Chapter
IP Addressing Format
© N. Ganesan, All rights reserved.
Questions
• How many bits are there in a TCP/IP address?
• Name the components of a typical TCP/IP address?
• What is the difference between the old IPv4 and the
new IPv6 addresses?
• Explain the difference between network ID and host
ID.
• Name the classes of IP addresses. What are the
purpose and function of each class of addressing
• Compute the number of networks and hosts that can
be supported in each class of address.
Questions Cont.
• List the restrictions placed on the
assignment of addresses.
• Choose an IP class as an example and
list the valid range of network and host
addresses for that class.
Chapter Modules
• IP Address Format and Components
• Classes of Addresses
• Scope of Addresses and Restrictions
Module 1
IP Address Format
© N. Ganesan, All rights reserved.
Overview
• The IP address format discussed in this
presentation applies to IPv4
• An IP address is composed of 32 bits
that is viewed as being divided into 4
octets
– One octet is made up of 8 bits
IP Address Format
32 bits divided into 4 octets for convenience
10101111
11001100
10000001
00110011
175
204
129
51
Converted into decimals for easy
representation and remembrance
An Example in Binary-toDecimal Conversion
Binary
1
0
0
1
Factor
8
4
2
1
Decimal=
Binary * Factor
8
0
0
1
Binary 1001 = Decimal 9
8+1
=9
IP Addressing Components
32 bits
Network ID
Host ID
The New IP Address
• The new IP address known as IPv6 has
128 bits
– www.whatis.com
IP Component Reference
Network ID
Host ID
Internet
Host ID
End of Module
Module
Classes of IP Addresses
© N. Ganesan, All rights reserved.
Classes of IP Addresses
• IP addresses have been divided into
classes
– They are namely Classes A, B C, D and E
• Classes A, B and C are used for
commercial purpose
• Class D is used for multicasting
• Class E is used for experimental
purpose
Commercial Classes
• Classes A, B and C
• Class A is for very large organizations
– Few, if any, are available
• Class B is used in medium size organizations
– A few may be still be available
• Class C is used in small organizations
– Often further divided and issued to smaller
organizations and individuals
Subnetting
• There is no strict rule as to who may
use a certain class of address
• An enterprise such as an ISP can own a
large Class B address space and subnet
it into smaller spaces for its customers
Class D
• Reserved for IP multicasting
• The first four higher-order bits are set to
1 1 1 0 respectively
• Microsoft supports Class D addresses
for multicasting
• Multicasting is the process of delivering
media over the Internet at reduced
bandwidths
A Note on Multicasting
• Multicasting delivers a single stream of
medial to a router and the receiving end
• The router then multiplies and delivers the
stream to local clients
• As such, only one stream travels along the
Internet thus saving bandwidth
• In the case of Unicasting, multiple streams
travel along the Internet to reach each client
separately
Unicasting
3 Streams
Multicasting
1 Stream on
Internet
3 Streams Locally
Broadcasting
• One stream is sent to the destination
• The stream is then multiplied and sent
to the hosts regardless of the fact that
the hosts do or do not request to receive
the broadcast
Alternative Methods of Delivering
Media
• Unicasting
– Easy to implement
– Higher bandwidth is required for transmission
• Multicasting
– More involved in setting up
– Uses bandwidth more efficiently
• Broadcasting
– More involved in setting up
– Uses bandwidth more efficiently from host to the local
router
– However, the bandwidth usage within the local network
may be higher
Class E
• Experimental addresses reserved for
possible future use
• The first four higher-order bits are set to
1 1 1 1 respectively
End of Module
Module
IP Formats for Commercial
Classes
© N. Ganesan, All rights reserved.
