DHCP relay through different subnets

dhcpdhcp-serversubnetzyxel

A TP-Link W8980 acts as a DHCP server on 192.168.0.0/24 subnet. This is also the only wifi access point.

A Zyxel USG 50 is connected to it through its 2 WAN ports and has static addresses 192.168.0.253 and 192.168.0.254

The Zyxel also acts as a DHCP server on 192.168.1.0/24 for the devices connected through its 4 LAN ports.

Is there any way to make the Zyxel the only DHCP server and create a unique 192.168.1.0/24 subnet, also for the devices connected to the TP-Link via wire or wifi?

I already tried to bridge WAN1 and LAN on the Zyxel and this way I can make the TP-Link to act as the only DHCP server, but this is not exactly what I want (and, furthermore, I lose the possibility of doing traffic balance on the 2 WAN ports of the Zyxel)

EDIT: I've made this simple image to better explain the situation. The desired result is that all the devices (wired or wifi) are on the same subnet

Desired result

Best Answer

The typical configuration for a single DHCP serving multiple subnets is to setup the subnets as routed (usually they are VLANS) and activate DHCP-Relay (helper-address or what else) on the device(es) working as routers.

If guess that the 192.168.1.0/24 network is behind NAT and not routed. Moreover I suppose that your network devices are "unmanaged" and don't support any of the needed features.

I think you cannot do that using your network equipment.

Maybe the guys at SuperUser, who deal with consumer level devices, could give you some tip.

EDIT:

Trying to guess, since I don't have any hands-on experience on your equipment:

  • disable NAT on the Zyxel (or connect the Tp-Link on a Zyxel LAN port)
  • setup two VLANS and assign the ports on both devices (Zyxel and TPLink)
  • Assign Ip Addresses to the VLANS on the Zyxel; check if you need to enable routing and/or setup specific policies
  • set up a Default Route on the Zyxel (something as 0.0.0.0/0 using the TP-Link as next hop)
  • you should not have to add any static route for the two VLANS on the Zyxel since both are "connected"
  • depending on your configuration, you will have to add some route to the TP-Link, informing it that the 192.168.1.0/24 network is behind 192.168.0.XXX (ip address assigned to the 192.168.0.0/24 VLAN)
  • setup DHCP for the two networks on the Zyxel
  • disable the DHCP Server on the TP-Link
  • configure the DHCP relay on the TP-Link (--> 192.168.0.XXX, see above)
  • cross your fingers

I would move the Zyxel at the border of your network, using it as Internet Gateway (instead of the TP-Link) and use the TP-Link as a bare access point. Different configuration: it would be cleaner.

Related Topic