The connection between the Vigor and Astaro cannot work using pptp, since the Vigor can only use CHAP as authentification and the Astaro allows only MS-CHAP. This could eventually be fixed with some hacking in the /var/chroot-pptp/etc/ppp options file.
I didn't succed yet. But please be aware that this won't be supported by Astaro.
You could possibly use an IPSEC connection, but I was not successful yet either. The Vigor supports PSK only.