chapter 6 (cont.) ip addressing subnetting cidr · ip addressing – subnetting cidr 1 . ip...

Chapter 6 (Cont.)

IP ADDRESSING – Subnetting

CIDR

1

IP Addresses

An IP address is an address used to uniquely identify a

device on an IP network.

• It designates the specific location of a device on the network.

• IP addressing was designed to allow hosts on one network to

communicate with a host on a different network regardless of

the type of LANs the hosts are participating in.

The address is made up of 32 binary bits which can be

divisible into a network portion and host portion with the help

of a subnet mask.

32 binary bits are broken into four octets (1 octet = 8 bits)

Dotted decimal format (for example, 172.16.81.100)

2

Network Addressing

3

Subdividing an IP address into a network and node address

is determined by the class designation of one’s network. This

figure summarizes the three classes of networks

3

IP Address Classes

4

IP Address Classes

• Class A: The first octet is the network portion. Octets 2, 3,

and 4 are for subnets/hosts

• Class B: The first two octets are the network portion. Octets 3

and 4 are for subnets/hosts

• Class C: The first three octets are the network portion. Octet 4

is for subnets/hosts

5

Private Address Range

Address Class Reserved Address Space

Class A 10.0.0.0 - 10.255.255.255

Class B 172.16.0.0 - 172.31.255.255

Class C 192.168.0.0 - 192.168.255.255

6

IP Terminology

7

BIT: A bit is one digit, either a 1 or a 0.

BYTE: A byte is 7 or 8 bits, depending on whether parity is used. For

the rest of this chapter, always assume a byte is 8 bits.

OCTET: An octet, made up of 8 bits, is just an ordinary 8-bit binary

number. In this chapter, the terms byte and octet are completely

interchangeable.

Network address: This is the designation used in routing to send

packets to a remote network—for example, 10.0.0.0, 172.16.0.0, and

192.168.10.0.

Broadcast address: The address used by applications and hosts to

send information to all nodes on a network is called the broadcast

address. 7

Reserved Addressing

8

Address Function

Network address of all 0s Interpreted to mean “this network or segment.”

Network address of all 1s Interpreted to mean “all networks.”

Network 127.0.0.1 Reserved for loopback tests.

Node address of all 0s Interpreted to mean “network address” or

any host on specified network.

Node address of all 1s Interpreted to mean “all nodes” on the

specified network

Entire IP address set to all 0s Used by Cisco routers to designate the

default route. Could also mean “any network.”

Entire IP address set to all 1s (same as Broadcast to all nodes on the

current network; 255.255.255.255)

sometimes called an “all 1s broadcast” or limited broadcast

8

Private Addressing

9

Address Class Reserved Address Space

Class A 10.0.0.0 through 10.255.255.255

Class B 172.16.0.0 through 172.31.255.255

Class C 192.168.0.0 through 192.168.255.255

9

Network Masks

• Distinguishes which portion of the address identifies

the network and which portion of the address

identifies the node.

• Default masks:

Class A: 255.0.0.0

Class B: 255.255.0.0

Class C: 255.255.255.0

10

Subnetting

Subnetting is a technique used to break down (or partition)

networks into subnets. The subnets are created through the

use of subnet masks.

Creates multiple logical networks that exist within a single

Class A, B, or C network.

If you do not subnet, you will only be able to use one network

from your Class A, B, or C network, which is unrealistic

Each data link on a network must have a unique network ID,

with every node on that link being a member of the same

network

11

The subnets are created by borrowing bits from the host portion of the IP address as shown.

The network portion of the IP address and the new subnet bits are used to define the new subnet. Routers use this information to properly forward data packets to the proper subnet.

12

The Class C network, shown is partitioned into four subnets. It takes 2 bits to provide four possible subnets therefore 2-bits are borrowed from the host bits.

This means the process of creating the four subnets reduces the number of bits available for host IP addresses.

