ZyXEL Communications ZyWall USG 2000 User Manual page 283

However, you need to configure NAT loopback for LAN users to use a domain
name to access the server.
Figure 175 LAN Computer Queries the DNS Server
A LAN1 user computer at IP address 192.168.1.89 queries the domain name
(xxx.LAN-SMTP.com in this example) from a public DNS server and gets the SMTP
server's 1-1 NAT mapped public IP address of 1.1.1.1.
NAT Loopback Virtual Server
When a LAN user sends SMTP traffic to IP address 1.1.1.1, the traffic comes into
the ZyWALL through the LAN interface, thus it does not match the NAT 1:1
ZyWALL USG 2000 User's Guide
xxx.LAN-SMTP.com = ?
1.1.1.1
LAN
192.168.1.21
Chapter 16 Virtual Servers
DNS
xxx.LAN-SMTP.com = 1.1.1.1
192.168.1.89
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