ZyXEL Communications ZyWALL 110 User Manual page 418

• Source address in outbound packets - this translation is necessary if you want the ZyWALL/USG
to route packets from computers outside the local network through the IPSec SA.
• Source address in inbound packets - this translation hides the source address of computers in the
remote network.
• Destination address in inbound packets - this translation is used if you want to forward packets
(for example, mail) from the remote network to a specific computer (like the mail server) in the
local network.
Each kind of translation is explained below. The following example is used to help explain each one.
Figure 274 VPN Example: NAT for Inbound and Outbound Traffic
Source Address in Outbound Packets (Outbound Traffic, Source NAT)
This translation lets the ZyWALL/USG route packets from computers that are not part of the
specified local network (local policy) through the IPSec SA. For example, in
418, you have to configure this kind of translation if you want computer M to establish a connection
with any computer in the remote network (B). If you do not configure it, the remote IPSec router
may not route messages for computer M through the IPSec SA because computer M's IP address is
not part of its local policy.
To set up this NAT, you have to specify the following information:
• Source - the original source address; most likely, computer M's network.
• Destination - the original destination address; the remote network (B).
• SNAT - the translated source address; the local network (A).
Source Address in Inbound Packets (Inbound Traffic, Source NAT)
You can set up this translation if you want to change the source address of computers in the remote
network. To set up this NAT, you have to specify the following information:
• Source - the original source address; the remote network (B).
Chapter 22 IPSec VPN
ZyWALL/USG Series User's Guide
418
Figure 274 on page