Yealink SIP-T2 SERIES Administrator's Manual page 719

Configuring Advanced Features
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VPN (Virtual Private Network) is a secured private network connection built on top of
public telecommunication infrastructure, such as the Internet. It has become more
prevalent due to benefits of scalability, reliability, convenience and security. VPN
provides remote offices or individual users with secure access to their organization's
network.
Types of VPN Access
There are two types of VPN access: remote-access VPN (connecting an individual
device to a network) and site-to-site VPN (connecting two networks together).
Remote-access VPN allows employees to access their company's intranet from home or
outside the office, and site-to-site VPN allows employees in geographically separated
offices to share one cohesive virtual network. VPN can be also classified by the
protocols used to tunnel the traffic. It provides security through tunneling protocols:
IPSec, SSL, L2TP and PPTP .
VPN Technology
IP phones support SSL VPN, which provides remote-access VPN capabilities through SSL.
OpenVPN is a full featured SSL VPN software solution that creates secure connections in
remote access facilities, designed to work with the TUN/TAP virtual network interface.
TUN and TAP are virtual network kernel devices. TAP simulates a link layer device and
provides a virtual point-to-point connection, while TUN simulates a network layer device
and provides a virtual network segment.
IP phones use OpenVPN to achieve VPN feature. To prevent disclosure of private
information, tunnel endpoints must authenticate each other before secure VPN tunnel is
established. After VPN feature is configured properly on the IP phone, the IP phone acts
as a VPN client and uses the certificates to authenticate the VPN server.
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