IP address

Configuring Network Connections
Appendix A, Configuration parameters

IP address

The ``IP address'' identifies and differentiates a given machine from all others on the network. It consists of a 32-bit binary number that is usually displayed as four octets expressed in decimal and separated by periods. You must have a unique IP address for each machine on the network. In addition, if your machine serves as a router to another network (it contains two or more network adapters and belongs to two or more networks), you must assign each adapter a unique IP address on the appropriate network.

NOTE: The IP address differs from a MAC (Media Access Control) address in that it is configurable. A MAC address is a 6-byte address that is unique to each physical network adapter. This non-configurable address is assigned by the adapter manufacturer.

The IP address consists of two parts: a network address that identifies the network and a host address that identifies the particular host, or node.

Table A-2 IP address derivation

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 binary (32-bit)   1 0 0 0 0 1 0 0 1 0 0 0 1 1 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0
 binary (octets)   1 0 0 0 0 1 0 0   1 0 0 0 1 1 1 1   0 0 0 0 0 0 1 0   0 0 0 0 0 0 1 0
 decimal octets    10                0                 2                 2
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                      IP address (in standard notation) = 10.0.2.2

Several classes of TCP/IP networks are available, each based on the number of hosts a network needs. Network classes supported by SCO are Class A, B, and C. Use the smallest network class that can accommodate all of your network's hosts. Most TCP/IP installations use Class C, but some larger installations might need to use Class B.

Table A-3 Internet address classes

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 Class      Available Hosts   Valid Address
            per Network       Ranges
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 A          16777216          1.0.0.1 through 126.255.255.254
 B          65534             128.0.0.1 through 191.255.255.254
 C          254               192.0.0.1 through 222.255.255.254
 Reserved                     224.0.0.0 through 255.255.255.254

If you are connecting your machine to a pre-existing network, the network address (for Class A, the first octet; for Class B, the first two octets; and for Class C, the first three octets) is the same as those of other machines on the network. In this case, you only need to create a unique host address.

If you are creating an entirely new network and you want to connect to the Internet, you need to contact the Network Information Center (NIC) to have a network address assigned; see ``Domain name'' for the Network Information Center address. If you do not want to connect to an outside network, you can choose any network address that conforms to the syntax shown previously. In either case, once you determine the network address, you can then create the unique host address.

When you determine the IP address, remember:

Each logical network must have its own network address.
All hosts in a network must have the same network address.
All hosts in a network must have unique host addresses.
Do not use these network addresses: 0 or 127 (Class A), 191.255 (Class B), 223.255.255 (Class C), or any of the addresses shown in the Reserved class of Table A-3, ``Internet address classes''.