1 26-aug-15 addressing the network using ipv4 lecture # 2 engr. orland g. basas prepared by: engr....

19 Apr 2023 1

Addressing the network using IPv4

Lecture # 2Lecture # 2

Prepared by: Engr. Orland G. BasasEngr. Orland G. Basas

IT Lecturer

19 Apr 2023 2

IP addressing – works at

OSI model layer 3 TCP/IP model Internet layer

Application

Presentation

Session

Transport

Network

Data link

Physical

Application

Transport

Internet

Network Access

TCP, UDP

IP

Ethernet, WAN technologies

HTTP, FTP, TFTP, SMTP etc

Segment

Packet

Frame

Bits

Data stream

19 Apr 2023 3

The 32-bit binary addresses used on the Internet are referred to as Internet Protocol (IP) addresses

Commonly written in dotted-decimal format – 192.168.10.1 When IP addresses are assigned to computers, some of the

bits on the left side of the 32-bit IP number represent a network.

The bits left over in the 32-bit IP address identify a particular computer on the network A computer is referred to as the host

The IP address of a computer consists of a network & a host part that represents a particular computer on a particular network

IP addressing

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In the early days of the Internet, IP addresses were allocated to organizations based on request rather than actual need.

When an organization received an IP network address, that address was associated with a “Class”, A, B, or C.

This is known as Classful IP Addressing The first octet of the address determined what class the

network belonged to and which bits were the network bits and which bits were the host bits.

It was not until 1992 when the IETF introduced CIDR (Classless Interdomain Routing), making the address class meaning less.

This is known as Classless IP Addressing. For now, all you need to know is that today’s networks are

classless, except for those networks that still use Classful routing protocols.

Classful IP Addressing

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IPv4 Address Classes

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Class A

Class B

Class C

Network Host Host Host

Network Network Host Host

Network Network Network Host

1st octet 2nd octet 3rd octet 4th octet

N = Network number assigned by Internet registry H = Host number assigned by administrator

Address Classes

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Class A addresses

Network Host Host Host

First octet is between 0 – 127, begins with 0

Number between 0 - 127

8 bits 8 bits 8 bits

With 24 bits available for hosts, there a 224 possible addresses. That’s 16,777,216 nodes!

There are 126 class A addresses. 0 and 127 have special meaning and are not used.

16,777,214 host addresses, one for network address and one for broadcast address.

Only large organizations such as the military, government agencies, universities, and large corporations have class A addresses.

For example ISPs have 24.0.0.0 and 63.0.0.0

19 Apr 2023 8

Class B addresses

Network Network Host Host



8 bits 8 bits

With 16 bits available for hosts, there a 216 possible addresses. That’s 65,536 nodes!

There are 16,384 (214) class B networks. 65,534 host addresses, one for network address and one for broadcast

address. Class B addresses are assigned to large organizations including corporations

(such as government agencies, and school districts).

19 Apr 2023 9

Class C addresses

Network Network Network Host



8 bits

With 8 bits available for hosts, there a 28 possible addresses. That’s 256 nodes!

There are 2,097,152 possible class C networks. 254 host addresses, one for network address and one for broadcast address. Usually assigned for small networks

19 Apr 2023 10

Class D Addresses A Class D address begins with binary 1110 in the first

octet. First octet range 224 to 239. Class D address can be used to represent a group of

hosts called a host group, or multicast group.

Class E Addresses First octet of an IP address begins with 1111 Class E addresses are reserved for experimental

purposes and should not be used for addressing hosts or multicast groups.

IPv4 Address Classes

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Types of Addresses

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Subnet Mask

To inform a computer how the 32-bit IP address has been split, a second 32-bit number called a subnetwork mask is used

This mask is a guide that indicates how the IP address should be interpreted by identifying how many of the bits are used to identify the network of the computer

The subnetwork mask sequentially fills in the 1s of the network portion.

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Class A IP Address Default Subnet Mask: 255.0.0.0 (/8)

Default Subnet Mask

Class B IP Address Default Subnet Mask: 255.255.0.0 (/16)

Class C IP Address Default Subnet Mask: 255.255.255.0 (/24)

19 Apr 2023 14

Network Prefix

How do we know how many bits represent the network portion and how many bits represent the host portion?

We use network prefix. The prefix length is the number of bits in the

address that gives us the network portion Ex: 172.16.4.0 /24, the /24 tells us that the first 24

bits are the network address. This leaves the remaining 8 bits, the last octet, as the host portion.

19 Apr 2023 15

IPv4 address

192. 168. 21. 17

11000000 10101000 00010101 00010001

octetoctet octet octet

network part host part

255. 255. 255. 0

11111111 11111111 11111111 00000000

Prefix /24 Subnet mask:

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Find the network address

192. 168. 21. 17

11000000 10101000 00010101 00010001

In a network address, all the host bits are 0.

