Dynalink RTA770 - Manual (Page 100)

ADSL Router User Manaul
88
NAT (Network Address Translation) IP Address
NAT is an Internet standard that translates a private IP within one network to a public IP
address, either a static or dynamic one. NAT provides a type of firewall by hiding internal IP
addresses. It also enables a company to use more internal IP addresses.
If the IP addresses given by your ISP are not enough for each PC on the LAN and the ADSL
Router, you need to use NAT. With NAT, you make up a private IP network for the LAN and
assign an IP address from that network to each PC. One of some public addresses is
configured and mapped to a private workstation address when accesses are made through
the gateway to a public network.
For example, the ADSL Router is assigned with the public IP address of 168.111.2.1. With
NAT enabled, it creates a Virtual LAN. Each PC on the Virtual LAN is assigned with a private
IP address with default value of 192.168.1.2 to 192.168.2.254. These PCs are not
accessible by the outside world but they can communicate with the outside world through
the public IP 168.111.2.1.
Private IP Address
Private IP addresses are also LAN IP addresses, but are considered “illegal” IP addresses to
the Internet. They are private to an enterprise while still permitting full network layer
connectivity between all hosts inside an enterprise as well as all public hosts of different
enterprises.
The ADSL Router uses private IP addresses by assigning them to the LAN that cannot be
directly accessed by the Internet or remote server. To access the Internet, private network
should have an agent to translate the private IP address to public IP address.
Public IP Address
Public IP addresses are LAN IP addresses that can be considered “legal” for the Internet,
because they can be recognized and accessed by any device on the other side of the DSL
connection. In most cases they are allocated by your ISP.
If you are given a range of fixed IP addresses, then one can be assigned to the router and
the others to network devices on the LAN, such as computer workstations, ftp servers, and
web servers.
PVC (Permanent Virtual Circuit)
A PVC is a logical point-to-point circuit between customer sites. PVCs are low-delay circuits
because routing decisions do not need to be made along the way. Permanent means that
the circuit is preprogrammed by the carrier as a path through the network. It does not
need to be set up or turned down for each session.
RIP (Routing Information Protocol)
RIP is a routing protocol that uses the distance-vector routing algorithms to calculate
least-hops routes to a destination. It is used on the Internet and is common in the NetWare
environment. It exchanges routing information with other routers. It includes V1, V2 and
V1&V2, which controls the sending and receiving of RIP packets over Ethernet.
UDP (User Datagram Protocol)
UDP is a connectionless transport service that dispenses with the reliability services
provided by TCP. UDP gives applications a direct interface with IP and the ability to address
a particular application process running on a host via a port number without setting up a
connection session.