Port Redirection - Draytek Vigor130 User Manual

Public IP address is usually assigned by your ISP, for which you may get charged. Private IP
addresses are recognized only among internal hosts.
When the outgoing packets destined to some public server on the Internet reach the NAT
modem, the modem will change its source address into the public IP address of the modem,
select the available public port, and then forward it. At the same time, the modem shall list
an entry in a table to memorize this address/port-mapping relationship. When the public
server response, the incoming traffic, of course, is destined to the modem's public IP address
and the modem will do the inversion based on its table. Therefore, the internal host can
communicate with external host smoothly.
The benefit of the NAT includes:
Save cost on applying public IP address and apply efficient usage of IP address.
NAT allows the internal IP addresses of local hosts to be translated into one public IP
address, thus you can have only one IP address on behalf of the entire internal hosts.
Enhance security of the internal network by obscuring the IP address. There are
many attacks aiming victims based on the IP address. Since the attacker cannot be
aware of any private IP addresses, the NAT function can protect the internal network.
On NAT page, you will see the private IP address defined in RFC-1918. Usually we use
the 192.168.1.0/24 subnet for the modem. As stated before, the NAT facility can map one
or more IP addresses and/or service ports into different specified services. In other words,
the NAT function can be achieved by using port mapping methods.
Below shows the menu items for NAT.
3 . 3 . 1 P o r t R e d
3 . 3 . 1 P o r t R e d
Port Redirection is usually set up for server related service inside the local network (LAN),
such as web servers, FTP servers, E-mail servers etc. Most of the case, you need a public IP
address for each server and this public IP address/domain name are recognized by all users.
Since the server is actually located inside the LAN, the network well protected by NAT of
the modem, and identified by its private IP address/port, the goal of Port Redirection
function is to forward all access request with public IP address from external users to the
mapping private IP address/port of the server.
Vigor130 Series User's Guide
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