diff --git a/content/posts/issues-with-openvpn-and-mikrotik/index.md b/content/posts/issues-with-openvpn-and-mikrotik/index.md new file mode 100644 index 0000000..410082e --- /dev/null +++ b/content/posts/issues-with-openvpn-and-mikrotik/index.md @@ -0,0 +1,45 @@ ++++ +title = "Issues With OpenVPN & MikroTik" +date = 2025-10-22 + +[taxonomies] +categories = ["Networking"] + +[extra] +author = "Emil Miler" ++++ + +I started having issues with my an existing OpenVPN tunnel after setting up a new MikroTik router in my home network. + +The symptoms were strange: I could resolve addresses through DNS, ping all hosts on the network, and access HTTP sites without issues. However, when I tried to SSH into any machine or access HTTPS services, the connection would time out. + + + +After checking the OpenVPN logs, I discovered the issue was this: + +``` +read UDPv4 [EMSGSIZE Path-MTU=1460]: Message too long (fd=3,code=90) +``` + +In short, the encrypted packets being sent were too large. + +## Fixing OpenVPN + +The preferred option is to change the MTU size in the OpenVPN configuration by adding the following: + +``` +tun-mtu 1440 +mssfix 1392 fixed +``` + +## Fixing MikroTik + +Other option, albeit not preferred, is to set maximum MTU size on `ether1` (WAN) to 1460 from the default of 1500. + +``` +/interface ethernet set ether1 mtu=1460 +``` + +Or in the GUI under `Interfaces > ether1 > MTU`. + +![winbox](winbox.png) diff --git a/content/posts/issues-with-openvpn-and-mikrotik/winbox.png b/content/posts/issues-with-openvpn-and-mikrotik/winbox.png new file mode 100644 index 0000000..4176407 Binary files /dev/null and b/content/posts/issues-with-openvpn-and-mikrotik/winbox.png differ