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I have the following topology: enter image description here

I have a laptop with a WiFi NIC and a docking station with an Ethernet NIC. Both network connections are connected to the same LAN. What I want to do is to use the Ethernet port as much as possible, and, when I decouple the laptop from the docking station, I want it to switch to the wireless NIC. I want all this without my services being affected/going down => I must have the same layer 3 address running all time and the WiFi NIC must always be connected to the wireless network, although no bandwidth is used.

I have thought of a solution (I'm using Linux):

  1. Disable DHCP on wlan0 and eth0.
  2. Add these interfaces in a bridge.
  3. Activate a DHCP client on the bridge interface.
  4. Make sure the bridge interface has the mac address of wlan0 so it can communicate properly on a secure WiFi network as well.

Some restrictions and concerns:

  1. Both physical networks are connected to a switch on ports which are set as vlan access port type. And I do not have any control over that switch.
  2. I do not know the DHCP protocol by heart. Do I risk wlan0 interpreting the DHCP response instead of the br0 interface?
  3. How do I prioritize br0 to use eth0 when it is active and consider wlan0 in a sort of a logical down status, without braking the wlan0 wifi connectivity?
  • Further research of DHCP protocol suggests that concern number 2 should not be a problem. DHCP uses UDP. So if no other DHCP userspace client is blocked on a recv() on that UDP port, there should be no problem with this, as only the DHCP client specific to br0 can interpret it. – Catalin Vasile Dec 3 '16 at 19:22

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