I’m converting a campervan currently, and I’m going to have a Raspberry Pi (potentially among other devices) running inside the van at all times. Most of the time they will be connected via an exernal 4G antenna and I’ll have my own internet connection within the van, but when there is no signal in remote locations, the van will be LAN only.
I’m wondering if Tailscale can function offline, i.e. when there are two Tailscale devices on the same LAN, but no internet connection.
The benefit of this over using local IP address or custom local DNS records is that I can use the same address to reach the Pi whether I’m in the van offline, or away from the van and connecting over the internet.
If the client continues running, it will operate with the last network map it received even if unable to reach the control server. Currently active connections will continue working. If the client has not tried to reach a particular device on the same LAN recently, it may not know that device’s LAN address due to some battery life optimizations that were made on the control server a little while ago – that information is now typically distributed on-demand via DERP, so if you don’t have connectivity to the DERP relays then it won’t work. If the client restarts, it will not remember any of the details about other devices on the tailnet.
In conclusion, there are some circumstances where this would work fine but it will be a fairly brittle setup and there are situations where it will fail. I can’t give you a strong recommendation – it’s going to depend on your risk tolerance and ability to work around issues when it occasionally doesn’t work out.