Is it possible to block dhcp traffic using iptables?

Solution 1:

I believe this is more or less the setup you envision. A connects to WiFi, and gets a IP address. B is connected to A via ethernet, and have their own (private RFC1918) IPs.

You want B to reach devices on the WiFi.

Now, A uses DHCP to get an IP on the WiFi interface. But it doesn't forward DHCP to different interfaces, unless you run a DHCP proxy. Furthermore, WLAN clients generally can't represent more than one MAC address, so somehow you'd have to assign an extra IP to A - or make A represent B's traffic on the WiFi.

The easy way to do this is to make A NAT traffic that's coming from ethernet, and forward it to wifi. This is what your home router does, and will allow B to talk to devices (and internet) on WiFi. Devices on that network will believe the traffic is coming from A, as they can't see B at all.

For how to NAT, see for instance this question.

You should not attempt to clone addresses or any similar silly ideas. IP's are meant to be unique.