IP address: network portion
Network addresses are managed by an organization in Norfolk, Virginia, recognized as InterNIC.
InterNIC has been contracted by the National Science Foundation to manage the Internet addresses
and domains. Network addresses are distributed to organizations that are in turn responsible for
making sure all attached devices or hosts on the network are properly numbered. For more
information on the network portion of an IP address, see
Default IP address configuration (AutoIP)
and
Subnets in this section.
IP address: host portion
Host addresses numerically identify specific network interfaces on an IP network. Usually a host has
only one network interface; thus, only one IP address. Because no two devices can share the same
number at the same time, administrators typically maintain address tables to assure correct
assignment of addresses in the host network.
IP address structure and class
An IP address is comprised of 32 bits of information and divided into 4 sections containing 1 byte
each section or 4 bytes total:
xxx.xxx.xxx.xxx
For efficiency in routing, networks were broken down into three classes, so routing can begin simply
by identifying the leading byte of information in the IP address. The three IP addresses that InterNIC
assigns are class A, B, and C. The network class determines what each of the four IP address
sections identify as shown below:
Table 8-5 IP address class format
Class First Address Byte
xxx.
Second Address
Byte xxx.
Third Address Byte
xxx.
Fourth Address Byte
xxx
A Network. Host. Host. Host.
B Network. Network. Host. Host.
C Network. Network. Network. Host.
As illustrated in Table 8-6 Network class characteristics, each network class differs by the leading bit
identifier, the address range, the number of each type available, and the maximum number of hosts
each class allows.
Table 8-6 Network class characteristics
Class Network Class
Characteristics
Address Range Maximum Number of
Networks in the Class
Maximum Hosts in
the Network
A 0 0.0.0.0 to
127.255.255.255.
126. Over 16 Million.
B 10. 128.0.0.0 to
191.255.255.255.
16,382. 65,534.
C 110. 192.0.0.0 to
223.255.255.255.
Over 2 Million. 254.
ENWW TCP/IP 87
