ZyXEL Communications ISG50-ISDN User Manual page 394

Chapter 24 IPSec VPN
• 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 258 VPN Example: NAT for Inbound and Outbound Traffic
Source Address in Outbound Packets (Outbound Traffic, Source NAT)
This translation lets the ISG50 route packets from computers that are not part of the specified local
network (local policy) through the IPSec SA. For example, in
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.
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Figure 258 on page 394, you have to
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