ZyXEL nbg-5715 Guia Do Utilizador

Chapter 18 IPSec VPN

NBG5715 User’s Guide

Manual key management is useful if you have problems with IKE key management.

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.

Key Group

You must choose a key group for phase 1 IKE setup. DH1 refers to Diffie-
Hellman Group 1 a 768 bit random number. DH2 refers to Diffie-Hellman Group 
2 a 1024 bit (1Kb) random number. 

Phase 2

Encapsulation 
Mode

Select Tunnel mode or Transport mode from the drop-down list box. 

IPSec Protocol

Select the security protocols used for an SA. 

Both AH and ESP increase processing requirements and communications 
latency (delay). 

If you select ESP here, you must select options from the Encryption 
Algorithm and Authentication Algorithm fields (described below).

Encryption 

Algorithm

Select which key size and encryption algorithm to use for data communications. 
Choices are:

DES - a 56-bit key with the DES encryption algorithm

3DES - a 168-bit key with the DES encryption algorithm

The NBG5715 and the remote IPSec router must use the same algorithms and 
key , which can be used to encrypt and decrypt the message or to generate and 
verify a message authentication code. Longer keys require more processing 
power, resulting in increased latency and decreased throughput.

Authentication 

Algorithm

Select which hash algorithm to use to authenticate packet data. Choices are 
SHA1 and MD5. SHA1 is generally considered stronger than MD5, but it is also 
slower.

SA Life Time

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. 

Key Group

You must choose a key group for phase 1 IKE setup. DH1 refers to Diffie-
Hellman Group 1 a 768 bit random number. DH2 refers to Diffie-Hellman Group 
2 a 1024 bit (1Kb) random number. 

Back

Click Back to return to the previous screen.

Apply

Click Apply to save your changes back to the NBG5715.

Cancel

Click Cancel to restore your previous settings.

Security > IPSec VPN > General > Edit: IKE (continued)