D-Link DES-3326 User Manual - Address Classes
DES-3326 Layer 3 Fast Ethernet Switch User’s Guide
70
Switch Management and Operating Concepts
which part belongs to the destination and which part belongs to the
network.
Address Classes
An IP addressing scheme using ‘classes’ of IP addresses was
developed to make the task of subnetting networks easier. This
scheme is consistent and easy to deploy, but is wasteful of IP
address space. A new scheme was introduced called Classless
Interdomain Routing (CIDR), as an extension of the classed
addressing scheme. CIDR allows greater control over the number
of IP addresses assigned to a subnet.
The classed IP addressing scheme will be discussed first.
IP addresses used within an intranetwork (within a company
network, for instance) have two parts – a network part and a node
part. The classed addressing scheme provides a method of
determining the information necessary to forward packets to and
from the subnetwork.
The classed scheme defines 5 address classes. The first 4 bits in
the IP address determine which class the IP address falls in.
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Class A addresses begin with 0xxx, or 1 to 126 decimal.
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Class B addresses begin with 10xx, or 128 to 191 decimal.
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Class C addresses begin with 110x, or 192 to 223 decimal.
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Class D addresses begin with 1110, or 224 to 239 decimal.
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Class E addresses begin with 1111, or 240 to 254 decimal.
Addresses beginning with 01111111, or 127 decimal, are reserved
for loopback and internal testing on a local machine. (The address
127.0.0.1 always points loops back to the local computer – so you
can always ping this address, if the network is working). Class D
addresses are reserved for multicasting. Class E Addresses are
reserved for future use.