ENWW TCP/IP Overview 239
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 in Table A.1
:
As illustrated in Table A.2
, 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 A.1 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
Table A.2 Network Class Characteristics
Class Leading
Bit
Identifier
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
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