User's Manual

Chapter 20 IPSec VPN
ZyWALL USG 100/200 Series User’s Guide
382
Figure 266 VPN Example: NAT for Inbound and Outbound Traffic
Source Address in Outbound Packets (Outbound Traffic, Source NAT)
This translation lets the ZyWALL route packets from computers that are not part of the
specified local network (local policy) through the IPSec SA. For example, in Figure 266 on
page 382, 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).
• Destination - the original destination address; the local network (A).
• SNAT - the translated source address; a different IP address (range of addresses) to hide
the original source address.
Destination Address in Inbound Packets (Inbound Traffic, Destination NAT)
You can set up this translation if you want the ZyWALL to forward some packets from the
remote network to a specific computer in the local network. For example, in Figure 266 on
page 382, you can configure this kind of translation if you want to forward mail from the
remote network to the mail server in the local network (A).