ZyXEL ZyWALL ATP700 User Guide - Page 454

Chapter 19 IPSec VPN • 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 Zyxel Device to forward some packets from the remote network to a specific computer in the local network. For example, in Figure 319 on page 453, 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 Zyxel Device checks these rules similar to the way it checks rules for a security policy. 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 319 on page 453, 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 319 on page 453, 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. IPSec VPN Example Scenario Here is an example site-to-site IPSec VPN scenario. Figure 320 Site-to-site IPSec VPN Example ZyWALL ATP Series User's Guide 454