The OSI
reference model divides the application layer of the TCP/IP stack into three separate
layers.
Understanding TCP/IP??™s Internet Layer
Among the protocols included in the TCP/IP protocol stack are a network layer protocol
and a transport layer protocol. The internetworking layer handles the routing of packets of
data by using IP addresses to identify each device on the network. Each computer, router,
printer, or any other device attached to a network has its own unique IP address that routes
packets of data.
Each IP address has a speci?¬?c structure, and various classes of IP addresses exist. In
addition, subnetworks and subnet masks play a role in IP addressing schemes, and different
routing functions and protocols are involved in transmitting data from one network node to
another using IP addresses.
The various aspects of IP addressing include calculations for constructing an IP address,
classes of IP addresses designated for speci?¬?c routing purposes, and public versus private
44 Chapter 1: Building a Simple Network
IP addresses. Also, two different types of IP addresses exist: IP version 4 (IPv4) and
IP version 6 (IPv6). The 32-bit IPv4 address type is currently the most common, but the
128-bit IPv6 address is also in use and will probably become the more common address
type over time.
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