Class A Assignment Format
Network ID (8 bits)
8 bits
8 bits
8 bits
Host ID (24 bits)
8 bits
Number of Class A Networks
and Nodes
• The first higher-order bit is always set
to 0
• Total number of networks supported is
126 = 27 - 2
– All zeros and all ones are not allowed
• Total number of hosts supported per
network is 16,777,214 = 224 - 2
– All zeros and all ones are not allowed
Restrictions on Zeros and Ones
• The initial RFC 950 forbade the use of
zeros and ones
– All zeros prevented some early routing
protocols from operating correctly
– All ones may result in a conflict with a
special broadcast address known as the allsubnets directional broadcast address
Easing of Restrictions
• RFC 1812 now eases the restriction and
allows the use of zeros and ones in a
CIDR-compliant environment
• CIDR
– Classless Inter-Domain Routing (CIDR)
– Explained under subnets
Class B Assignment Format
Network ID (16 bits)
8 bits
8 bits
8 bits
8 bits
Host ID (16 bits)
Number of Class B Networks and
Nodes
• The first two higher-order bits are
always set to 1 and 0 respectively
• Total number of networks supported is
16384 = 214 - 2
– All zeros and all ones are not allowed
• Number of hosts supported per
network is 65,534 = 216 - 2
– All zeros and all ones are not allowed
Class C Assignment Format
Network ID (24 bits)
8 bits
8 bits
8 bits
8 bits
Host ID (8 bits)
Number of Class C Networks and
Nodes
• The first three higher order bits are
always set to 1, 1 and 0 respectively
• Total number of networks supported is
2,097,152 = 221 - 2
– All zeros and all ones are not allowed
• Number of hosts supported per
network is 254 = 28 - 2
– All zeros and all ones are not allowed
Overcoming the Limited Number
of IP Addresses
• By dynamically assigning IP addresses to the
clients
– DHCP
– DHCP is also used for better management of
network
• Network Address Translation (NAT)
– Assign fictitious IP addresses to the clients
– Often, implemented with hardware firewalls
– NAT provides security as well
Increasing IP Address Space
• IPv6 would increase the address space
as it is 128 bits long whereas IPv4 is
only 32 bits long
End of Module
Module
Scope and Restriction of IP
Addresses
© N. Ganesan, All rights reserved.
Restrictions on Network ID
Assignments
• In class A, network ID 127 is reserved for
loop back functions
• All bits of a network ID cannot be set to ones
– Reserved for use as an IP broadcast address
• All bits of a network ID cannot be set to zeros
– Reserved for a specific host on the local host
– Packets destined to this specific address will not
be routed
Loop Back Function
• Loop back function simply tests itself
– Eg: 127.0.0.1 performs a test on the
machine itself
• localhost is another way of testing the
loopback function
Valid Network IDs for Classes
Class
Beginning
Network
ID
Ending
Network
ID
A
1.0.0.0
126.0.0.0
B
128.0.0.0
191.255.0.0
C
192.0.0.0
223.255.255.0
Restrictions on Host ID
Assignments
• All the bits of a host ID cannot be set to
ones
– Reserved as the broadcast IP address to
send a packet to all the hosts
• All the bits of a host ID cannot be set to
zeros either
– Reserved to represent the IP network
address
Valid Host IDs for Classes
Class
Beginning
Host ID
Ending Host ID
A
w.0.0.1
w.255.255.254
B
w.x.0.1
w.x.255.254
C
w.x.y.1
w.x.y.254
Summary of Networks and Hosts
Supported in Each Class
A
Network Available Hosts per
ID Portion Networks Networks
126
16,777,214
B
16,384
65,534
C
2,097,152
254
End of Module
Module
Private IP Addresses
© N. Ganesan, All rights reserved.
Private IP Addresses
• Addresses that cannot be accessed from the
Internet
• An important application is in setting up
firewalls
– IP addresses are used for clients on the user side
of the network
• May also be used in setting up local networks
that do not need access to the Internet
Firewall IP
Configuration
• What are private IP addresses?
– The Internet Assigned Numbers Authority (IANA) has
reserved the following three blocks of the IP address space
for private internets (local networks):
– 10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255
• Also, IP addresses in the range of 169.254.0.0 169.254.255.255 are reserved for Automatic Private IP
Addressing.
• Source: http://www.duxcw.com/faq/network/privip.htm
Private IP Addresses
End of Module
END OF MODULE
END OF CHAPTER