PPTP encapsulates the user information contained in PPP packets and supports tunnel switching. Tunnel exchange can open and allocate new tunnels according to the user's authority and transmit PPP packets in the network. In addition, tunnel switching can also direct users to designated internal servers. PPTP helps enterprises implement access control on firewalls and internal servers. Tunnel terminals located in enterprise firewalls accept PPP packets containing user information, and then implement access control on packets from different sources.
L2TP protocol combines the advantages of PPTP protocol and L2F (Layer 2 Forwarding) protocol, supports multiple tunnels, and enables users to access the Internet and enterprise network at the same time.
IPSec is a standard protocol to enhance VPN security. IPSec includes user authentication, authentication and data integrity. The protocol standard is formulated by IETF, which provides a series of IP-level protocols for encryption and digital signature between two IP workstations. When the tunnel is opened and terminated, IPSec realizes the interoperability of devices from different vendors. In addition, because the security function of IPsec is loosely coupled with the key management system, the security mechanism of IPSec does not need to be modified when the key management system changes.
MPLS-based VPN is a new network-based VPN solution, which requires the WAN to support MPLS and provide VPN users with virtual connections by using MPLS label switching. The advantage of MPLS VPN is that the whole network has strong unified management ability. Because MPLS VPN is network-based, all VPN network configuration and VPN policy configuration are completed on the network side, which can greatly reduce the overhead of management and maintenance.
The draft IP VPN based on network formulated by ITU-T puts forward the technical requirements of IP VPN based on MPLS. The network of service provider adopts IP technology, and the backbone network adopts MPLS. For IP VPN services, they can only be provided on edge devices, while for backbone devices, IP VPN services are transparent and conducive to scalability.