Unable to connect or ping to certain clients (Windows) Able to connect to others fine

[techmantrey]

Environment is this:
Windows 10 clients (3)
Windows 11 clients (1)

All authorized, all firewall settings correct, no AV blocking anything.

Issue: One of the windows 10 clients cannot connect/ping the windows 11 clients, but another windows 10 client from a different WAN can connect and ping the windows 11 client just fine. So some clients cannot communicate with others, while other can connect to everyone.

TLDR Ver: Some clients can connect to every client, while two seem to be unable to connect to each other.

Do you have any suggestions on what I could try to fix? I was reading there is a possibility these clients cannot setup a direct connection & are using a relay service for the connection. In that case a managed route would need to be created for these clients to be able to directly connect, but I’m unsure of how to set that up honestly. If it’s even needed! Let me know (:

[dajhorn]

Are one or both of the affected nodes behind NAT?

What is the output of zerotier-cli peers on the affected nodes?

And can these two nodes make direct connections with any other protocol like RDP or SSH?

If a restrictive NAT is involved, then kind of problem is often resolved by enabling UPNP on one or both of the border gateways and/or creating an inward port forwarding for ZeroTier.