Chapter 16 VPN
P-661HNU-Fx User’s Guide
227
DH You must choose a key group for phase 1 setup. DH2 refers to Diffie-
Hellman Group 2, a 1024-bit random number. DH5 refers to Diffie-
Hellman Group5, a 1536-bit random number, and DH14 refers to
Diffie-Hellman Group 14, providing 2048 bits of key strength.
SA Life Time
(Seconds)
Define the length of time before an IPSec 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.
Phase 2
Encryption
Algorithm
Select 3DES, AES-128 or AES-256 from the drop-down list box.
When you use one of these encryption algorithms for data
communications, both the sending device and the receiving device
must use the same secret key, which can be used to encrypt and
decrypt the message or to generate and verify a message
authentication code. 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.
This implementation of AES uses a 128-bit key and a 256-bit key. AES
is faster than 3DES.
Authentication
Algorithm
Select MD5, SHA1, SHA2-256 or SHA2-512 from the drop-down list
box. MD5 (Message Digest 5) and SHA1 (Secure Hash Algorithm) and
SHA2 are hash algorithms used to authenticate packet data. The
SHA1 algorithm is generally considered stronger than MD5, but is
slower. Select MD5 for minimal security and SHA-1 for more security.
SHA2-256 or SHA2-512 are part of the SHA2 set of cryptographic
functions and they are considered even more secure than MD5 and
SHA1.
SA Life Time
(Seconds)
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.
Perfect Forward
Secrecy (PFS)
Perfect Forward Secrecy (PFS) is disabled (NONE) by default in phase
2 IPSec SA setup. This allows faster IPSec setup, but is not so secure.
Choose DH2, DH5 or DH14 from the drop-down list box to enable
PFS. DH2 refers to Diffie-Hellman Group 2, a 1024-bit random number.
DH5 refers to Diffie-Hellman Group5, a 1536-bit random number, and
DH14 refers to Diffie-Hellman Group 14, providing 2048 bits of key
strength.
Table 59 Security > VPN > Setup > Edit > Advanced Setup (continued)
LABEL DESCRIPTION
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