User's Manual

NBG-510S User’s Guide
81
CHAPTER 11
NAT and Firewall (WAN to LAN)
This chapter discusses how to configure NAT on the ZyXEL Device.
11.1 NAT Overview
NAT (Network Address Translation - NAT, RFC 1631) changes 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.
11.2 Port Forwarding and Firewall
Incoming sessions (sessions initiated from the WAN and going to the LAN) are blocked by
default. Use port forwarding to allow access from the outside (the Internet) to server(s) on
your LAN.
" Configuring port forwarding also configures the firewall’s WAN to LAN settings.
Port forwarding automatically has the firewall allow unencrypted access from the WAN (the
Internet) to your LAN.
• For secure connections from the Internet to the LAN computers, use the secure remote
user portal (see part VI on page 133).
• To set which services/protocols can access the ZyXEL Device from the WAN (the
Internet), see Section 19.4 on page 129. This allows or disallows remote management of
the ZyXEL Device.
• To control access going from the LAN to the WAN, use the security screens (see part III
on page 91).
A port forwarding set is a list of LAN servers (for example web or FTP) that you can make
accessible to the outside world even though NAT makes your whole inside network appear as
a single machine to the outside world.
In addition to the servers for specified services, NAT supports a default server. A service
request that does not have a server explicitly designated for it is forwarded to the default
server. If the default is not defined, the service request is simply discarded.