Addressing the Network – IPv4

Addressing the Network
– IPv4

Network Fundamentals – Chapter 6

ITE I Chapter 6

© 2006 Cisco Systems, Inc. All rights reserved.

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Objectives


Identify the structure IP addressing and demonstrate the ability
to convert between 8-bit binary and decimal numbers.



Identify an IPv4 address, classify by type and describe how it is
used in the network



Identify how addresses are assigned to networks by ISPs and
within networks by administrators



Identify the network portion of the host address and explain the
role of the subnet mask in dividing networks.



Given IPv4 addressing information and design criteria, calculate
the appropriate addressing components.



Identify common testing utilities to verify and test network
connectivity and operational status of the IP protocol stack on a
host.

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IP Addressing Dotted decimal Structure
 An IP address structure in dotted decimal form can be
seen by inspecting the TCP/IP properties of a PC as
below:

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IP Addressing Dotted Binary Structure
 Dotted decimal IP addresses can be expressed in dotted
binary form. Each octet is simply converted to its binary
equivalent

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8 bit Binary to decimal conversion
 1 Write down the 8 bit binary number
 2 Write down the decimal value above each bit
 3 Add only decimal values above a 1 bit (Ignore values above 0 bits)
 4 The total for all 8 bits is decimal number

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Decimal to Binary (using short division)

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Decimal to Binary (using short division)

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Decimal to 8- bit binary

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Network, Broadcast and host Addresses
An address can represent:
 The Network only (Network Address, Wire Address)
 All hosts i.e. PC’s, Servers, Printers, Router interfaces on the network (Broadcast
Address) e.g DHCP request, ARP request or Routing update (RIP)
 A single host on the network (Host Address)

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Example
 Determine the network, broadcast and host addresses
for a given address and prefix combination

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Example
 172.16.4.32/28 (28 Network bits 4 Host bits)
 Network address is 172.16.4.32
 Subnet mask is 255.255.255.240
 First Useable host address is 172.16.4.33
 Last Useable host address is 172.16.4.46
 Broadcast address is 172.16.4.47 i.e. all host bits are
set to 1

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Calculations (Convert both numbers to Binary)

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Calculations (Work out the range of numbers
in the host portion)

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Calculation (Add the host values to the
complete address)

Useable addresses = Total addresses – 2
= 24- 2 (where 4 is the number of bits in host portion)
= 16 - 2
= 14

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Address communication types
 Unicast – 1 to 1 communication
 Broadcast 1 to all network host communication
(Directed or Limited)
 Multicast 1 to a group of hosts on the network
communication

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IPv4 Addresses usage
 Address ranges reserved for special purposes in the
IPv4 protocol
Legacy Class A,B and
C Used for hosts
Multicast address used
for Routing Protocols
Exchange, Software
distribution, Audio and
Video Broadcasts

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Public and Private addresses
 Public addresses can move across the internet in
packets
 Private address must remain within a network

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Classes of IPv4 Addresses
 Packets with Private address (Link-Local and Test –
Net) are not routed on the internet

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Classify and Define IPv4 Addresses
 In the early 1980s IPv4 addresses were divided into
classes

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Assigning Addresses
 Addresses can be public or private and assigned
manually, automatically by server or automatically by
hosts operating systems in a peer to peer network

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Configuring Addresses
 TCP/IP setting allows to setting of IP addresses

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Assigning Addresses
 Network hardware can have IPv4 addresses also

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IANA, Regional agencies and ISPs
 Internet Assigned Number Authority (IANA), Internet
regional agencies and ISPs manage the allocation of IP
addresses to organisations
IANA manage addresses overall and the registries manage the addresses for
particular geographic regions

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ISPs and the Internet Backbone
 All ISPs are connected to the internet back. Tier1
directly, Tier 2 through Tier 1 and Tier 3 through Tier 2
 The bigger the company the closer it is to the back
bone

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The subnet mask can be used to find the
network for an IP address
To calculate the network address of a given
IP address the logic ANDing of any 2 bit
values must be understood
AND Truth table for two bit values

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Logically AND each bit in the IP address with
its subnet mask bit, the result is the network
bit

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Another Example

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Subnetting a Network address
 Subnetting is the process of borrowing bits from the left hand
side of the host portion of the address and subnet mask and
reassigning them as network bits, in order to create smaller
subnets within a network address. Networks can be subnetted
on the basis of subnets required or hosts per subnet

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Subnetting use a table

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Subnetting a Network address
 Extend the subnet mask to divide a network into
smaller networks

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Subnetting Starting point
To begin we have the address 192.168.1.0/24.This gives
us 1 network of 28 = (256 – 2) = 254 useable hosts

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Subnetting – decide the network needs
 The network requires 2 separate networks for each router interface
 We therefore borrow 1 bit from the host portion of the subnet mask
changing it from /24 to /25
 Borrowing 1 bit gives 21 = 2 networks

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Subnetting- look at the host portion
 The new host portion is now 7 bits wide. This give us 2 1 = 2 networks each of
 27=128 – 2= 126 useable hosts
 The addresses for each subnet can be determined by the decimal weighted value of the
last subnet mask network bit

This bit has been borrowed
from the host portion and
converted to a network bit
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Subnetting – examine the octet
 Each octet in an IP address and subnet mask have bits worth:
128 64 32 16 8 4 2 1
1
Octet of subnet mask)

0

0

0 0 0 0 0 (4th

 In the example we can see that the decimal weighted value is 128.
 This means that our subnet addresses will increase in steps of 128
hosts
 This gives the 2 subnet addresses of: (Note 2 subnets because 1 bit was
borrowed i.e. 21 =2 subnets
192.168.1.0/25
192.168.1.128/25

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Subnetting work out the host portion

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Subnetting- calculate the addresses in each
subnet
 The host addresses on each subnet are calculated as
before:
 For 1st subnet 192.168.1.0 =(Network + all host bits are
zeroes)
 192.168.1.1=(Network + First useable value in host
portion)
 192.168.1.126 =(Network + Last useable value in host
portion)
 192.168.1.127 (BC) =(Network + all host bits are ones)

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Subnetting- calculate the addresses in each
subnet

 For 2nd subnet 192.168.1.128 =(Network + all host
bits are zeroes)
 192.168.1.129=(Network + First useable value in
host portion)
 192.168.1.254 =(Network + Last useable value in
host portion)
 192.168.1.255 (BC) =(Network + all host bits are
ones)

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IPv6 protocol
 Improve packet handling via simplified header,
scalability via 128 bit addressing scheme, QOS via
Flow labeling and integrated security

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Summary
 IP addresses are hierarchical (have structure) with a network, host and
sometimes a subnet portion.
 All IPv4 addresses can represent a complete network, a specific host, a
group of hosts or broadcast address of the network
 Addressing authorities and ISPs allocate address ranges to companies.
Companies can then divide the address ranges into subnets by extending
the subnet mask and reassigning host bits to network bits
 Networks can be subnetted on the basis of subnets required or hosts per
subnet or both
 If networks are being subnetted based on hosts required. Always start with
the largest host requirement
 Planning makes the best use of the addressing scheme
 IP network addresses can be tested by using Ping and Tracert
 IPv6 is a new layer 3 protocol with new protocols at various layers to
support it
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Labs
 IPv4 Address Subnetting Part 1
Network address
Network broadcast address
Total number of host
Number of hosts

 IPv4 Address Subnetting Part 2
The subnet address of a subnet
The broadcast address of a subnet
The range of host addresses for a subnet
The maximum number of subnets for a subnet mask
The number of hosts for each subnet
The number of subnet bits
The number of a subnet

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Addressing the Network – IPv4

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