Scenario 4 - Secure Site-To-Site Connections Using Ipsec Vpn; Application Scenario - ZyXEL Communications ZyWALL USG 20 User Manual

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– ZyWALL USG Support Notes
Scenario 4 — Secure site-to-site connections using IPSec VPN

4.1 Application Scenario

A virtual private network (VPN) provides secure communications between sites without the expense of leased site-to-site lines. A secure VPN is a combination
of tunneling, encryption, authentication, access control and auditing. It is used to transport traffic over the Internet or any insecure network that uses TCP/IP
for communication.
Internet Protocol Security (IPSec) offers standards-based VPN solutions that enable flexible scenarios for secure data communications across a public network
like the Internet. An IPSec VPN tunnel is usually established in two phases. Each phase establishes a security association (SA), a contract indicating what
security parameters the ZyWALL and the remote IPSec router will use. The first phase establishes an Internet Key Exchange (IKE) SA between the ZyWALL and
a remote IPSec router. The second phase uses the IKE SA to securely establish an IPSec SA through which the ZyWALL and remote IPSec router can send data
between computers on the local network and remote network.
The USG can provide secure site-to-site access between remote locations and corporate resources through the Internet. Using IPSec VPN, companies can
secure connections to branch offices, partners and headquarters as the illustration below.
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