All language subtitles for 5. Network Layer

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An Internet Protocol address (IP address) is a numerical label assigned to each device connected to
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the computer network that uses the Internet protocol for communication an IP address serves two principal
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functions: host or network interface identification and location addressing.
Internet Protocol version 4 (IPv4) defines an IP address as a
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32-bit number.[
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However, because of the growth of the Internet and the depletion of available IPv4 addresses,
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a new version of IP (IPv6), using 128 bits for the IP address.
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When the PDU named segment reaches the Network Layer, this layer adds the IPv4 or IPv6 headers
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to the segment and PDU name is converted to «Packet» in network layer.
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And let's take a look to IP version 4 header now.
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And as you can see that there are lots of fields in IP v4 version header and they are
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version field,
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They are type of service fields, header length field, total length field , fragment offset, protocol, TTL
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header checksum, source and destination IP addresses and IP option.
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Please keep in mind that there are lots of fields in here as you can see.
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lets take a look to ipv4 limitations.
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As we talked in our first slide of our course, almost 50 billion devices will be connected to internet
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by 2020.
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but however Available IPv4 addresses
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are decreasing. In spite of IPv4 is still the most common used protocol,
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it seems like our next step will be IPv6 which can provide a broad ip address range.
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IPv6 provides a huge IP address range and more secure environment. With IPv4, we will not
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Network Address Translation operation which converts
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private ip addresses into public ip addresses.
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And let's take a look to the differences between IPV 4 and IP version 6.
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The first difference is address size. IPV 4 is thirty eight bit number while IP version 6 is one hundred
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and twenty eight bit number.
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The second is address format. IPV 4 is shown in decimal notation.
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As you can see there are dots between the decimal numbers while IP version 6 is shown in hexadecimal
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notation and there is a difference in the prefix notation as well.
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And the biggest difference between these guys is really the number of the addresses that they are supporting.
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As you can see there ipv4 is supporting this and Ip version 6 is supporting a really huge
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number of IP addresses.
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Let's take a look.
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The IP version 6 header now.
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Ipv6 header is pretty straight forward as you can see. on the screen there are 14 fields
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in the IP version for header as you can see version I H-L type of service total length and et
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but there are just 8 fields in ipv6 header and they are version, traffic class
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flow label, payload length…..
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Let's take a look to the routers.
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Now. A router is a Layer 3 network gateway device, meaning that it connects two or more networks and
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that the router operates at the network layer of the OSI model.
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The main function of router is «ip routing» using the routing table entries.
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If you remember from our previous slides, on the switches
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there was a MACaddress table and switches we were making the switching by using the MAC address entries on
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the Mac table.
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But what rotuers are doing is, this is a router
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this guy is keeping a routing table this time routing table which consists of IP Address entries,
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and routers are making IP routing by using the IP address is kept in the routing table.
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And here is backplane of a router as you can see there are some equipments in here, like on off switch
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, like the input power connection, like the gigabit ethernet ports like usb ports and something like that
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if you want to check routers' physical view, deeply there is a great application on Google
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Play store and you can simply go the Google Play store and type Cisco 3D interactive
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catalog and you can check the physical view of the routers deeply there.
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..
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Let's take a look to the router memory now.
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In router memory.
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We have four types of memory.
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The first one is RAM
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The second is ROM.
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And the other ones are NVRAM and the flash. In RAM
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We are storing the running I O S, which is the operating system of the router and the running configuration
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routing and ARP tables and packet buffers. in the ROM
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We are storing the boot up instructions and limited Ios, in the NVRAM we are storing the sturtup config.
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And in the flash we are storing the IOS itself and the other system files.
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And please keep in mind that just ram is valotile.
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So how a router boots up?
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Let's take a look at this.
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The first thing when router is booting up is POST: power on self tests. on this step.
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The hardware is being checked.
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Then ROM loads the bootstrap program and searches for the IOS which is the operating system of
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the router . than iOS is being loaded from the flash and the startup configuration is loaded from the
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NVRAM and in the last step, boot process is completed as everything is loaded into the ram.
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Let's take a look through the routing process.
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If source and destination have same network IDs, source sends the packet directly to the destination
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That's a really important thing that you should keep on your mind.
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But what is a Network ID?
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(network ID) is a portion of the IP address that is used to identify individuals or devices on a network
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such as a local area network or the Internet. On our later section
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We'll see how we can calculate the network ID value as well.
