Like houses on a street that share a common street name, the 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.
The Internet Assigned Number Authority (IANA) reserved a block of addresses specifically for private use (refer to Section 4.4.2 “Private IP Addresses” on page 54); 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.
The subnet mask specifies the network number portion of an IP address.
4.4.2 Private IP AddressesEvery 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 your local networks. On the other hand, if you are part of a much larger organization, you should consult your network administrator for the appropriate IP addresses.
Regardless of your particular situation, do not create an arbitrary IP address; always follow the guidelines above.
Note: For more information on address assignment, please refer to RFC 1597, Address Allocation for Private Internets and RFC 1466, Guidelines for Management of IP Address Space.
54 | Chapter 4 LAN, WAN and Server Setup |