ZyXEL Communications P-334W - Manual (Page 234)

Prestige 334W User’s Guide
16-24 VPN Screens
Table 16-8 VPN IKE: Advanced
LABEL DESCRIPTION
SA Life Time
Define the length of time before an IKE SA automatically renegotiates in this
field. It may range from 60 to 3,000,000 seconds (almost 35 days). A short SA
Life Time increases security by forcing the two VPN gateways to update the
encryption and authentication keys. However, every time the VPN tunnel
renegotiates, all users accessing remote resources are temporarily
disconnected.
Key Group
You must choose a key group for phase 1 IKE setup. DH1 (default) refers to
Diffie-Hellman Group 1 a 768 bit random number. DH2 refers to Diffie-Hellman
Group 2 a 1024 bit (1Kb) random number.
Pre-Shared Key
Type your pre-shared key in this field. A pre-shared key identifies a
communicating party during a phase 1 IKE negotiation. It is called "pre-shared"
because you have to share it with another party before you can communicate
with them over a secure connection.
IKE Phase 2
A phase 2 exchange uses the IKE SA established in phase 1 to negotiate the SA
for IPSec.
Encapsulation Mode
Select Tunnel mode or Transport mode from the drop down list-box. The
Prestige's encapsulation mode should be identical to the secure remote
gateway.
IPSec Protocol
Select ESP or AH from the drop-down list box. The Prestige's IPSec Protocol
should be identical to the secure remote gateway. The ESP (Encapsulation
Security Payload) protocol (RFC 2406) provides encryption as well as the
authentication offered by AH. If you select ESP here, you must select options
from the Encryption Algorithm and Authentication Algorithm fields (described
below). The AH protocol (Authentication Header Protocol) (RFC 2402) was
designed for integrity, authentication, sequence integrity (replay resistance), and
non-repudiation but not for confidentiality, for which the ESP was designed. If
you select AH here, you must select options from the Authentication Algorithm
field.
Encryption Algorithm
The encryption algorithm for the Prestige and the secure remote gateway should
be identical. When DES is used for data communications, both sender and
receiver must know the same secret key, which can be used to encrypt and
decrypt the message. The DES encryption algorithm uses a 56-bit key. Triple
DES (3DES) is a variation on DES that uses a 168-bit key. As a result, 3DES is
more secure than DES. It also requires more processing power, resulting in
increased latency and decreased throughput.