Hi Andreas, I'm also a customer of Kabeldeutschland Vodafone and can reach about 80 to 90 Mbit/s download speed. My router, a TP-Link WR1043ND, was not able to reach that speed until I updated openwrt to version 15.05, so routing performance was the bottleneck a long time. I'm connected to the PoP decgn01 with ping times about 25ms, I've set a MTU size of 1480 bytes. The routing performance of your router shouldn't be that bad if it's the bottleneck in your connection. Maybe also check the live tunnel status page for salient values.

The FAQ has a very nice article about this, causes for these kind of things can be many many things, see the FAQ for the details.

Andreas Wolf wrote: I think your should first try the speed form a PC to docsis 3 Modem/Router (bride-mode) with AICCU AYIYA , heartbeat is not supported by Draytek or try 6in4-static your Provider give a IPv4 for 180Days but only if your Router dont release the IPv4 on disconnect or reboot. but it very bad way to use a static 6in4 tunnel IP-change need manual edit on SIXXS User Home Tunnel endpoint and dont forgot about credits and ISK