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An Internet Protocol address (IP address) is a numerical label assigned to each device connected to 3

the computer network that uses the Internet protocol for communication an IP address serves two principal 4

functions: host or network interface identification and location addressing. Internet Protocol version 4 (IPv4) defines an IP address as a 5

32-bit number.[ 6

However, because of the growth of the Internet and the depletion of available IPv4 addresses, 7

a new version of IP (IPv6), using 128 bits for the IP address. 8

When the PDU named segment reaches the Network Layer, this layer adds the IPv4 or IPv6 headers 9

to the segment and PDU name is converted to «Packet» in network layer. 10

And let's take a look to IP version 4 header now. 11

And as you can see that there are lots of fields in IP v4 version header and they are 12

version field, 13

They are type of service fields, header length field, total length field , fragment offset, protocol, TTL 14

header checksum, source and destination IP addresses and IP option. 15

Please keep in mind that there are lots of fields in here as you can see. 16

lets take a look to ipv4 limitations. 17

As we talked in our first slide of our course, almost 50 billion devices will be connected to internet 18

by 2020. 19

but however Available IPv4 addresses 20

are decreasing. In spite of IPv4 is still the most common used protocol, 21

it seems like our next step will be IPv6 which can provide a broad ip address range. 22

IPv6 provides a huge IP address range and more secure environment. With IPv4, we will not 23

Network Address Translation operation which converts 24

private ip addresses into public ip addresses. 25

And let's take a look to the differences between IPV 4 and IP version 6. 26

The first difference is address size. IPV 4 is thirty eight bit number while IP version 6 is one hundred 27

and twenty eight bit number. 28

The second is address format. IPV 4 is shown in decimal notation. 29

As you can see there are dots between the decimal numbers while IP version 6 is shown in hexadecimal 30

notation and there is a difference in the prefix notation as well. 31

And the biggest difference between these guys is really the number of the addresses that they are supporting. 32

As you can see there ipv4 is supporting this and Ip version 6 is supporting a really huge 33

number of IP addresses. 34

Let's take a look. 35

The IP version 6 header now. 36

Ipv6 header is pretty straight forward as you can see. on the screen there are 14 fields 37

in the IP version for header as you can see version I H-L type of service total length and et 38

but there are just 8 fields in ipv6 header and they are version, traffic class 39

flow label, payload length….. 40

Let's take a look to the routers. 41

Now. A router is a Layer 3 network gateway device, meaning that it connects two or more networks and 42

that the router operates at the network layer of the OSI model. 43

The main function of router is «ip routing» using the routing table entries. 44

If you remember from our previous slides, on the switches 45

there was a MACaddress table and switches we were making the switching by using the MAC address entries on 46

the Mac table. 47

But what rotuers are doing is, this is a router 48

this guy is keeping a routing table this time routing table which consists of IP Address entries, 49

and routers are making IP routing by using the IP address is kept in the routing table. 50

And here is backplane of a router as you can see there are some equipments in here, like on off switch 51

, like the input power connection, like the gigabit ethernet ports like usb ports and something like that 52

if you want to check routers' physical view, deeply there is a great application on Google 53

Play store and you can simply go the Google Play store and type Cisco 3D interactive 54

catalog and you can check the physical view of the routers deeply there. 55

.. 56

Let's take a look to the router memory now. 57

In router memory. 58

We have four types of memory. 59

The first one is RAM 60

The second is ROM. 61

And the other ones are NVRAM and the flash. In RAM 62

We are storing the running I O S, which is the operating system of the router and the running configuration 63

routing and ARP tables and packet buffers. in the ROM 64

We are storing the boot up instructions and limited Ios, in the NVRAM we are storing the sturtup config. 65

And in the flash we are storing the IOS itself and the other system files. 66

And please keep in mind that just ram is valotile. 67

So how a router boots up? 68

Let's take a look at this. 69

The first thing when router is booting up is POST: power on self tests. on this step. 70

The hardware is being checked. 71

Then ROM loads the bootstrap program and searches for the IOS which is the operating system of 72

the router . than iOS is being loaded from the flash and the startup configuration is loaded from the 73

NVRAM and in the last step, boot process is completed as everything is loaded into the ram. 74

Let's take a look through the routing process. 75

If source and destination have same network IDs, source sends the packet directly to the destination 76

That's a really important thing that you should keep on your mind. 77

But what is a Network ID? 78

(network ID) is a portion of the IP address that is used to identify individuals or devices on a network 79

such as a local area network or the Internet. On our later section 80

We'll see how we can calculate the network ID value as well. 81

But If source and destination have different network IDs from each other, source sends the packet to 82

