What is a network? 143

If your LAN will not connect to the public Internet, you can set up your own unique (that is, private) IP address numbering. IP addresses for private networks such as an office LAN must also be unique but only within that LAN.

What is DHCP? Dynamic Host Configuration Protocol is a process that automatically assigns a unique, temporary IP address to a newly attached computer on an IP network.

What is DNS? The Domain Name System translates the common alphabetic name into the numeric IP address. For example, www.3com.com is translated to an specific IP address by DNS. If you do not use the DHCP functionality of the Dual 56K LAN Modem, you will have to manually configure the following parameters for each computer on the LAN: IP address, subnet mask, DNS address and default gateway.

What is NAT? Network Address Translation, or NAT—also known as IP address sharing—is a system of IP address translation that allows multiple users to share a single WAN connection, such as an Internet connection.

As an example, if you configure the Dual 56K LAN Modem for dial-out access to the Internet, leaving NAT enabled, when any user on the LAN launches a Web browser for Internet access, his or her computer’s local (not publicly-routable) IP address is translated into the (publicly-routable) IP address provided by the ISP for access. This allows multiple users on your LAN to appear to your ISP as a single user or single connection.

In the case of a LAN Modem dial-in scenario, in which one LAN Modem is configured to receive incoming calls and a second LAN Modem is configured for dial-out access to the first LAN Modem using NAT, NAT allows multiple users attached to the second LAN Modem to appear as a single user to the first LAN Modem.

In terms of communication between the workstations on either LAN, the use of NAT means that workstations on the second, client-side LAN can directly access all workstations on the server-side LAN, but that, conversely, workstations on the server-side LAN cannot directly access all workstations on the client-side LAN. This is because, in effect, the server-side LAN Modem does not “see” that there are multiple workstations hidden behind the client-side LAN Modem. The translation of local IP addresses to a publicly-routable IP address only occurs if the client-side LAN Modem has initiated the call.

You probably do not want to use NAT If your LAN network is static; that is, an IP address is assigned to your computer by your MIS department or ISP and is manually configured.

What are numbered and Some networks require an IP address to be assigned to a WAN in addition to the unnumbered links? LAN(s). If a WAN has an IP address assigned to it, it is considered a numbered link.

If there is not an IP address assigned to a WAN, it is considered to be an unnumbered link.

How is overall The performance of all linked devices must be considered to determine throughput determined? end-to-end throughput. Connection performance is affected by each device in the

chain. Therefore, the slowest link in the chain determines the maximum

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3Com Dual 56K manual What is a network?