Chapter 21 IPSec

 

Table 87 Settings > Add/Edit: Auto(IKE)

 

LABEL

DESCRIPTION

 

Encryption

Select DES, 3DES, AES-128, ES-192or AES-256from the drop-

 

Algorithm

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

Select SHA1 or MD5 from the drop-down list box. MD5 (Message

 

Algorithm

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-

You must choose a key group for key exchange in SA setup. 768bit

 

Hellman Group

refers to Diffie-Hellman Group 1 a 768 bit random number. 1024bit

 

for Key

refers to Diffie-Hellman Group 2 a 1024 bit (1Kb) random number.

 

Exchange

Other options include 1536, 2048, and 3072 bit Diffie-Hellman

 

 

groups.

 

 

 

 

Key Life Time

Define the length of time before an IKE or IPSec SA automatically

 

(Seconds)

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.

 

 

 

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.

 

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VSG1432-B101 Series User’s Guide