Nat; Port Redirection - Draytek VigorPro 5510 Series User Manual

Note: Before you select Strict Bind, you have to bind one set of IP/MAC address for one
PC. If not, no one of the PCs can access into Internet. And the web configurator of the
router might not be accessed.
3 . 3 N A T
3 . 3 N A T
Usually, the router serves as an NAT (Network Address Translation) router. NAT is a
mechanism that one or more private IP addresses can be mapped into a single public one.
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
router, the router will change its source address into the public IP address of the router, select
the available public port, and then forward it. At the same time, the router 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 router's public IP address and the
router 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.
Note: 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 router. 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
3 . 3 . 1 P o r t R e
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 router, 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.
VigorPro5510 Series User's Guide
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