UTT Technologies Chapter 7 Advanced
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internal IP addresses to the outside world.
7.1.1.3 NAT Types
The Router provides two types of NAT:
One2One
and
EasyIP
.
●
One2One (One to One):
It indicates static network address translation. It is always
referred to as Basic NAT, which provides a one to one mapping between an internal
and an external IP address. In this type of NAT, IP address needs to be changed, but
port needn
’t.
One to One NAT can be used to allow the outside users to access a LAN server: In the
local network, the LAN server still use the private IP address, which is provided to the
local computers to access; and on the Internet, the Router 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 Router.
●
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 Router
must maintain a translation table so that return packets can be correctly translated
back.
When you obtain multiple public IP addresses from your ISP, you can create more than
one NAT rule for either type of NAT. In actual network environment, the two types of NAT
rules are often used together.
7.1.1.4 Port Forwarding and DMZ Host
When NAT is enabled on the Router, the Router will block all the requests initiated from
outside users. However, in some cases, the outside users want to access the LAN internal
servers through the Router. To achieve this purpose, you need to configure port
forwarding entries or DMZ host on the Router.
1. Port Forwarding
Port forwarding feature allows you to create the mapping between <external IP address:
external port> and <internal IP address: internal port>, then all the requests from outside
users to the specified external IP address: port on the Router will be forwarded to the
mapped local server, so the outside users can access the service offered by the server.