192. 168. 21. 0

11000000 10101000 00010101 00000000

The router needs to do this for every packet.

19 Apr 2023 17

Logical AND

192. 168. 21. 17

11000000 10101000 00010101 00010001

255. 255. 255. 0

11111111 11111111 11111111 00000000

Do a logical AND at each position

192. 168. 21. 0

11000000 10101000 00010101 00000000

19 Apr 2023 18

Find the broadcast address

192. 168. 21. 17

11000000 10101000 00010101 00010001

In a broadcast address, all the host bits are 1.

192. 168. 21. 255

11000000 10101000 00010101 11111111

The broadcast is the last address in the network.

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Reminder: 3 types of address

Every network has: Network address – the first one Broadcast address – the last one Host addresses – everything in between

19 Apr 2023 20

Recall: Classful addressing

10. 17. 53. 60


A

172. 16. 38. 201


B

192. 168. 21. 17


C

19 Apr 2023 21

Classful addressing

Easy to work out but very wasteful. Routers and hosts still assume default subnet

masks by class Class A /8 255.0.0.0 Class B /16 255.255.0.0 Class C /24 255.255.255.0

19 Apr 2023 22

Classless addressing

Any suitable prefix can be used We (and devices) need to know what the

prefix is. More flexible, less wasteful.

19 Apr 2023 23

Classless addressing /16

172.16.0.0/16 mask 255.255.0.0 Broadcast address 172.16.255.255

Hosts 172.16.0.1 to 172.16.255.254 65534 host addresses

172. 16. 0. 0

10101100 00010000 00000000 00000000

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172. 16. 0. 0

10101100 00010000 00000000 00000000

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172. 16. 0. 0

10101100 00010000 00000000 00000000

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172. 16. 0. 0

10101100 00010000 00000000 00000000

19 Apr 2023 27




172. 16. 0. 0

10101100 00010000 00000000 00000000

19 Apr 2023 28

Calculating addresses

A host has IP address 192.168.1.70/24 What is the subnet mask? What is the network address? What is the broadcast address? What is the range of host addresses in the

network?

19 Apr 2023 29

192.168.1.70/24 – fill in the table

Last octet binary

Last octet decimal

Full

Host

Subnet mask

Network

Broadcast

First host

Last host

19 Apr 2023 30

192.168.1.70/24

Last octet binary

Last octet decimal

Full

Host 01000110 70 192.168.1.70

Subnet mask 00000000 0 255.255.255.0

Network 00000000 0 192.168.1.0

Broadcast 11111111 255 192.168.1.255

First host 00000001 1 192.168.1.1

Last host 11111110 254 192.168.1.254

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network?

19 Apr 2023 32

192.168.1.70/26 fill in the table

Last octet binary

Last octet decimal

Full

Host

Subnet mask

Network

Broadcast

First host

Last host

19 Apr 2023 33

192.168.1.70/26

Last octet binary

Last octet decimal

Full

Host 01000110 70 192.168.1.70

Subnet mask 11000000 192 255.255.255.192

Network 01000000 64 192.168.1.64

Broadcast 01111111 127 192.168.1.127

First host 01000001 65 192.168.1.65

Last host 01111110 126 192.168.1.126

19 Apr 2023 34



network?

19 Apr 2023 35

192.168.1.70/28 fill in the table

Last octet binary

Last octet decimal

Full

Host

Subnet mask

Network

Broadcast

First host

Last host

19 Apr 2023 36

192.168.1.70/28

Last octet binary

Last octet decimal

Full

Host 01000110 70 192.168.1.70

Subnet mask 11110000 240 255.255.255.240

Network 01000000 64 192.168.1.64

Broadcast 01001111 79 192.168.1.79

First host 01000001 65 192.168.1.65

Last host 01001110 78 192.168.1.78

19 Apr 2023 37

Unicast, Multicast, Broadcast

Unicast – a message addressed to one host Broadcast – a message addressed to all

hosts on a network. Uses network’s broadcast address or 255.255.255.255 locally

Multicast – a message addressed to a group of hosts. Uses an address starting 224 - 239

19 Apr 2023 38

Private IP addresses

Unrestricted use on private networks. Not routed across the Internet.

10.0.0.0 – 10.255.255.255 (10.0.0.0/8) 172.16.0.0 – 172.31.255.255 (172.16.0.0/20) 192.168.0.0 – 192.168.255.255

(192.168.0.0/24)

19 Apr 2023 39

Public IP addresses

Routed over the Internet Master holder is IANA (Internet Assigned

Numbers Authority) Assigned to regional registries and then to

ISPs ISPs allocate them to organisations and

individual users Use is strictly controlled as duplicate

addresses are not allowed

19 Apr 2023 40

Special addresses

0.0.0.0 “all addresses” in default route. Hosts cannot be given addresses starting 0.

