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I have a situation where I need 2 LANs to use the same ISP Gateway and ISP IP, but the LANs cannot be able to interact with each other. I am guessing I need two DHCP servers at the same scope. I have already tried having a DCHP server under the other DHCP server scope (but with a static IP) and setting up the nested DHCP server to use the upper DHCP server as the gateway and I could access the internet, except any device on the nested DHCP could interact with the entire LAN.

Since I can't just hook up 2 DHCP's to the modem and share the same ISP IP and ISP Gateway, do I need to have a router setup up as a gateway (by this I mean just take create a LAN, will turn off any DHCP and statically assign IPs) that which will use the ISP IP and Gateway, then have 2 DHCP's connected to that router and point them at the router for the gateway to the outside internet? If I do this, will one device on a DHCP not be able to see interact with a device on the other DHCP? Also, if I do this will I be able to setup a virtual server 'chain' so I could remotely SSH into a device under one of the DHCP's?

Is there any way I could do this with an linux based router firmware with a single router rather than 3? I'd prefer to do it in wrt if at all possible, but I wonder if I could do this in IPFire?

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  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin ♦
    Commented Aug 12, 2017 at 3:39

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You can logically create virtual LANs (VLANs) with each having a unique subnet and default gateway. Each of these LANs default gateway can be the same physical device. Typically, a trunk interface (802.1q) plugs into an Ethernet switch that has both VLANs configured, along with the trunk interface that plugs into the default gateway device which will likely be running NAT/PAT.

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  • Okay, thanks for the VLAN tip. I knew it was something with subnets but I didn't actually know VLANs were a thing and able to provide different subnets. I think I've almost got it all set up on DD WRT router.
    – kjoh
    Commented Jul 11, 2015 at 3:13

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