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But If source and destination have different network IDs from each other, source sends the packet to
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A default gateway is the node in a computer network using the Internet
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Protocol Suite that serves as the forwarding host (router) to other networks when no other route specification
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matches the destination IP address of a packet.
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For example in here PC one wants to communicate with the PC 4, they have different network IDs the
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network id of PC one is .1
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network ID of pc 4 is .20, 20 I'm going to show you how I calculate these numbers
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later sections then because they have different network IDs,
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If PC one wants to communicate with the PC 4 , this guy directly throws the packet to the default
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gateway which is the internal interface IP address of this router on the middle.
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But if PC one wants to communicate with the PC two and because they have the same network IDs, the packet
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the packet is not forwarded to default gateway and that is directly forwarded to the PC two.
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So let's take a look how we can configure an IP address for switches.
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Now, if we want to communicate the default gateway on switch the command we're using is IP default-gateway
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and the IP address of the router's internal interface.
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And if you want to configure a default gateway for hosts, for example for this PC, if I want
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to configure the default gateway, on the Internet Options There is a field showing us the default gateway
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I can simply fill this here with the IP address of the default gw configure my host.
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So the next thing we are going to focus on is the routing table. in computer networking routing table
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is a data table stored in a router or a networked computer that lists the best paths to particular network
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destinations.
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and in some cases, metrics (distances) associated with those routes
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The key term in here is the best path.
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For example let's say that you want to go from London to Manchester. what you will do is you open the Google
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Maps perhaps.
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And London is here and Manchester is in here let's say.
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And when you open the Google Maps you use the London to the From field and you enter the Manchester
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to the destination field.
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Then Google Maps shows you a few
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Alternate paths how to how to get from London to Manchester.
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But offers you one best path.
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That's the fastest one.
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So routing table is something like that too in the routing table You will always have the best path for the particular .
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destination.
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In here we're seeing an example of the routing table and we need to type "show ip route" simply to display
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the routing table in here.
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And as you can see in here for example that's a routing table entry which shows us the how we can reach
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the 0.1 network , via1.6.
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It's saying us then that's the best path.
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And in here also we have another best path.
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We have also routing tables on our PCs.And to see our PCs routing table, we can type "route print" on our command window.
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So as I told you if I want to check the router's routing table, I'm typing "show ip route" command and
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I'm seeing the best paths for the particular destinations.
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So how I'm going to examine the routing table entries?
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So in a routing table entry we have some text characters and some numbers as
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you can see the first character is you're seeing on the routing table entry identifies how the network
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was learned by the router.
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For example if this route was learned by statically or learned by a dynamic routing protocol such as maybe
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EIGRP, OSPF or something like that.
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The second field identifies destination to the network.
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Then this field identifies the administrative distance which is the thrustworthiness
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of the route source . then this field identifies the metric to reach to the remote network and this
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field identifies the next hop IP address to reach to the remote network.
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And this field identifies the amount of elapsed time since the network was discovered and here identifies
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the outgoing interface on the router to reach the destination network.
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So let's take a look to router packet forwarding now. Routers
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automatically know the directly connect to networks guys and remote networks must be learned by static routing
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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
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to router zero and say this guy that hey dude if you want to communicate with this network for example
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because this guy knows the directly connected interfaces automatically and this guy does not know anything
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about in here, in here and in here and in here also.
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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
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hey router zero.
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if you want to communicate with the network 2.0 send your packet to for example here
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Or if you are to communicate with 3.0 send your packet to here.
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I can manually configure this or use the dynamic routing protocol saying that if you want to go the
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here use the EIGRP protocol, if you want to go here use the OSPF protocol or something like that.
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I'm going to show you in much deeper on our later sections.
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Again.
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So let's take a look at the basic router configuration now. in a basic router configuration we can simply
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configure hostname for example.
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So let's say that we have a router named
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My router, in the config mode.
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I need to type host name command and I need to give a host name to our device and as soon as I type
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the enter as you can see the host name changed to r0
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And if I want to configure the interface, I need to go to the interface mode by typing interface and
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the name of the interface which is fa 0/1 for this one.
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And I am typing IP address and the IP address of the interface and the subnet mask of the interface.
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All right guys if you could not understand what I'm telling about in here don't worry we are going
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to make separate a wonderful packet tracer
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Lab examples and you'll get
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All of these concepts easily
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Trust me.
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So to verify the interface configuration the command I'm using.
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This time is show IP interface brief and I can check the IP addresses attached to each interface
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by using this command.