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Chapter 7 LAN Setup
IAD User’s Guide
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7.3.1 IP Address and Subnet Mask
Similar to the way houses on a street share a common street name, so too do
computers on a LAN share one common network number.
Where you obtain your network number depends on your particular situation. If
the ISP or your network administrator assigns you a block of registered IP
addresses, follow their instructions in selecting the IP addresses and the subnet
mask.
If the ISP did not explicitly give you an IP network number, then most likely you
have a single user account and the ISP will assign you a dynamic IP address when
the connection is established. If this is the case, it is recommended that you select
a network number from 192.168.0.0 to 192.168.255.0 and you must enable the
Network Address Translation (NAT) feature of the IAD. The Internet Assigned
Number Authority (IANA) reserved this block of addresses specifically for private
use; please do not use any other number unless you are told otherwise. Let's say
you select 192.168.1.0 as the network number; which covers 254 individual
addresses, from 192.168.1.1 to 192.168.1.254 (zero and 255 are reserved). In
other words, the first three numbers specify the network number while the last
number identifies an individual computer on that network.
Once you have decided on the network number, pick an IP address that is easy to
remember, for instance, 10.0.0.138, for your IAD, but make sure that no other
device on your network is using that IP address.
The subnet mask specifies the network number portion of an IP address. Your IAD
will compute the subnet mask automatically based on the IP address that you
entered. You don't need to change the subnet mask computed by the IAD unless
you are instructed to do otherwise.
7.3.1.1 Private IP Addresses
Every machine on the Internet must have a unique address. If your networks are
isolated from the Internet, for example, only between your two branch offices, you
can assign any IP addresses to the hosts without problems. However, the Internet
Assigned Numbers Authority (IANA) has reserved the following three blocks of IP
addresses specifically for private networks:
• 10.0.0.0 — 10.255.255.255
• 172.16.0.0 — 172.31.255.255
• 192.168.0.0 — 192.168.255.255
You can obtain your IP address from the IANA, from an ISP or it can be assigned
from a private network. If you belong to a small organization and your Internet
access is through an ISP, the ISP can provide you with the Internet addresses for