Filter
Top Products
Chapter 21 IPSec
VSG1435-B101 Series User’s Guide
257
21.3.1.2 Manual Key Setup
Manual key management is useful if you have problems with Auto(IKE) key
management.
21.3.1.3 Security Parameter Index (SPI)
An SPI is used to distinguish different SAs terminating at the same destination and
using the same IPSec protocol. This data allows for the multiplexing of SAs to a
single gateway. The SPI (Security Parameter Index) along with a destination IP
address uniquely identify a particular Security Association (SA). The SPI is
transmitted from the remote VPN gateway to the local VPN gateway. The local VPN
gateway then uses the network, encryption and key values that the administrator
associated with the SPI to establish the tunnel.
Encryption
Algorithm
Select DES, 3DES, AES-128, ES-192 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, 192-bit or
256-bit key. AES is faster than 3DES.
Integrity
Algorithm
Select SHA1 or MD5 from the drop-down list box. MD5 (Message
Digest 5) and SHA1 (Secure Hash Algorithm) 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 SHA1 for maximum security.
Select Diffie-
Hellman Group
for Key
Exchange
You must choose a key group for key exchange in SA setup. 768bit
refers to Diffie-Hellman Group 1 a 768 bit random number. 1024bit
refers to Diffie-Hellman Group 2 a 1024 bit (1Kb) random number.
Other options include 1536, 2048, and 3072 bit Diffie-Hellman
groups.
Key Life Time
(Seconds)
Define the length of time before an IKE or IPSec SA automatically
renegotiates in this field. It may range from 1 to 2,000,000,000
seconds.
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.
Apply Click Apply/Save to save your changes and return to the IPSec
screen.
Cancel Click Cancel to exit this screen without saving.
Table 87 Settings > Add/Edit: Auto(IKE)
LABEL DESCRIPTION