127.0.0.1 is loopback. Hosts cannot be given addresses starting 127.

240.0.0.0 and higher – reserved for experimental purposes.

169.254.0.0 - 169.254.255.255 local only 192.0.2.0 to 192.0.2.255 for teaching

19 Apr 2023 41

Network address translation

A large number of hosts on a network use private addresses to communicate with each other.

The ISP allocates one or a few public addresses.

NAT allows the hosts to share the public addresses when they want to use the Internet

19 Apr 2023 42

Addressing hosts

Static addressing – address is configured by an administrator

Servers, printers, routers, switches need static addresses

Dynamic addressing – address is allocated automatically by DHCP by leasing addresses from a pool

Dynamic addressing is best for workstations

19 Apr 2023 43

Subnetting 192.168.1.0/24

Address 192.168.1.0 00000000

Subnet mask 255.255.255.0 00000000

Last octet binary

Borrow 1 bit from host part, give it to network part, /25

Addresses 192.168.1.0192.168.1.128

0000000010000000

Subnet mask 255.255.255.128 10000000

19 Apr 2023 44


Borrow 2 bits from host part, give to network part, /26

Addresses 192.168.1.0192.168.1.64192.168.1.128192.168.1.192

00000000010000001000000011000000

Subnet mask 255.255.255.192 11000000

19 Apr 2023 45



Addresses 192.168.1.0192.168.1.32192.168.1.64192.168.1.96192.168.1.128 192.168.1.160 192.168.1.192 192.168.1.224

0000000000100000010000000110000010000000101000001100000011100000

Subnet mask 255.255.255.224 11100000

19 Apr 2023 46



192.168.1.0192.168.1.16192.168.1.32192.168.1.48192.168.1.64192.168.1.80192.168.1.96192.168.1.112

192.168.1.128192.168.1.144192.168.1.160192.168.1.176 192.168.1.192192.168.1.208192.168.1.224192.168.1.240

0000000000010000001000000011000001000000010100000110000001110000

1000000010010000 1010000010110000 1100000011010000 1110000011110000

Subnet mask 255.255.255.240 11110000

And so on…

19 Apr 2023 47


Every time you borrow another bit you: Double the number of subnets Halve the size of the subnets

Each subnet has a network address, a broadcast address, and everything in between is a host address.

Here are some ways of visualising the process.

19 Apr 2023 48


Bits borrowed 1 2 3 4 5 6

No of networks 2 4 8 16 32 64

Prefix /25 /26 /27 /28 /29 /30

Bit value/ network size

128 64 32 16 8 4

No of hosts 126 62 30 14 6 2

Subnet mask 128 192 224 240 248 252

19 Apr 2023 49

Ping and traceroute

Ping sends an ICMP message. If all is well, the destination replies. If not, a router may reply to say the destination is unreachable, or the ping may time out.

Traceroute sends a series of messages so that each router along the path replies. You get a list of addresses of all the routers.

19 Apr 2023 50

IPv6

Development started in 1990s because of concerns about IPv4 addresses running out

A whole new protocol suite – not just layer 3 Uses 128-bit hierarchical addressing, written

using hexadecimal Simpler header Integrated security – authentication, privacy Quality of service mechanisms

19 Apr 2023 51

Why Subnet?

To break the network down into pieces, each of which can be addressed separately. Controls network traffic Reduces broadcasts Can provide low level security with access lists on

the router Organization of IP address space

19 Apr 2023 52

Subnetting a Default Class C Network Address: 200.129.41.0

Default Class C address is divided into network and host portions as follows:

N . N . N . H To subnet we “borrow” bits from the host portion of the

address (8 bits for Class C)

N . N . N . x x x x x x x x Borrowing n bits yields 2n – 2 subnets. Leaving n bits yields 2n – 2 hosts. For a class C, we can borrow from 2 to 6 bits. Why not 1 bit? (How many usable subnets?) Why not 7 bits? (How many usable hosts?)

19 Apr 2023 53


Suppose we need 14 usable subnets, how many bits do we borrow? Remember, borrowing n bits give us:

2n – 2 subnets Try borrowing 3 bits (n = 3):

23 – 2 = 8 – 2

= 6 usable subnets (not enough) Try borrowing 4 bits

24 – 2 = 16 – 2

= 14 usable subnets (enough)

19 Apr 2023 54


Write it with the network octet in binary:

200.129.41.0000 0000

Borrowing 4 bits yields 14 usable subnets How many usable hosts per subnet?

