The VPN classification

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VPN is short for virtual private network. it provides a logical connection between the disconnected two sites. VPN can provide a secure remote connection, and it's widely used in the network.

According to the OSI model, the VPN can be established at the datalink layer, or at the network layer, or even at a higher layer. There are several types of VPNs which are widely used, they can be divided based on the OSI layer.

    (1) Layer 2 tunneling protocol (data link layer): Includes Point-to-Point Tunneling Protocol (PPTP), Layer 2 Forwarding Protocol (L2F), Layer 2 Tunneling Protocol (L2TP), and Multi-Protocol Label Switching (MPLS). ), and so on. 

    (2) Layer 3 tunneling protocol (network layer): includes Generic Routing Encapsulation Protocol (GRE) and IP Security (IPSec), which are the two most popular Layer 3 VPNs.

    (3) Session layer tunneling protocol: Socks are in the session layer of the OSI model. The Secks4 protocol, which provides a firewall that does not require authentication for client-server programs based on TCP (not including UDP) such as TELNET, FTP, HTTP, WAIS, and GOPHER. A VPN tunnel without encryption authentication is established. The Socks5 protocol extends Socks4 to support IPv4, domain name resolution, and IPv6 as defined in the secure authentication scheme specified by the UDP and TCP frameworks, and in the address resolution scheme.

    (4) Application layer tunneling protocol: Secure Socket Layer (SSL) belongs to the application layer tunneling protocol. It is widely used in web browsers and web server programs. Provide peer-to-peer authentication and encryption of application data.

There is another way to divide the VPNs.


As we can see from the picture, in this way, the VPN contains the MPLS L2/L3 VPN, these vpns are used to establish the connection between the network devices, rather than the remote PC.

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