Configure DSL interfaces
Digi TransPort User Guide
216
DSL Network Settings parameters
This DSL PVC is using PPP 1
The default interface for DSL. The default interface for DSL is PPP 1.
Description
A description for the DSL. This field is optional.
Username
The ADSL username.
Password
The password for the DSL account.
Confirm password
Enter the password for the DSL account again.
Enable NAT on this interface
Enables or disables IP Network Address Translation (NAT) or Network Address and Port
Translation (NAPT) at the Ethernet interface. When the parameter is set to disabled, no NAT
will take place. When this parameter is enabled, the extra options described below are
displayed.
NAT and NAPT can have many uses, but they are generally used to allow a number of private
IP hosts (PCs for example) to connect to the Internet through a single shared public IP address.
This has two main advantages, it saves on IP address space (the ISP only need assign you one
IP address), and it isolates the private IP hosts from the Internet, effectively providing a simple
firewall because unsolicited traffic from the Internet cannot be routed directly to the private IP
hosts.
To use NAT or NAPT correctly in the example of connecting private hosts to the Internet, NAT
or NAPT should be enabled on the router’s WAN side interface and should be disabled on the
router’s LAN side interface.
IP address
Enable standard Network Address Translation (NAT).
When a private IP host sends a UDP or TCP packet to an Internet IP address, the router
changes the source address of the packet from the private host IP to the router’s public IP
address before forwarding the packet onto the Internet host. Additionally it will create an
entry in a NAT table containing the private IP source address, the private IP port number, the
public IP destination address and the destination port number. Conversely, when the router
receives a reply packet back from the public host, it checks the source IP, source port number
and destination port number in the NAT table to determine which private host to forward the
packet to. Before it forwards the packet back to the private host, it changes the destination IP
address of the packet from its public IP address to the IP address of the private host.
