Understanding the
TCP/IP Internet
Layer
Building a Simple Network
© 2007 Cisco Systems, Inc. All rights reserved. ICND1 v1.0—1-1
Internet Protocol Characteristics
Operates at network layer of OSI
Connectionless protocol
Packets treated independently
Hierarchical addressing
Best-effort delivery
No data-recovery features
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Why IP Addresses?
They uniquely identify each device on an IP network.
Every host (computer, networking device, peripheral) must have
a unique address.
Host ID:
– Identifies the individual host
– Is assigned by organizations to individual devices
Network.Host
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IP PDU Header
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IP Address Format: Dotted Decimal
Notation
The binary-to-decimal and decimal-to-
binary conversion will be detailed later
in this course.
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IP Address Classes: The First Octet
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IP Address Ranges
*127 (01111111) is a Class A address reserved for loopback testing and cannot
be assigned to a network.
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Reserved Address
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Public IP Addresses
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Private IP Addresses
Class Private Address Range
A 10.0.0.0 to 10.255.255.255
B 172.16.0.0 to 172.31.255.255
C 192.168.0.0 to 192.168.255
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DHCP
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DNS
Application specified in the TCP/IP suite
A way to translate human-readable names into IP addresses
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Network Connection
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ipconfig
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Summary
IP network addresses consist of two parts: the network ID and the
host ID.
IPv4 addresses have 32 bits that are divided into octets and are
generally shown in dotted decimal form (for example,
192.168.54.18).
When written in a binary format, the first bit of a Class A address
is always 0, the first 2 bits of a Class B address are always 10,
and the first 3 bits of a Class C address are
always 110.
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Summary (Cont.)
Certain IP addresses (network and broadcast) are reserved and
cannot be assigned to individual network devices.
Internet hosts require a unique, public IP address, but private
hosts can have any valid private address that is unique within the
private network.
DHCP is used to assign IP addresses automatically, and also to
set TCP/IP stack configuration parameters such as the subnet
mask, default router, and DNS servers.
DNS is an application that is specified in the TCP/IP suite,
providing a means to translate human-readable names into IP
addresses.
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Summary (Cont.)
Host provides tools that can be used to verify the IP address of
the host:
– Network connections
– IPCONFIG
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