[SOLVED] Tunnel issues with Ubuntu 14.04 and SSL

[mastermind]

Hi,

For some time I'm using a tunnel on Ubuntu 12.04 without any issues.
After installing Ubuntu 14.04 on a new PC I'm having issues with the tunnel.
I can setup the tunnel and when I go to ripe.net I see I'm connected using IPv6.
However, setting up an SSH session to my server causes a timeout during negotiation and also SMTP (STARTTLS on port 587) is giving timeouts.
The tunnel configuration I used is exactly the same as I'm was using in Ubuntu 12.04 (of course I changed the local IP).

When enabling the tunnel again on the 12.04 machine, I can connect without any issues.

Firewall on the server is turned off when I connect using IPv4 I'm having no issues.

The MTU on both the tunnels is 1480, so that seems to be fine.

Does anyone have an idea what might be causing this issue?

Edit: Although both machines have the same MTU, the MTU still seems to be the issue.
After changing the MTU to 1280 my SSL connections are working as expected.
(Any of the higher MTUs from the advanced tab of the tunnel configuration keeps giving issues)