ZyXEL Communications USG40 User Manual page 561

It takes several steps to establish an IKE SA. The negotiation mode determines how many. There
are two negotiation modes--main mode and aggressive mode. Main mode provides better security,
while aggressive mode is faster.
Note: Both routers must use the same negotiation mode.
These modes are discussed in more detail in
various examples in the rest of this section.
The ZyWALL/USG supports IKEv1 and IKEv2. See
IP Addresses of the ZyWALL/USG and Remote IPSec Router
To set up an IKE SA, you have to specify the IP addresses of the ZyWALL/USG and remote IPSec
router. You can usually enter a static IP address or a domain name for either or both IP addresses.
Sometimes, your ZyWALL/USG might offer another alternative, such as using the IP address of a
port or interface, as well.
You can also specify the IP address of the remote IPSec router as 0.0.0.0. This means that the
remote IPSec router can have any IP address. In this case, only the remote IPSec router can initiate
an IKE SA because the ZyWALL/USG does not know the IP address of the remote IPSec router. This
is often used for telecommuters.
IKE SA Proposal
The IKE SA proposal is used to identify the encryption algorithm, authentication algorithm, and
Diffie-Hellman (DH) key group that the ZyWALL/USG and remote IPSec router use in the IKE SA. In
main mode, this is done in steps 1 and 2, as illustrated next.
Figure 384 IKE SA: Main Negotiation Mode, Steps 1 - 2: IKE SA Proposal
X
The ZyWALL/USG sends one or more proposals to the remote IPSec router. (In some devices, you
can only set up one proposal.) Each proposal consists of an encryption algorithm, authentication
algorithm, and DH key group that the ZyWALL/USG wants to use in the IKE SA. The remote IPSec
router selects an acceptable proposal and sends the accepted proposal back to the ZyWALL/USG. If
the remote IPSec router rejects all of the proposals, the ZyWALL/USG and remote IPSec router
cannot establish an IKE SA.
Note: Both routers must use the same encryption algorithm, authentication algorithm,
and DH key group.
Chapter 29 IPSec VPN
Negotiation Mode on page
One or more proposals, each one consisting of:
- encryption algorithm
- authentication algorithm
- Diffie-Hellman key group
1
2
ZyWALL/USG Series User's Guide
561
564. Main mode is used in
Section 29.1 on page 534
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for more information.