Raspberry Pi 3 wlan0 and eth0 on different subnetworks

Question

I'm wondering if it is possible for a Raspberry Pi 3, (which has an integrated Wi-Fi adapter). With the Pi running some network services (like a web server) can be connected to two different isolated networks at the same time.

For example, I would assign 192.168.1.10 to the wlan0 interface and 10.10.10.1 to the Ethernet iface. Assuming every interface is actually connected to its respective valid network, how would the device handle this situation? Would the web server be visible from both networks? Would I be able to reach hosts belonging both networks from inside the Pi?

Answer 1

Did you try it and failed ?

I have a Raspberry Pi3 connected to LAN #1 using ethernet cable ( 192.168.2.1 ), and Wifi to LAN #2(192.168.3.1 ), with no problem or specific configurations,

BUT there is no connection between 2 SubNets

Answer 2

Start by running:

sudo nano /etc/network/interfaces

Then edit the contents of the file so they look like this:

auto lo
iface lo inet loopback

allow-hotplug eth0
iface eth0 inet manual
    wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf

allow-hotplug wlan0
iface wlan0 inet manual
    wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf

iface NetworkOne inet dhcp
iface NetworkTwo inet dhcp

Exit the file with saving.

Then run:

sudo nano /etc/wpa_supplicant/wpa_supplicant.conf 

Edit the file so it looks like this:

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

network={
    ssid="NetworkOneSSID"
    psk="passwordOne"
    priority=1
    id_str="NetworkOne"
}

network={
    ssid="NetworkTwoSSID"
    psk="passwordTwo"
    priority=2
    id_str="NetworkTwo"
}

Again exit the file with saving. The priority line isn't necessary, it just means the Pi will connect to one network in preference over the other.

In theory the Pi should be visible on both networks, but it's not something I've tried yet but I am meaning to get round to it.

Answer 3

I know I'm a bit late but I'll leave here my experience in case someone still needs to know if it is possibile.

After doing some tests I figured out it is indeed possibile to connect the Pi3 to two different networks. I configured the dhcpcd.conf file to assign two different addresses (static or dynamic) to wlan0 and eth0 and the Pi could reach hosts from both network and was able to be reached from both networks.

What I didn't solve:

The only "problem" still present at the moment is that, connecting the Pi to two different networks may cause the Pi to stop being able to reach hosts outside those two networks (i.e. an internet host like a web server). Let me explain:

Let's say I connected the Pi to: WLan#1 throught WiFi and to Lan#1 throught Ethernet. If the external gateway (the one which is connected to WAN) is on WLan#1 I won't be able to reach external hosts from the Pi itself since the device automatically uses eth0 iface as the default one (so it where it redirects all requests to unknown hosts).

This results in the Pi not being able to reach an external network (which is not Wlan#1 or Lan#1, in the example above) unless you manually edit the routing table.

The Pi itself can't know which iface will have the access to a gateway so it is indeed perfectly normal that it uses the Ethernet access as the default one. The problem is that, as far as I know, there isn't any "simple" way to change the default iface. The only solution I found was to manually add a route entry through shell commands (which isn't ideal in my application scenario).

Additional notes:

Keep in mind that the Pi won't become a gateway between the two networks out of the box. If you weren't able to communicate between the two networks you still won't be able to do that, unless you configure some routing inside the Pi (which I didn't look into).