ZyXEL P-660N-T1A User Guide - Page 151
Network Address Translation NAT
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CHAPTER 9 Network Address Translation (NAT) 9.1 Overview This chapter discusses how to configure NAT on the ZyXEL Device. 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. 9.1.1 What You Can Do in the NAT Screens • Use the NAT General Setup screen (Section 9.2 on page 152) to configure the NAT setup settings. • Use the Port Forwarding screen (Section 9.3 on page 153) to configure forward incoming service requests to the server(s) on your local network. • Use the Address Mapping screen (Section 9.4 on page 156) to change your ZyXEL Device's address mapping settings. • Use the ALG screen (Section 9.5 on page 158) to enable and disable the SIP (VoIP) ALG in the ZyXEL Device. 9.1.2 What You Need To Know About NAT Inside/Outside Inside/outside denotes where a host is located relative to the ZyXEL Device, 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 WAN side. When the response comes back, NAT translates the destination address (the inside global address) back to the inside local address before forwarding it to the original inside host. ADSL Router Series User's Guide 151