3Com 3C888 - OfficeConnect Dual 56K LAN Modem Router User Manual Download

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What is a network?

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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

unnumbered links?

Some networks require an IP address to be assigned to a WAN in addition to the
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

throughput determined?

The performance of all linked devices must be considered to determine
end-to-end throughput. Connection performance is affected by each device in the
chain. Therefore, the slowest link in the chain determines the maximum