Can't connect from other network and LTE

[zeroduck]

I just installed ZeroTier hoping I can connect to Jellyfin from another location but it doesn’t seem to work.

Specifically, I installed Jellyfin using Docker on a virtual machine Ubuntu Server 20.04 on Proxmox VE 8.0.3. I installed ZeroTier on Ubuntu Server following this guide and same on IOS phone, everything works fine, I ping from ubuntu to my phone fine, I try to connect to jellyfin via Managed IP of my phone it works efficiently.

But the problem appeared when I added my brother’s IOS phone who is currently in another city to the ZeroTier network I just set up as mentioned above. Authentication (Auth) on ZeroTier Central has no problem, but when my brother connects to Jellyfin server, it fails to connect. I tried pinging from the Ubuntu server on my brother’s phone and it didn’t work. I realized my phone was connecting to the Jellyfin server because it was still on the same local network, so I tried turning off Wifi and turning on LTE on the phone and it immediately stopped connecting to the Jellyfin server. I try ping again on ubuntu server and it doesn’t work.

Then I tried to download Tailscale and it was miraculous that it worked perfectly, but when I tried to watch a movie, it couldn’t download (probably because tailscale’s connection was not good). So I still want to try ZeroTier. Can anyone help me find the cause and solution of my problem?

[mdr]

Check on your Ubuntu server if packet forwarding is enabled.

cat /proc/sys/net/ipv4/ip_forward

This command should give 1 if enabled and 0 if disabled.

Did you setup a Managed Route to your LAN via your Ubuntu server?

[zeroduck]

I just followed this video and it worked, now I can ping from my Ubuntu server at home to my phone and laptop at work. I tried to measure the performance and encountered a rather strange situation that in my laptop ping to ubuntu server average 172ms and zerotier is 141ms. But on my phone it’s reverse tailscale is 169ms and zerotier is 197ms. I tried iperf3 from ubuntu server to laptop, now only tailscale works and zerotier doesn’t work at all. So what do I need to do for Zerotier to run iperf?

UPDATE: I just tried iperf3 from laptop to Ubuntu server and it works, probably Windows or something causing iperf3 from Ubuntu server to Laptop not working. Impressive that with Zerotier I get 13.5 Mbits/sec both sending and receiving, but with Tailscale only 3.88Mbits/sec send and 3.71Mbits/sec receive.