User's Manual

UTT Technologies Chapter 8 NAT
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local network, the LAN server still use the private IP address, which is provided to the
LAN hosts to access; and on the Internet, the Device will assign an external IP address
to the local server, then the outside users can using this external IP address to access
the server through the Device.
Ɣ EasyIP: It indicates network address and port translation (NAPT). Since it is the most
common type of NAT, it is often simply referred to as NAT. NAPT provides many-to-one
mappings between multiple internal IP addresses and a single external IP addresses,
that is, these multiple internal IP addresses will be translated to the same external IP
address. In this type of NAT, to avoid ambiguity in the handling of returned packets, it
must dynamically assign a TCP/UDP port to an outgoing session and change the
packets¶ source port to the assigned port before forwarding them. Besides, the Device
must maintain a translation table so that return packets can be correctly translated
back.
Ɣ Passthrough: It indicates bypassing NAT when NAT is enabled. If you enable NAT, the
LAN hosts must match a NAT rule when accessing outside hosts. So if you do not want
to perform NAT for some LAN hosts, you can use this function to bypass NAT for those
hosts. It is often used for some particular applications that do not support NAT well,
such as, online game or video conferencing. To ensure that these applications run
properly, you can divide a voice and video area in the LAN, and create a
Passthrough NAT rule for the hosts in this area. Then the Device will not perform
NAT for them, that is, the packets sent by these hosts to the outside hosts will be
directly routed and forwarded.
When you obtain multiple public IP addresses from your ISP, you can create more than one
NAT rule for each type of NAT. In actual network environment, different types of NAT rules are
often used together.
8.3.1.3 The Relations of Internet Connection, NAT Rule and
Port Forwarding Rule
On the Device, the relations of the Internet connection, NAT rule and port forwarding rule
are as follows:
Ɣ A NAT rule should be bound to an Internet connection. It allows you bind multiple NAT
rules to the same Internet connection.
Ɣ A port forwarding rule should be bound to an EasyIP NAT rule (that is, the NAT rule¶s
type is EasyIP), and the port forwarding rule will use the NAT UXOH¶s external IP address