ZyXEL Communications P-873HNU-51B, User Manual

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P-873HNU(P)-51B User’s Guide
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H A P T E R
11
Network Address Translation (NAT)
11.1 Overview
This chapter discusses how to configure NAT on the VDSL Router. 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 to a different IP address known within
another network.
11.1.1 What You Can Do in this Chapter
• Use the Port Forwarding screen to configure forward incoming service requests to the server(s)
on your local network ( Section 11.2 on page 154 ).
• Use the Applications screen to forward incoming service requests to the server(s) on your local
network ( Section 11.3 on page 157 ).
• Use the Port Triggering screen to add and configure the VDSL Router’s trigger port settings
( Section 11.4 on page 158 ).
• Use the DMZ screen to configure a default server ( Section 11.5 on page 161 ).
• Use the ALG screen to enable and disable the SIP (VoIP) ALG in the VDSL Router ( Section 11.6
on page 162 ).
• Use the Sessions screen to limit the number of concurrent NAT sessions all clients can use
( Section 11.7 on page 162 ).
11.1.2 What You Need To Know
Inside/Outside
Inside/outside denotes where a host is located relative to the VDSL Router, for example, the
computers of your subscribers are the inside hosts, while the web servers on the Internet are the
outside hosts.
Global/Local
Global/local denotes the IP address of a host in a packet as the packet traverses a router, for
example, the local address refers to the IP address of a host when the packet is in the local
network, while the global address refers to the IP address of the host when the same packet is
traveling in the WAN side.
NAT
In the simplest form, NAT changes the source IP address in a packet received from a subscriber
(the inside local address) to another (the inside global address) before forwarding the packet to the