Siemens E-110-I - Manual (Page 87)

Chapter 7: Glossary
Chapter 7: Glossary
• ARP (Address Resolution Protocol )
ARP is a TCP/IP protocol for mapping an IP address to a physical machine address that is recognized in
the local network, such as an Ethernet address.
A host wishing to obtain a physical address broadcasts an ARP request onto the TCP/IP network. The
host on the network that has the IP address in the request then replies with its physical hardware
address.
Inverse ARP (In-ARP), on the other hand, is used by a host to discover its IP address. In this case, the
host broadcasts its physical address and a RARP server replies with the host's IP address.
• DHCP (Dynamic Host Configuration Protocol)
When operates as a DHCP server, the ADSL Router assign IP addresses to the client PCs on the LAN.
The client PCs “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 DHCP IP address can be a single, fixed public IP address, an ISP assigned public IP address, or a
private IP address.
If you enable DHCP server on a private 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. By this, the client PCs are able to access the Internet.
• LAN (Local Area Network) & WAN (Wide Area Network)
A LAN is a computer network limited to the immediate area, usually the same building or floor of a
building. A WAN, on the other hand, is an outside connection to another network or the Internet.
The Ethernet side of the ADSL Router is called the LAN port. It is a twisted-pair Ethernet 10Base-T
interface. A hub can be connected to the LAN port. More than one computers, such as server or
printer, can be connected through this hub to the ADSL Router and composes a LAN.
The DSL port of the ADSL Router composes the WAN interface, which supports PPP or RFC 1483
connecting to another remote DSL device.
• 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 word 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.
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