2(2)T on May 14, 2001.
Note
For more information on IPv6, refer to http://www.cisco.com/go/ipv6.
Note
This chapter focuses only on the IPv4 addresses, which are referred to as IP addresses.
Classes of IP Addresses
The Internet Assigned Numbers Authority (IANA) grouped IP addresses into the following classes. Each class has
its own requirements and purpose:
Class A
Class B
Class C
Class D
Class E
Understanding IP Address Classes
Class A??”0NNNNNNN.HHHHHHHH.HHHHHHHH.HHHHHHHH
First octet represents the network address and the remaining three octets represent the host
address.
First high order bit is set to 0.
7 network bits.
24 host bits.
First byte range: 0??“127.
126 Class A ranges exist (0 and 127 are reserved).
16,777,214 hosts are on each Class A.
Example: Host 10.0.0.1 on network 10.0.0.0
Class B??”10NNNNNN.NNNNNNNN.HHHHHHHH.HHHHHHHH
First two octets represent the network address and the remaining two octets represent the host
address.
First two high order bits are set to 1 and 0, respectively.
14 network bits.
16 host bits.
First byte range: 128??“191.
16,384 Class B ranges exist.
65,532 hosts are on each Class B.
Example: Host 128.10.1.5 on network 128.10.
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