Same formula as subnets (2n – 2) 4 host bits (n = 4) 24 – 2 = 16 – 2

= 14 usable hosts per subnet

subnet bits host bits

Break here

19 Apr 2023 55


Examples: First usable 200.129.41.0001 ^ 0000

subnet address: 200.129.41.16 First usable host 200.129.41.0001 ^ 0001

on the first subnet: 200.129.41.17 Second usable host 200.129.41.0001 ^ 0010

on the first subnet: 200.129.41.18.

.

.

Last usable host 200.129.41.0001 ^ 1110

on the first subnet: 200.129.41.30 Broadcast address 200.129.41.0001 ^ 1111

for the first subnet: 200.129.41.31

19 Apr 2023 56


Examples: Second usable 200.129.41.0010 ^ 0000

subnet address: 200.129.41.32 Third usable 200.129.41.0011 ^ 0000

subnet address: 200.129.41.48 Fourth usable 200.129.41.0100 ^ 0000

subnet address: 200.129.41.64

.

.

. Last usable 200.129.41.1110 ^ 0000

subnet address: 200.129.41.224

19 Apr 2023 57

The Subnet Mask: How the Router Determines the Subnet

The subnet mask (in binary) has: all ones in the network and subnet portion of the

address all zeros in the host potion of the address The subnet mask for the previous example is:

255.255.255. 240

255.255.255. 1111^ 0000 (128 + 64 + 32 + 16 =240) ANDing this mask with any valid host address on the

network will always yield the subnet address for that host.

19 Apr 2023 58

The Subnet Mask: How the Router Determines the Subnet

Example (our subnet mask is 255.255.255.240)

IP host address: 200.129. 41.23

Last octet to binary: 200.129. 41.0001 0111

AND subnet mask: 255.255.255.1111 0000

200.129. 41.0001 0000

Subnet Address: 200.129. 41.16

So the host address 200.129. 41.23 is on the 200.129.41.16 subnet.

19 Apr 2023 59

Subnetting a Default Class B Network Address: 132.178.0.0

Default Class B address is divided into network and host portions as follows:

N . N . H . H To subnet we “borrow” bits from the host

portion of the address (16 bits for Class B)

N . N . x x x x x x x x . x x x x x x x x For a class B, we can borrow from 2 to 14 bits.

19 Apr 2023 60


Suppose we need 80 usable subnets, how many bits do we borrow? Remember, borrowing n bits give us:

2n – 2 subnets Try borrowing 6 bits (n = 6):

26 – 2 = 64 – 2

= 62 usable subnets (not enough) Try borrowing 7 bits

27 – 2 = 128 – 2

= 126 usable subnets (enough)

19 Apr 2023 61


Write it with the network octets in binary:

132.178.0000000 0.00000000

Borrowing 7 bits yields 126 usable subnets How many usable hosts per subnet?

Same formula as subnets (2n – 2) 9 host bits (n = 9) 29 – 2 = 512 – 2

= 510 usable hosts per subnet

subnet bits host bits

19 Apr 2023 62


Examples: First usable 132.178.0000001 ^ 0.00000000

subnet address: 132.178.2.0 First usable host 132.178.0000001 ^ 0.00000001

on the first subnet: 132.178.2.1 Second usable host 132.178.0000001 ^ 0.00000010

on the first subnet: 132.178.2.2 . . .

Last usable host 132.178.0000001 ^ 1.11111110on the first subnet: 132.178.3.254

Broadcast address 132.178.0000001 ^ 1.11111111 for the first subnet: 132.178.3.255

19 Apr 2023 63


Examples: Second usable 132.178.0000010 ^ 0.00000000

subnet address: 132.178.4.0 Third usable 132.178.0000011 ^ 0.00000000

subnet address: 132.178.6.0 . . .

Ninety-first usable 132.178.1011011 ^ 0.00000000subnet address: 132.178.182.0

. . .

Last usable 132.178.1111110 ^ 0.00000000subnet address: 132.178.252.0

19 Apr 2023 64


The subnet mask for this example is:255.255.254.0

255.255.1111111 ^ 0.00000000

ANDing this mask with any valid host address on this network will always yield the subnet address.

19 Apr 2023 65


Example:IP host address: 132.178.119.112

Last octets to binary: 132.178.0111011 ^ 1.01110000

AND subnet mask: 255.255.1111111 ^ 0.00000000

132.178.0111011 ^ 0.00000000

Subnet Address: 132.178.118.0

Which subnet is this. How can you tell?

19 Apr 2023 66

Additional Info on subnetting

19 Apr 2023 67

The End

1 26-aug-15 addressing the network using ipv4 lecture # 2 engr. orland g. basas prepared by: engr....

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