I've a normal LAN, connected to Internet through a DSL router, with private local IPs

Now I would like to use a low-end router (like a commercial Zyxel) to split the LAN in two, connected each other, different LANs.

What I suppose I have to do is:

  • connect the WAN port of the low-end router to an ethernet port of a switch belonging the original LAN
  • connect the devices that I want to migrate to the new LAN to a switch connected to the low-end router (for instance the integrated switch)
  • be sure that on the original LAN there is a DHCP server active (for instance run by the DSL router)
  • configure the low-end router internet connection to use the DHCP protocol to connect to internet
  • configure the devices of the new LAN with IP addresses and the gateway address, i.e. local (from the new LAN point of view) IP of the low-end router, manually or eventually by a local DHCP server run by the new router

Now the steps for which I'm not sure:

  • In order to permit the traffic from the original LAN to the new LAN, should I configure in the DSL router of the original LAN a static route rule to redirect the traffic to the new LAN IPs through the IP assigned to the low-end router (this obviously implies that the DSL router always assign the same IP to the low-end router, by configuring the MAC<->IP table of the DHCP server)? Or is this done automatically by some ARP table of the switches?

  • Is it ok to configure also the devices in the new LAN with the same class of IP as the original ( Now they are two seperate LANs, so it would be perfectly ok to have two devices with the same IP... or not? Because with two devices with the same IP, even in different LAN, I may see some problems with the previous point...

  • If you want to permit traffic from the original LAN to the new LAN, why make two separate networks in the first place? – David Schwartz Jul 10 '16 at 3:20

I'll admit, you lost me with your question. This is actually very easy to do (I've done it many times).

If your Zyxel router's address is in the same subnet as your "DSL router"--change it (e.g. Then plug the WAN/Internet port of your Zyxel router into a LAN port on your "DSL router".

That's it.

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