Information Technology Reference
In-Depth Information
Study Guide
Classful and Classless Addressing
One of the ways to characterize routing protocols is either as classful or classless. This is a result of
the evolution from classful to classless IPv4 addressing. As networks began to use classless address-
ing, classless routing protocols had to be modified or developed to include the subnet mask in the
routing update. The exercises in the following section review classful and classless addressing.
Move from Classful to Classless Addressing Exercise
As of January 2007, there were over 433 million hosts on the Internet. Without the introduction of
VLSM
and
CIDR
notation in 1993 (RFC
1519
),
Network Address Translation
(NAT) in 1994 (RFC
1631
), and private addressing in 1996 (RFC
1918
), the IPv4 32-bit address space would now be
exhausted.
High-Order Bits
Class A, B, and C addresses were defined with a specific format for the high-order bits, which are the
leftmost bits in a 32-bit address. Table 6-1 lists the first octet in binary of sample IP addresses. For
each octet, identify the type of address by designating whether it would belong to a Class A, Class B,
Class C, multicast, or experimental address.
Table 6-1
High-Order Bits
First Octet of the Address in Binary
Type of Address
10100010
Class B
11100000
Multicast
01110100
Class A
11110000
Experimental
11001100
Class C
IPv4 Classful Addressing Structure
List the default subnet mask for each class.
Class A: 255.0.0.0
Class B: 255.255.0.0
Class C: 255.255.255.0
In Table 6-2, complete the table by filling in the missing information.
