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I was wondering if someone can help me out. I've some networking knowledge but I seem to be having a problem connecting two routers together and using different subnets.

I've a home network router provide by my ISP Eircom (F3000 Sagemcom) and another router which is a TP Link AC1200. I want to setup a site to site VPN and this doesn't seem to be possible on the F3000 router. I want to use a different subnet for the TP-Link router to keep things clean from a DHCP perspective for the VPN as there is multiple devices on the 192.168.1.0/24 network. The VPN part isn't yet relevant to my question though because I can't even get internet connectivity on the second router with the different subnet.

I've setup a reserved address 192.168.1.240 on the F3000 and connected the second router (TP-Link) to this. I then setup the Internet address as:

  • IP: 192.168.1.240
  • Subnet: 255.255.255.0
  • GW: 192.168.1.254
  • DNS: 8.8.8.8

Then I've setup the LAN with:

  • IP:192.168.2.254
  • Subnet: 255.255.255.0
  • DHCP Pool: 192.168.2.100 to 192.168.2.200
  • GW: 192.168.2.254 (for DHCP)
  • I've also disable NAT on the TP-link router

However theres no connectivity between the routers so something seems to be wrong but I can't quite understand it. Can someone maybe tell me if I'm incorrect with my setup or is this possibly just down to the home router expecting an actual WAN connection. Really hoping someone can point me in the right direction because I'm a little confused why this wouldn't work :(

I've included a diagram too if that helps at all.

Home Network Diagram

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    Connect the WAN port of the TP-link to a LAN port on the main router. Give the WAN an address of 192.168.1.x, ensure DHCP is ON and set up the DHCP range to 192.168.2.x to .y and that should work.
    – anon
    Commented Apr 12, 2021 at 19:53
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    @John: OP specifically said "I want to use a different subnet" though.
    – grawity_u1686
    Commented Apr 12, 2021 at 19:53
  • There are two different subnets in my answer
    – anon
    Commented Apr 12, 2021 at 19:54
  • How did you test that there is "no connectivity between the routers"? To be sure, you would have to ping one router from the other router using the router. This excludes pinging one router with a device in the other routers subnet. For that to work youd have to setup two routes on both routers.
    – jvda
    Commented Apr 12, 2021 at 19:55
  • @John Thank you. This is currently how I have it setup though and no joy.
    – DCUpro
    Commented Apr 12, 2021 at 21:18

1 Answer 1

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The Eircom router doesn't know where to send replies back to the 192.168.2.0 network. Find the "Static routes" section and add one:

  • Destination: 192.168.2.0/24
  • Gateway: 192.168.1.240
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  • Thanks @user1686 for your comment. That makes absolute sense. Unfortunately it still hasn't helped my problem though because there seems to be an actual connectivity issue between the routers. The F3000 shows the port is up and packets are being transferred but the landing page doesn't show the TP-Link router or the IP (shows all connected devices). I can't ping the IP for the other routers interface either. Starting to wonder is this a hardware issue. However they all work fine on the same subnet and the router shows on the landing pages to of the F3000
    – DCUpro
    Commented Apr 12, 2021 at 21:34

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