ZyXEL ISG50-PSTN User Guide - Page 395

Chapter 24 IPSec VPN Destination Address in Inbound Packets (Inbound Traffic, Destination NAT) You can set up this translation if you want the ISG50 to forward some packets from the remote network to a specific computer in the local network. For example, in Figure 258 on page 394, 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). You have to specify one or more rules when you set up this kind of NAT. The ISG50 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 258 on page 394, 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 258 on page 394, 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. ISG50 User's Guide 395