aa111 I have a user in another country who is connecting to my Synology NAS OpenVPN server from Windows 10 laptop (with the latest version of OpenVPN GUI client). Everything is working fine when she is connecting from her work office or some other locations. However, when she is connecting from her home (using the same laptop), OpenVPN GUI connects as expected, no errors displayed in logs, she can even browse shares and folders on the remote Synology NAS. But she can't transfer any data... Trying to open a file does nothing, trying to copy any file from the remote NAS to a local PC starts Windows file transfer dialog but it stays at 0% and doesn't progress. Her internet connection at home stable and over 100Mbps. As a workaround, I setup L2TP/IPsec VPN for her using built-in Windows VPN client and it works with no issues. Any ideas what could be causing this issue when using OpenVPN and how to fix it?
aa111 NAS LAN is on IP: 10.60.39.240 / 255.255.255.0 Laptop gets IP from home router: 192.168.188.10 / 255.255.255.0 Synology NAS OpenVPN server issues IPs in the range: 10.4.0.1 - 10.4.0.10
aa111 Pippin wrote Tried to disable the laptop firewall? Yes, tried disabling firewall, no difference. User's home ISP is running Dual Stack IPv4 / IPv6. Wondering if this could be the issue...
Pippin Sorry, no experience with Dual Stack (Lite) but from what I understand it can be a problem but i think only when server-side, not sure. In VPN Server-OpenVPN there is an IPv6 option if I'm not mistaken, tried also? Also check if connection is Public/Private/Work on laptop (or something like that).
aa111 All fixed! 🙂 After some experimenting found that the issue only occurs when OpenVPN runs over UDP. Over TCP everything works fine. After some more experimenting found that the issue was MTU size. Resolved by adding "mssfix 1420" to client's config.
