ZyXEL 793H 사용자 가이드

 Chapter 11 IPSec VPN

P-793H User’s Guide

The IKE SA proposal is used to identify the encryption algorithm, authentication algorithm, 
and Diffie-Hellman (DH) key group that the ZyXEL Device and remote IPSec router use in 
the IKE SA. In main mode, this is done in steps 1 and 2, as illustrated below.

Figure 77   IKE SA: Main Negotiation Mode, Steps 1 - 2: IKE SA Proposal

The ZyXEL Device sends one or more proposals to the remote IPSec router. (In some devices, 
you can set up only one proposal.) Each proposal consists of an encryption algorithm, 
authentication algorithm, and DH key group that the ZyXEL Device wants to use in the IKE 
SA. The remote IPSec router selects an acceptable proposal and sends the accepted proposal 
back to the ZyXEL Device. If the remote IPSec router rejects all of the proposals (for example, 
if the VPN tunnel is not configured correctly), the ZyXEL Device and remote IPSec router 
cannot establish an IKE SA.

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Both routers must use the same encryption algorithm, authentication 
algorithm, and DH key group.

See the field descriptions for information about specific encryption algorithms, authentication 
algorithms, and DH key groups. You can also see 

 for more 

information about the role of DH key groups.

The ZyXEL Device and the remote IPSec router use a DH key exchange to establish a shared 
secret, which is used to generate encryption keys for IKE SA and IPSec SA. In main mode, the 
DH key exchange is done in steps 3 and 4, as illustrated below.

Figure 78   IKE SA: Main Negotiation Mode, Steps 3 - 4: DH Key Exchange

The DH key exchange is based on DH key groups. Each key group is a fixed number of bits 
long. The longer the key, the more secure the encryption keys, but also the longer it takes to 
encrypt and decrypt information. For example, DH2 keys (1024 bits) are more secure than 
DH1 keys (768 bits), but DH2 encryption keys take longer to encrypt and decrypt.