Nat; Chapter 9 Nat; Nat Overview; What You Can Do In This Chapter - ZyXEL Communications USG FLEX H Series User Manual

9.1 NAT Overview

NAT (Network Address Translation - NAT, RFC 1631) is the translation of the IP address of a host in a
packet. For example, the source address of an outgoing packet, used within one network is changed to
a different IP address known within another network. Use Network Address Translation (NAT) to make
computers on a private network behind the Zyxel Device available outside the private network. If the
Zyxel Device has only one public IP address, you can make the computers in the private network
available by using ports to forward packets to the appropriate private IP address.
Suppose you want to assign ports 21-25 to one FTP, Telnet and SMTP server (A in the example), port 80 to
another (B in the example) and assign a default server IP address of 192.168.1.35 to a third (C in the
example). You assign the LAN IP addresses and the ISP assigns the WAN IP address. The NAT network
appears as a single host on the Internet.
Figure 105 Multiple Servers Behind NAT Example

9.1.1 What You Can Do in this Chapter

Use the NAT screens (see
configuration details. You can also create new NAT rules and edit or delete existing ones.

9.1.2 What You Need to Know

NAT is also known as virtual server, port forwarding, or port translation.
Well-known Ports
Port numbers range from 0 to 65535, but only port numbers 0 to 1023 are reserved for privileged services
and designated as well-known ports. The following list specifies the ports used by the server process as its
contact ports. See
about service objects.
Section 9.2 on page
Section 14.2 on page 216
USG FLEX H Series User's Guide
C
150) to view and manage the list of NAT rules and see their
(Configuration > Object > Service) for more information
147
H A P T E R

NAT

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