Are both computers on the same local subnet? How are they connected? In theory, provided that they are on the same local subnet and connected via a simple switch, their communication bypasses the router entirely. So they being unable to communicate with each other should be entirely due to their own software.
See if this helps:
I bet you're spot on! I have a managed switch between them, will do a bit of investigatory reconfiguring and see if that's the situation.
For testing purposes, you could temporarily connect both computers to the router's lan ports and see if ping works then. If yes then the issue is caused by the managed switch.
By default the Zerotier client only allows tunnel forwarding to RFC1918 "private" LAN addresses. Special configuration is necessary if you want to forward to a "public" IP or the whole Internet.
This should not be necessary if all you want to do is connect two LANs. Can you write out the IP subnets involved and make sure the routes are correct? Standard destination based routing requires all the various LANs and the tunnel itself to be non-overlapping subnets.
The only subnet I have at present is my default 192.168.1.0/ and the zerotier 172.28.28.0/.
These are the managed routes in ZT:
Edit: I removed 0.0.0.0/0 and 128.0.0.0/1 and still have connection to my phone on a different network, thank you!
That looks correct for a home router and a road warrior phone. The phone's Zerotier IP should be 172.28.28.2/24 or some number in that network other than 1.
Note that if the phone is connected to your home network, or a hotel, etc wifi using 192.168.1.0, there will be conflicting routes inside the phone (same subnet is both by zerotier and by local wifi). Test with the phone's wifi off so that it uses the LTE network. To prevent conflicts with public wifis, it is better to use an obscure range for the home LAN.
