[solved] Mac OS X PPTP VPN connects, but not forward traffic goes through

Most hotel wifis are open, so to secure my connections I’ve set up myself a PPTP VPN using QNAS TS-453A box (btw. great machine, get one!) to tunnel all my traffic via encrypted connection.

Windows 10 and Android are connecting to the VPN and the traffic goes smoothly, but my Mac OS X El Captain caused me quite a bit of grief – it connected to the VPN without a problem, the internal connections were working great, but the forwarding traffic got stuck. Ping was working fine, but WWW did not. Some initial parts of first website were loading and then the connection got stuck.

Cause:

The issue was caused by MTU mismatch. It seems that NAT on VPN server adds some headers, which cause the packet to be to big and get rejected.

Solution:

Go to apple->system preferences->network-><your connection>->advanced->hardware and set MTU to Custom with packet size 1400 instead of default 1500. You may want to experiment to find maximum MTU value that works for you.

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