User's Manual

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3.5.3 NAT Setting
Network Address Translation is the process where a network device, usually a firewall, assigns a public address to a
device or group of devices inside a private network. The main use of NAT is to limit the number of public IP addresses
an organization or company must use, for both economic and security purposes. The simple type of NAT provides
one to one translation of IP address. It can be used to interconnect two IP networks, normally one network is for
Local Area Network and the other network is for Wide Area Network/Internet. To support this function, there are
two ways to do it, by using Source Network Address Translation (SNAT), Destination Network Address Translation
(DNAT). Basically, Network Address Translation (NAT) occurs when one of the IP addresses in an IP packet header is
changed. In a SNAT, the destination IP address is maintained and the source IP address is changed. Most commonly, a
SNAT allows a host on the “inside” of the NAT, in an RFC 1918 IP address space, to initiate a connection to a host on
the “outside” of the NAT. It supports the Port Forwarding, DMZ and 1 to 1 NAT configuration. A DNAT, by way of
contrast, occurs when the destination address is changed and the source IP address is maintained. A DNAT allows a
host on the “outside” to connect to a host on the “inside”. In both cases, the NAT has to maintain a connection table
which tells the NAT where to route returning packets. An important difference between a SNAT and a DNAT is that a
SNAT allows multiple hosts on the “inside” to get to any host on the “outside”. By way of contrast, a DNAT allows any
host on the “outside” to get to a single host on the “inside”. It is supported in NAPT and 1 to 1 NAT features.
To configure the NAT Setting, the Port Forwarding, DMZ, Port Mapping Policy and 1 to 1 NAT configuration page are
provided in this section.
Port Forwarding
By configuring this table, it allows user to automatically redirect common network services to a specific machine
behind the NAT firewall. Select Enable to activate Port Forwarding function and then input all of the parameters to
configure the port forwarding.