2024, 5:28:12 PM8/3/24

to ecintuane

I know that most of you will think this question is a duplicate many times over, but I cannot seem to find help anywhere for my specific problem. I have a home neowork using a ClearAccess modem/router combo in bridge mode, with a tp-link router connected to a LAN port from the WAN port and acting as a router, all very usual.
Default gateway: 192.168.0.1

I set that all up when I got the router (the modem/router combo unit used to do everything). But then I found out that a computer can act as a router and I want to try this out. The modem/router combo has a 4 port switch in the back. Is it possible for me to connect another router (in this case an old pc) to the modem/router? I do not want the networks to see each other or interfere with each other.

Should not be a problem. You are actually making two separate home networks that will use the wan router for accessing internet. So each router will see the wan router (which has several ports). The routers have two interfaces each. The one facing wan router will be on wan router's internal subnet. So there will be a small subnet with three participants. Now the other sides of your internal routers may well have the addresses you mentioned and they will be separate, each of their subnets behind its own router. That is it really.

Your ISP probably won't help you do this, because they would need to at least give you two IP addresses at the same time. Furthermore, if you wanted to truly have them segregated, you would need to have the vLANs trunked, which the ISP is also not likely to do. Otherwise, the two uplinks would be on the same network.

I bought a Gigaware Splitter/Combiner. The modem has only 1 ethernet port. I thought I could use the splitter to branch off to each router, but it does not work, only one router is available at a time, or so it seems.

Typically the cable or DSL modem allows only one device to be connected (because it supplies only one IP address). You should instead connect one of the wireless/routers to the other: from the one that has is by the modem run the ethernet from one of its LAN ports to the WAN (internet) port of the second router.

The routers will connect to a port on the switch and then connect to the wan port on each of the router. Then each router will have its own dhcp and the devices I have will connect to each router on its own network.

In the Edge, you define a NAT/PAT (masquerade) rule for each of your LANs to the port 0 IP address. You also define a DHCP scope for each interface. If you want to isolate the LANs, add firewall rules that prohibit that traffic.

As far as I understand, that relates activation of layer one. Your switch is serving layer one and two, eventually even more. So when that link is activated by modem and switch, it may not prevent activation of any other ports of your switch. So your routers will reach activated links too.

So while what you read sounds nonsense, it may nevertheless be the case that your ISP has implemented other restrictions, e.g. by routing or filters. And it is the question if when he implements any additional restrictions, if these restrictions do comply with the terms and conditions of your service provider and with its contracts it have with you and if all these comply with public regulation. If he applies such further restrictions and neither his T&C nor his contracts specify such restrictions, you may complain to your ISP until he provides services complying to his T&C and his contracts. And these T&C and contracts provide also rules how he may adapt his T&C and contracts for already existing contracts. Usually, he may only change upon expiry and options for extra-ordinary contract resiliation are limited.

OK thanks, everyone. I have some thinking to do. I really needed the two routers working together and giving each its own DCHP because of certain reasons. I understand the wifi channels not overlap. Thank you for explaining the edge router.

I'm new here, so maybe someone can help me understand the purpose of ports 2,3,& 4 on the CM1200. I had hoped to use these ports to send a signal directly to my TV (using Apple TV) and a LAN switch so that I can have hard wire connections in several rooms. From what I'm reading, this Modem is not able to do this. So I'm not really sure why I bought this version of the modem since I probably should have just picked up the single port version.

Obviously I'm not a network guy, so maybe I made the wrong purchase. Is there a cable modem that supports DOCSIS 3.1 and has multiple ports I can use in the way I described above? Is the CM1200 not the right modem for my application?

The cm1200 confuses a lot of people and there isn't good education done on it from netgear or isp's. Half the problem is that there are ISP's that support multiple public ip addresses. in those cases you can hook multiple devices to it. But those ISP's are rare. the big 3 (comcast, cox, spectrum) don't support more than 1 public ip address unless you pay for it or have a business class line.

Ports 2,3, and 4 are for ISP assigned WAN IP addresses. So if your ISP supportings having more than on WAN IP address going to the modem, then these ports would be use for this. So you could have up to 4 external wifi routers connected to the one modem.

@stockylobster if the modem is in Gateway mode, you can connect routers to all fours ports if you wanted to, but, I wouldn't want to predict what IPV6 addresses you would end up with for each router and its connected devices.

If the modem is in Bridge mode, you can connect routers to all four ports. Two of those routers will end up with IPV4 and IPV6 addresses. The remaining two will only end up with IPV6 addresses. I don't know how to predict which router will get one or both, other than connecting two routers first so that those routers end up with both addresses, and then connecting the other two routers which should only receive an IPV6 address.

Keep in mind that with the modem in Bridge mode and two routers running, both routers are independent of each other unless you happen to configure a VPN between the two. Without that VPN inter-connect, each network would run independently from the other one. If you wanted to run one router with normal internet access and one router with VPN access only, this would be a way to do it.

Fwiw, with my 4582 running in Bridge mode, I run an Asus RT-86U and just connected an Asus RT-AC68U just to check this out once again. I typically do this for test purposes, run two routers at the same time. The 68U picked up its IVP4 address automatically. I have to check on the IPV6 configuration in the 68U, but don't time at the moment. I usually use IPV6 for test purposes only. I don't expect you to have any issues with either the IPV4 or IPV6 addresses.

If the second router doesn't pick up its addresses after its connected and booted, reboot the modem. Pull the power off of the modem, wait for 10 to 15 seconds and plug it back in. That should resolve the situation.

What is the recommended way to connect the multiple PPoE devices to the modem/router? The modem/router in question is a consumer grade Netcomm device. There is no intention or requirement to replace this.

Just a brief sanity check: Does your ISP provide you with two distinct WAN IP addresses, each to be established using PPoE across the same physical connection (your modem in bridge mode is now an L2 device)?