Can't seem to access server across Zerotier and Hamachi when behind OpenWrt

[jike212]

I have a remote server with Zerotier and Hamachi running an HTTP server and I have Zerotier and Hamachi on my PC.

My home router runs OpenWRT (18.06.1) and does not have Zerotier on it (I don't want to put Zerotier on the router)

When I'm on any other connection besides my home connection, I'm able to access the HTTP server on the remote server using the Zerotier IP address just fine. When I'm at home behind the OpenWRT router, I can ping the Zerotier server but I cannot access the HTTP server (it gets stuck on the "Connecting" phase).

What might be causing my inability to connect to a service behind a Zerotier or Hamachi IP address from behind OpenWRT?

[patrakov]

Looks like an MTU related issue. Not necessarily the fault of OpenWRT.

What I suspect is that the HTTP reply, wrapped in a Zerotier VPN packet, is too big for some part of the network between Zerotier/Hamachi and your router, and either the "Packet too big" message is filtered out, or fragments are (I encountered both cases in the wild with different software).

See https://github.com/zerotier/ZeroTierOne/issues/720

Note: the change must be done on both ends of the tunnel.

P.S. I am not a user of Zerotier or Hamachi.

[jike212]

That fixed it. My MTU was smaller than 1500 so I set it back to 1500 and the systems are accessible now, thanks!