I have an offline router I'm using to connect a remote wireless device.  The router cannot be configured as an access point, or I would just use it to extend the range of my existing WLAN and use the device that way, and it cannot otherwise be put online because of the location.  Note that I'm not trying to get the device online, I just want to be able to access it from another computer.I can obviously put a laptop on the offline router's LAN and connect to the remote device that way, but this means the laptop is also offline, which is inconvenient.  What I'd like to do is get the laptop online via my separate WLAN (which is in range of the router), and then connect to the router via ethernet cable and access the remote device that way.I'm not a NetworkManager user, so my preferred answer here is a sequence of ip commands (but if for posterity you want to leave an NM based one, feel free).  I've been looking through the ip man pages but am not sure where to start.I can assign static IP's on the router, and its subnet, 192.168.2.0/24 does not conflict with the main WLAN.
Connect to offline network on second interface
networking;ip;route
This turned out to be pretty easy.Assigned 192.168.2.102 to the laptop's ethernet MAC on the offline router, and 192.168.2.101 to the remote device.Connected the laptop to the main WLAN normally via DHCP.Raised the ethernet interface (ip link set eth0 up) and gave it the appropriate address:ip addr add 192.168.2.102 dev eth0Added a route to the remote device:ip route add 192.168.2.101 via 192.168.2.102I can now access the internet normally, and the remote device on the offline subnet (as 192.168.2.101).