constructing network addresses © 2004 cisco systems, inc. all rights reserved. classifying network...

Constructing Network Addresses

© 2004 Cisco Systems, Inc. All rights reserved.

Classifying Network Addressing

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—5-2

Outline

• Overview

• IP Addressing

• IP Address Structure

• IP Address Classes

• Reserved IP Addresses

• Public and Private IP Addresses

• IPv4 vs. IPv6

• Summary

• Quiz


Network and Host Addresses

IP Address is a hierarchical address and consists of 2 parts:

Network address portion (Network ID)

Host address component (Host ID)


Dotted Decimal Notation

• IP address is a hierarchical address and consist of 2 parts:

• >Network address portion (network ID)

• >Host address component (host ID)

• An IP address is a 32-bit binary number:10101100000100001000000000010001

• The 32-bit binary number can be divided into four octets:10101100 00010000 10000000 00010001

• Each octet (or byte) can be represented in decimal:172 16 128 17

• The address can be written in dotted-decimal notation:172.16.128.17

• The 32-bits number represents the network and the remaining bits represent the host.


IP Address Classes

*Class D addresses are used for multicast groups. There is no need to allocate octets or bits to separate network and host addresses.

**Class E addresses are reserved for research use only.


IP Address Class Components

• N = Network number assigned by ARIN

• H = Host number assigned by administrator


IP Address Range

Class A Extremely large network, 16,777.000 available host address.

Class B Large network, 16,384 networks,each supporting more then 65,000 hosts.

Class C small networks, more than 2 million networks,each supporting up to 256 host.

*127 (011111111) is a Class A address reserved for loopback testing and cannot be assigned to a network. (127.0.0.1)


Network Addresses


Broadcast Address


Public IP Addresses


Private IP Addresses

When a network using private address must connect to the Internet, it is necessary to translate the private address to a public addresses. This translation process is called NAT. A router is often the network device that perform NAT.


IPv4 Address Allocation


IPv4 and IPv6

8*4=32 bits

8*16=128 bits


Summary

• IP network addresses consist of two parts: the network portion and the host portion.

• IPv4 addresses have 32 bits that are divided into octets and are generally shown in dotted decimal form (for example, 192.168.54.18).

• IPv4 addresses are divided primarily into A, B, and C classes. Other classes (D and E) exist, but they are reserved for special uses (multicasting and research).

• 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.


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.

• Addressing space as defined by IPv4 is limited and has been mostly exhausted.

• The more flexible IPv6 will replace IPv4 in the future. IPv6 offers 128 bits of addressing compared to the 32-bit addressing available in IPv4.

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