L2TP/IPsec

L2TP is a network protocol that creates a tunnel between an L2TP client and an L2TP server and then encapsulates PPP frames to be sent over the tunnel. L2TP is defined in RFC 2661 for different types of media, such as Frame Relay, X.25, or IP. When using IP as the transport protocol, L2TP can be used as a VPN protocol over the Internet.

L2TP over IP uses UDP encapsulation for both tunnel creation and maintenance and data transmission. With L2TP, both the tunneled data and the control messages share a single UDP stream, which can simplify the passing of VPN data through corporate firewalls. L2TP traffic sent by the VPN client and server in Windows Server 2008 and Windows Vista use UDP port 1701 for both the source and destination UDP ...

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