A default gateway is the node in a computer network using the Internet 83

Protocol Suite that serves as the forwarding host (router) to other networks when no other route specification 84

matches the destination IP address of a packet. 85

For example in here PC one wants to communicate with the PC 4, they have different network IDs the 86

network id of PC one is .1 87

network ID of pc 4 is .20, 20 I'm going to show you how I calculate these numbers 88

later sections then because they have different network IDs, 89

If PC one wants to communicate with the PC 4 , this guy directly throws the packet to the default 90

gateway which is the internal interface IP address of this router on the middle. 91

But if PC one wants to communicate with the PC two and because they have the same network IDs, the packet 92

the packet is not forwarded to default gateway and that is directly forwarded to the PC two. 93

So let's take a look how we can configure an IP address for switches. 94

Now, if we want to communicate the default gateway on switch the command we're using is IP default-gateway 95

and the IP address of the router's internal interface. 96

And if you want to configure a default gateway for hosts, for example for this PC, if I want 97

to configure the default gateway, on the Internet Options There is a field showing us the default gateway 98

I can simply fill this here with the IP address of the default gw configure my host. 99

So the next thing we are going to focus on is the routing table. in computer networking routing table 100

is a data table stored in a router or a networked computer that lists the best paths to particular network 101

destinations. 102

and in some cases, metrics (distances) associated with those routes 103

The key term in here is the best path. 104

For example let's say that you want to go from London to Manchester. what you will do is you open the Google 105

Maps perhaps. 106

And London is here and Manchester is in here let's say. 107

And when you open the Google Maps you use the London to the From field and you enter the Manchester 108

to the destination field. 109

Then Google Maps shows you a few 110

Alternate paths how to how to get from London to Manchester. 111

But offers you one best path. 112

That's the fastest one. 113

So routing table is something like that too in the routing table You will always have the best path for the particular . 114

destination. 115

In here we're seeing an example of the routing table and we need to type "show ip route" simply to display 116

the routing table in here. 117

And as you can see in here for example that's a routing table entry which shows us the how we can reach 118

the 0.1 network , via1.6. 119

It's saying us then that's the best path. 120

And in here also we have another best path. 121

We have also routing tables on our PCs.And to see our PCs routing table, we can type "route print" on our command window. 122

So as I told you if I want to check the router's routing table, I'm typing "show ip route" command and 123

I'm seeing the best paths for the particular destinations. 124

So how I'm going to examine the routing table entries? 125

So in a routing table entry we have some text characters and some numbers as 126

you can see the first character is you're seeing on the routing table entry identifies how the network 127

was learned by the router. 128

For example if this route was learned by statically or learned by a dynamic routing protocol such as maybe 129

EIGRP, OSPF or something like that. 130

The second field identifies destination to the network. 131

Then this field identifies the administrative distance which is the thrustworthiness 132

of the route source . then this field identifies the metric to reach to the remote network and this 133

field identifies the next hop IP address to reach to the remote network. 134

And this field identifies the amount of elapsed time since the network was discovered and here identifies 135

the outgoing interface on the router to reach the destination network. 136

So let's take a look to router packet forwarding now. Routers 137

automatically know the directly connect to networks guys and remote networks must be learned by static routing 138

or dynamic routing protocols.For example if router one wants to communicate with router 2 what I'm gonna do is I'm going to go 139

to router zero and say this guy that hey dude if you want to communicate with this network for example 140

because this guy knows the directly connected interfaces automatically and this guy does not know anything 141

about in here, in here and in here and in here also. 142

So what I'm going to do is I'm going to go to this guy and I'm going to configure something saying that 143

hey router zero. 144

if you want to communicate with the network 2.0 send your packet to for example here 145

Or if you are to communicate with 3.0 send your packet to here. 146

I can manually configure this or use the dynamic routing protocol saying that if you want to go the 147

here use the EIGRP protocol, if you want to go here use the OSPF protocol or something like that. 148

I'm going to show you in much deeper on our later sections. 149

Again. 150

So let's take a look at the basic router configuration now. in a basic router configuration we can simply 151

configure hostname for example. 152

So let's say that we have a router named 153

My router, in the config mode. 154

I need to type host name command and I need to give a host name to our device and as soon as I type 155

the enter as you can see the host name changed to r0 156

And if I want to configure the interface, I need to go to the interface mode by typing interface and 157

the name of the interface which is fa 0/1 for this one. 158

And I am typing IP address and the IP address of the interface and the subnet mask of the interface. 159

All right guys if you could not understand what I'm telling about in here don't worry we are going 160

to make separate a wonderful packet tracer 161

Lab examples and you'll get 162

All of these concepts easily 163

Trust me. 164

So to verify the interface configuration the command I'm using. 165

This time is show IP interface brief and I can check the IP addresses attached to each interface 166

by using this command.