>>12,13,25
記事を読めばちゃんと答えが書いてあります
ttp://vpnblog.info/security-issue-with-pptp-ipv6.html
> The security risk is caused by a combination of IPv6(Internet Protocol version 6) and PPTP-based VPN services.
> 1) Change PPTP-based VPN to L2TP, SSTP or OpenVPN. OpenVPN is more encrypted and more stable solution so it will be best choice.
Mon Nov 05 19:13:35 2012 WARNING: Since you are using --dev tun with a point-to-point topology, the second argument to --ifconfig must be an IP address. You are using something (255.255.255.0) that looks more like a netmask. (silence this warning with --ifconfig-nowarn)
Mon Nov 05 19:13:35 2012 There is a problem in your selection of --ifconfig endpoints [local=10.8.0.49, remote=255.255.255.0]. The local and remote VPN endpoints must exist within the same 255.255.255.252 subnet. This is a limitation of --dev tun when used with the TAP-WIN32 driver. Try 'openvpn --show-valid-subnets' option for more info.
Mon Nov 05 19:13:35 2012 Exiting