Ike Phases - ZyXEL Communications SBG3500-N000 User Manual

Tunnel Mode
Tunnel mode encapsulates the entire IP packet to transmit it securely. A Tunnel mode is required
for gateway services to provide access to internal systems. Tunnel mode is fundamentally an IP
tunnel with authentication and encryption. This is the most common mode of operation. Tunnel
mode is required for gateway to gateway and host to gateway communications. Tunnel mode
communications have two sets of IP headers:
• Outside header: The outside IP header contains the destination IP address of the VPN gateway.
• Inside header: The inside IP header contains the destination IP address of the final system
behind the VPN gateway. The security protocol appears after the outer IP header and before the
inside IP header.

22.7.3 IKE Phases

There are two phases to every IKE (Internet Key Exchange) negotiation – phase 1 (Authentication)
and phase 2 (Key Exchange). A phase 1 exchange establishes an IKE SA and the second one uses
that SA to negotiate SAs for IPSec.
Figure 150 Two Phases to Set Up the IPSec SA
In phase 1 you must:
• Choose a negotiation mode.
• Authenticate the connection by entering a pre-shared key.
• Choose an encryption algorithm.
• Choose an authentication algorithm.
• Choose a Diffie-Hellman public-key cryptography key group (DH1 or DH2).
• Set the IKE SA lifetime. This field allows you to determine how long an IKE SA should stay up
before it times out. An IKE SA times out when the IKE SA lifetime period expires. If an IKE SA
times out when an IPSec SA is already established, the IPSec SA stays connected.
In phase 2 you must:
Chapter 22 IPSec VPN
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