SBG3500-N Series User’s Guide
203
CHAPTER 11
Network Address Translation (NAT)
11.1 Overview
This chapter discusses how to configure NAT on the SBG3500-N Series. 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 204).
•Use the Applications screen to forward incoming service requests to the server(s) on your local
network (Section 11.3 on page 207).
•Use the Port Triggering screen to add and configure the SBG3500-N Series’s trigger port
settings (Section 11.4 on page 208).
•Use the Default Server screen to configure a default server (Section 11.5 on page 211).
•Use the ALG screen to enable and disable the NAT and SIP (VoIP) ALG in the SBG3500-N Series
(Section 11.6 on page 212).
•Use the Address Mapping screen to configure the SBG3500-N Series's address mapping
settings (Section 11.7 on page 212).
11.1.2 What You Need To Know
Inside/Outside
Inside/outside denotes where a host is located relative to the SBG3500-N Series, 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
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