What is a VPN?

The full name of the VPN is "virtual private network", the translation is "fictitious dedicated network". VPN is defined as a temporary, secure connection through a public network (usually the Internet), a secure, stable tunnel through a chaotic public network. VPN mainly uses tunneling technology, encryption and decryption technology, key management technology and user and equipment identity authentication technology.

The functions that a VPN can provide: firewall function, authentication, encryption, tunneling. A VPN can connect to the Internet through a specially encrypted communication protocol, establishing a proprietary communication line between two or more enterprise intranets located in different places, just like a dedicated line, like passing a safe tunnel to the destination without paying for the construction of the tunnel, But it doesn't really have to be the physical wiring of the cable.

The common virtual private network protocols are:

IPSEC:IPSEC (abbreviated IP Security) is the standard for secure communication of IP protocol, which mainly encrypts and authenticates IP protocol packets.

IPSec as a protocol family (that is, a series of interrelated protocols) consists of the following parts: (1) Protection of packet flow protocols; (2) key exchange protocols used to establish these secure packet flows. The former is divided into two parts:

Encrypted packet flow Encapsulating Security Payload (ESP) and less-used authentication headers (AH), the authentication header provides authentication to the packet stream and guarantees its message integrity, but does not provide confidentiality. So far, the IKE protocol is the only key exchange protocol that has been developed.

Pptp:point to Point tunneling Protocol--Point-to-Point Tunneling protocol

The Protocol of establishing the IP Virtual private network (VPN) tunnel on the Internet is to establish the communication mode of the Multi-Protocol secure virtual private network on the Internet.

L2f:layer 2 Forwarding--second-tier forwarding protocol

L2tp:layer 2 Tunneling Protocol--second-tier tunneling protocol

Gre:vpn third-Tier tunneling protocol

Openvpn:openvpn uses the OpenSSL library to encrypt data and control information: it uses OpenSSL encryption and validation capabilities, meaning it can use any OpenSSL-supported algorithm. It provides an optional packet HMAC feature to improve the security of the connection. In addition, OpenSSL's hardware acceleration can also improve its performance.

MPLS VPN Set tunneling technology and routing technology, absorbing the advantages of QoS guarantee of VPN based on virtual circuit, and overcome the shortcomings that they failed to solve. MPLS Network has excellent flexibility, scalability, users need only one line access to the MPLS network, you can achieve direct communication between any node, can achieve the user nodes between the star, the entire network and any other form of logical topology