ZyWALL User's Guide

Chapter 20 IPSec VPN
ZyWALL USG 100/200 Series User’s Guide
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You have to specify one or more rules when you set up this kind of NAT. The ZyWALL
checks these rules similar to the way it checks rules for a firewall. The first part of these rules
define the conditions in which the rule apply.
• Original IP - the original destination address; the remote network (B).
• Protocol - the protocol [TCP, UDP, or both] used by the service requesting the connection.
• Original Port - the original destination port or range of destination ports; in Figure 266 on
page 382, it might be port 25 for SMTP.
The second part of these rules controls the translation when the condition is satisfied.
• Mapped IP - the translated destination address; in Figure 266 on page 382, the IP address
of the mail server in the local network (A).
• Mapped Port - the translated destination port or range of destination ports.
The original port range and the mapped port range must be the same size.