Mac Addresses And Address Resolution Protocol - NETGEAR DG834GT Reference Manual

Reference Manual for the Model DG834GT 108 Mbps Super Wireless ADSL Router
192.168.0.2
192.168.0.3
192.168.0.4
192.168.0.5
Figure 8-3: Single IP Address Operation Using NAT
This scheme offers the additional benefit of firewall-like protection because the internal LAN
addresses are not available to the Internet through the translated connection. All incoming
inquiries are filtered out by the router. This filtering can prevent intruders from probing your
system. However, using port forwarding, you can allow one PC (for example, a Web server) on
your local network to be accessible to outside users.

MAC Addresses and Address Resolution Protocol

An IP address alone cannot be used to deliver data from one LAN device to another. To send data
between LAN devices, you must convert the IP address of the destination device to its media
access control (MAC) address. Each device on an Ethernet network has a unique MAC address,
which is a 48-bit number assigned to each device by the manufacturer. The technique that
associates the IP address with a MAC address is known as address resolution. Internet Protocol
uses the Address Resolution Protocol (ARP) to resolve MAC addresses.
If a device sends data to another station on the network and the destination MAC address is not yet
recorded, ARP is used. An ARP request is broadcast onto the network. All stations on the network
receive and read the request. The destination IP address for the chosen station is included as part of
the message so that only the station with this IP address responds to the ARP request. All other
stations discard the request.
B-8
Private IP addresses
assigned by user
192.168.0.1 172.21.15.105
August 2004
IP addresses
assigned by ISP
Internet
7786EA
Network and Routing Basics