13

Benefits of Subnetting

1) Reduced network traffic

2) Optimized network performance

3) Simplified management

4) Facilitated spanning of large geographical distances

15

How to create subnets

Determine the number of required network IDs:

One for each subnet

One for each wide area network connection

Determine the number of required host IDs per subnet:

One for each TCP/IP host

One for each router interface

Based on the above requirements, create the following:

One subnet mask for your entire network

A unique subnet ID for each physical segment

A range of host IDs for each subnet

16

No Subnetting

• All hosts think that the other hosts are on the same network

128.143.0.0/16

128.143.137.32/16subnetmask: 255.255.0.0

128.143.71.21/16

subnetmask: 255.255.0.0

128.143.137.144/16


128.143.71.201/16subnetmask: 255.255.0.0

17

128.143.0.0/16

128.143.137.32/24


128.143.71.21/24


128.143.137.144/24


128.143.71.201/24


128.143.137.0/24

Subnet

128.143.71.0/24

Subnet

With Subnetting

• Hosts with same extended network prefix belong to the same

network

18

• Different subnetmasks lead to different views of the scope of

the network

128.143.0.0/16

128.143.137.32/26

subnetmask: 255.255.255.192

128.143.71.21/24


128.143.137.144/26

subnetmask: 255.255.255.192

128.143.71.201/16


128.143.71.0/24

Subnet128.143.137.128/26

Subnet

128.143.137.0/26

Subnet

With Subnetting

19

Subnetting

• Scenario: Organization has

a large network prefix and

wants to create smaller

networks.

• Subnetting: Use a portion

of the host name to identify

a smaller network

(“subnetwork”, “subnet”).

• Each subnet becomes a separate

network

UofT Network

Faculty of A&S

Library

Faculty of

Engineering

128.100.0.0/16

128.100.11.0/24 128.100.58.0/24

128.100.136.0/24

20

Subnetting Basics

• Benefits of subnetting include:

– Reduced network traffic

– Optimized network performance

– Simplified management

– Facilitated spanning of large geographical distances.

21

Advantages of Subnetting

• With subnetting, IP addresses use a 3-layer hierarchy:

» Network

» Subnet

» Host

• Reduces router complexity. Since external routers do not

need to know about subnetting, the complexity of routing

tables at external routers is reduced.

• Flexibility: Length of the subnet mask need not be identical on

all subnetworks.

22

How To Create Subnets

Take bits from the host portion of the IP address and

reserve the to divine the subnet address.

23

Understanding the Powers of 2

24

Subnet Masks

• Used to define which part of the host address will be used

as the subnet address.

• A 32-bit value that allows the recipient of IP packets to

distinguish the network ID portion of the IP address from

the host ID portion.

25

Subnetting

and

Supernetting

26

• IP address consists of a network prefix and a host number

• Prefix notation: 128.100.__.__/16

• Notation with netmask: 128.100.__.__

255.255.0.0

Network Prefix and Host number

255 0 0

128.100

network prefix host number

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

255

netmask

27

• IP address consists of a network prefix and a host number

• Prefix notation: 128.100.__.__/__

• Notation with netmask: 128.100.__.__

255.255.__.__

Actual Network Prefix

255 0 0

128.100


1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

255

netmask

28

Basic Idea of Subnetting

• Split the host number portion of an IP address into a subnet number and a (smaller) host number.

• Result is a 3-layer hierarchy

• Then: • Subnets can be freely assigned within the organization

• Internally, subnets are treated as separate networks

• Subnet structure is not visible outside the organization


subnet number network prefix host number

extended network prefix

29

• Start of the host number is indicated by prefix or netmask notation

• The netmask of the extended network prefix is called subnetmask (and

the nework is called subnet)

Subnetmask

128.100 11.60


128.100 60

network prefix host number subnet

number

11

extended network prefix

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0

subnetmask

30

chapter 6 (cont.) ip addressing subnetting cidr · ip addressing – subnetting cidr 1 . ip...

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