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I have two Modem/Router (Modem/Router A and Modem/Router B) and both of them have internet access (but they get internet from different service providers).

And I have one router (Router C) in living room that I use it as access point and I connected that to Modem/Router A. I also connect DVR to one of Router C LAN ports.

Modem/Router B is just for me and nobody else should connect to internet by Modem/Router B.

When I am using Modem/Router B, I can not see DVR cameras, and When I connect Modem/Router B to Modem/Router A by their LAN ports, people who connected to Router C got connected to the internet by Modem/Router B (Their public IP is the same as Modem/Router B public IP address) that I don't want that!

How can I connect Modem/Router B to Modem/Router A without sharing the Internet of Modem/Router B?

Note that due to physical limitations, I cannot connect anything else to Router C!

This is diagram

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  • Specific terminology matters in this instance: Since the modem has LAN ports with/without a dedicated WAN port, it's a modem/router combo (modems & routers use different programming languages, with neither language being compatible with the other). With Router A and Router B connected via ethernet, have you tried going into the Web UI of Router A to determine how it's vLANs are configured, as Router A should use Router A's modem for WAN unless the ethernet cable is plugged into Router A's WAN port. Does Router A have a dedicated WAN port or is its assignment controlled via the WebUI?
    – JW0914
    Mar 10, 2022 at 20:44
  • @JW0914 Router A and Router B? you mean modem A and modem B? because I have one router not two!
    – Fatemeh Akbar
    Mar 10, 2022 at 21:28
  • Please refer to my initial comment's first sentence, as the correct terminology matters in this specific instance. You have a modem/router combo if your modem has LAN ports with/without a WAN port - it's the router portion of the combo that's being asked about. (Modems cannot communicate over ethernet, other than to provide internet access via a WAN port, as modems and routers do not use the same communication languages and cannot communicate with one another beyond internet access over a WAN port)
    – JW0914
    Mar 10, 2022 at 21:32
  • Ok, yes you are right, my bad, they are both routers. should I disable DHCP on one of them?
    – Fatemeh Akbar
    Mar 10, 2022 at 21:36
  • @JW0914 I edited the question, Thanks for your clarification.
    – Fatemeh Akbar
    Mar 10, 2022 at 21:39

1 Answer 1

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Turn off DHCP at router B and block every device but your own (e.g. via MAC access table or better via certificates, whatever options the router gives you). Configure your PC(s) manually to access the router (via static IP, default gateway and DNS server).

Then you can connect router A and B assuming you configured them correctly (correct IP addresses etc.)

Note: with the MAC filter, there is no guarantee people won't get on if they do MAC spoofing.

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  • I think neither router A nor router B don't have MAC filtering option.
    – Fatemeh Akbar
    Mar 11, 2022 at 10:29
  • @FatemehAkbar you don't need MAC filtering options, it was just an additional option, even if you would have it, it's not really secure anyway (and it can't be made more secure without additional hardware). But you will reach your goal, as long as the people use DHCP, they won't use "your router"
    – Albin
    Mar 12, 2022 at 10:08
  • @FatemehAkbar yeah, I doubt that there's a better solution than the "DHCP/static split hack" unless you can replace router B with something that can provide you three interfaces (not switch ports) so that you can have like two "WAN"s (from the its LAN's perspective): one being router A's LAN and one being the Internet via ISP 2. (Also that won't even work if you need broadcast across)
    – Tom Yan
    Mar 12, 2022 at 10:36
  • Ok, I turn off DHCP of router B and set an IP address for that, then connect router B to router A by their LAN ports, also I enabled MAC filtering on router B and put my PC MAC address in white list, and inside my PC setting, I enter the router B IP address as default gateway. everything is ok now. but I have one other question, In this scenario, When router B doesn't have internet, my PC(s) couldn't connect to internet, I want that If router B is down, every device that their gateway is router B, access to internet through router A
    – Fatemeh Akbar
    Mar 12, 2022 at 13:29
  • You can set up a second IP address (default gateway, DNS server, etc.) on the networkcard with a lower "priority" (which would be a metric higher in value). But this is actually a different problem. If it gives you trouble consider creating another question.
    – Albin
    Mar 12, 2022 at 17:58

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