Applicable for Windows 8.1. Extracted from the link http://technet.microsoft.com/en-us/library/jj900206.aspx:
"Windows RT devices come with an in-box VPN client implementation that is fully compatible with Microsoft Routing and Remote Access Server (RRAS) and supports both IPSec and SSL-based VPN access. The supported VPN protocols include PPTP, L2TP/IPsec, IKEv2 and SSTP."