ZyXEL Communications 792H manual 14.12Manual Key Setup, Security Parameter Index SPI

	Prestige 792H G.SHDSL Router
	Table 14-8 VPN IKE: Advanced
LABEL	DESCRIPTION
Authentication	Select SHA1 or MD5 from the drop-down list box. MD5 (Message Digest 5) and
Algorithm	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 SHA-1for maximum security.
SA Life Time	Define the length of time before an IKE SA automatically renegotiates in this field. It
(Seconds)	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.
Encapsulation	Select Tunnel mode or Transport mode from the drop-down list box.
Perfect Forward	Perfect Forward Secrecy (PFS) is disabled (None) by default in phase 2 IPSec SA
Secrecy (PFS)	setup. This allows faster IPSec setup, but is not so secure. Choose DH1 or DH2 from
	the drop-down list box to enable PFS. 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 (more secure, yet slower).
Apply	Click Apply to save your changes back to the Prestige and return to the VPN IKE
	screen.
Cancel	Click Cancel to return to the VPN IKE screen without saving your changes.

14.12Manual Key Setup

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

14.12.1Security 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.

VPN Screens 14-19