52
User’s Guide
Appendix A: About Configuration Parameters
Telindus 1120 ADSL Router
Primary (Public) IP Address
Primary IP addresses are LAN IP addresses that can be considered “legal” for the
Internet. In most cases they are allocated to you by an ISP. They are called “primary”
because they can be recognized and accessed by any device on the other side of the DSL
connection, such as the Internet.
However, if you are allocated a block of fixed IP addresses, then one can be assigned to
the router and the others can used by other network devices, such as computer
workstations, ftp servers, and web servers. Network devices that use fixed IP addresses
always use the same IP address, and are never dynamically assigned a different one. You
can only run Static IP mode if you have an available block of fixed Public IP addresses to
use.
Additionally, if your block of fixed IP addresses is large enough, you can assign one to the
router, others to network devices, and even use one to define a another range of
Secondary IP addresses. This is known as “mixed mode” since you would be
simultaneously running Primary and Secondary IP addresses.
Secondary (Private) IP Address
Secondary IP addresses are also LAN IP addresses, but are considered “virtual”
addresses that the router allocates to itself and other network devices. They may be
copies of actual, legal Primary IP addresses being used somewhere else on the Internet,
and would then be considered illegal. However, since all IP addresses have to be unique,
there can only be one copy of each address that can be recognized and accessed on a
network or the Internet.
A router uses Private IP addresses by allocating them within a local network that cannot
be directly accessed by the Internet or remote server. To access outside the “private”
network, the Private IP Addresses must pass their data back and forth with an associated
Public IP address. The Public IP address is then used to access the Internet or remote
server.
NAT IP Address
Network Address Translation (NAT) IP Address is a Public IP Address. It can be a single,
fixed Public IP address, or an dynamically assigned Public IP address. NAT is used to
translate Private IP addresses to a Public IP address. Many Private IP addresses can be
translated through the single Public NAT IP address. The router keeps track of all the
translation traffic so that information arriving at the single NAT IP Address can seamlessly
be forwarded to the appropriate Private IP address.
DHCP IP Address Assignment
Dynamic Host Control Protocol (DHCP) IP Address Assignment is a method the router
uses to dynamically assign Private IP addresses within its local network. The router has a
subnet (range) of available Private IP addresses with which to assign to other network
devices on its local network. It “leases” these Private IP addresses for a user-defined
amount of time. After the lease time expires, the Private IP address is made available for
assigning to other network devices.
The subnet of Private IP addresses that the router assigns are based on a single DHCP IP
Address. All traffic going to and from the subnet of Private IP addresses goes through the
DHCP IP Address. The DHCP IP Address can be a single, fixed Public IP address, an ISP
assigned Public IP address, or a Private IP address.
For situations where a Private IP address is assigned as the DHCP IP Address, a Public
IP address will have to be assigned to the NAT IP Address, and NAT has to be enabled so
that the DHCP IP Address can be translated into a Public IP address.
Numbered IP Address
When negotiating a connection, you can either let the remote server or ISP assign the
Telindus 1120 ADSL Router a WAN IP address, or you can specify your own WAN IP
address.