INTRODUCTION TO COMPUTER NETWORKS

 

INDEX

1 TYPE OF NETWORKS

1.1 LANS. Local Area Network

1.2 Wide Area Lans    (WAN)

1.3 Metropolitan Area Networks

1.4 Home Area Network (HAN)

2. NETWORK DEVICES

2.1 CLASSIFICATION BY LEVEL

2.2. NETWORK INTERFACES

3. TRANSMISSION MEDIA

3.1 TWISTED PAIR CABLE

3.2 OPTICAL FIBER

4. SWITCHES

5. IP ADRESSES

6. ROUTERS

7. DHCP SERVICE

8. DNS SERVICE

9. PUBLIC AND PRIVATE ADDRESSES

10. WIRELESS NETWORKS

 

 

1. TYPES OF COMPUTER NETWORKS

 

1.1 Local Area Networks

The most  spread networks in organizations are LAN (Local area networks). A Local Area Network is limited to a small area, usually a building or a campus of maximum 200m.

Nowadays, most L.A.N.'s are  Ethernet networks. These networks are characterized by using twisted pair and fiber optic cable as transmission media. Networks using Ethernet divide a stream of data into shorter pieces called frames. Each frame contains source and destination addresses and error-checking data so that damaged frames can be detected, discarded and re-transmitted. The Ethernet standards encompass several wiring and signaling variants. The original Ethernet used a coaxial cable similar to those of TV as a shared medium. Later the coaxial cables were replaced with twisted pair and fiber optic links in conjunction with hubs or switches.

Nowadays there are several forms of Ethernet networks. The most widespread are  Fastethenet which allows a speed of  100Mb / s. Also Gigabit Ethernet networks are becoming common (up to 1000Mb/s)

 

 

Some L.A.N. examples:

• The network of our secondary school,

• An office network,

• the network a small business.

• My home network

 

 

 

 

 

 

1.2 Wide Area Networks

 

 

 

 

1.3 Metropolitan area network (MAN)

A metropolitan area network (MAN) is a network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN).

1.4 Home Area Network (HAN)

A home network or home area network (HAN) is a type of local area network with the purpose to facilitate communication among digital devices in a home. The importance of this networks are steadily rising, due to the spread of digital household devices able to connect to Internet.  

ACTIVITY 1 : Working in groups discuss different examples of networks you know. Write a table with the networks your group has come up with, including the name of the organization, the type of organization and the number of computers you think it is made up. Classify them according their size in  LAN, WAN, MAN and HAN. They must be real networks you, your family, friends or relatives are in in contact or related in some way.

  2. NETWORK DEVICES

2.1 DEVICES CLASSIFICATION

Within a network the devices  can be classified by function  as:

 

CLASSIFICATION	TYPE OF DEVICE	EXAMPLES
LEVEL 1	End devices	Computers,Printers,Tablets,Fax, SMART TV'S, Game Consoles, mobile phone's
LEVEL 2	Devices used to connect devices inside the LAN	Hubs,switches
LEVEL3	Used to connect devices from DIFFERENT LAN's	Routers

Later you will find out why this classification is so important in order to achieve a feasible network simulation.

 

 

2.2 NETWORK INTERFACES

 

A Network card is a device that connects a computer to a computer network, usually a LAN. The Network card is also called a network adapter or NIC (Network Interface Card). There are different types of adapters depending on the type of wire used, (fiber optic, twisted pair), or the architecture used in the network (Ethernet, Fast Ethernet, Gigabit Ethernet, serial interfaces), but currently the most common is the FastEthernet using an RJ-45 connector and twisted pair cable.

Fast Ethernet Network Interface		Serial Network Interface

 

 

The MAC address ("media access control") is an identifier of 48 bits (6 bytes, each represented by two hexadecimal digits) that identifies uniquely a network card. It is also known as physical address. MAC addresses are globally unique, since they are written directly, in binary form, in the network card upon being made. There aren't two NICs in the world with the same MAC address

example of MAC address

 

 

 

3. TRANSMISSION MEDIA

3.1 Twisted pair cable

This cable is made up of a variable number of copper wire pairs that are entangled each other to reduce the electromagnetic noise (interference).

This type of cable is used massively in most local area networks. The Ethernet lan's uses a four twisted pair cable ended in an RJ45 connector like the one shown int the bottom figure.

In Shielded Twisted pair cables (STP) there is a sheet of foil covering the twisted wire pairs to enhance their protection from external interference. This allows increased performance at the cost of a higher price. For this reason this cables are only used in special purposes. The Unshielded variant (known as UTP cable) is the conventional cable found in a typical LAN.

 

 

Twisted pair cable	RJ45 plug	Shielded Twisted Pair cable (STP)

 

 

There are two types of twisted pair connections. The difference is very important in order to carry out correctly the activities that we will perform in the following sessions:

• Direct or straight cable. It is used to connect devices which differ in one level (go over the table of levels above). For instance:

• A Computer (level 1) with a Switch (level 2)

• A Switch (level 2) with a Router (level 3)

• Crossover Cable: Used for connecting devices of the same level or that differ at two levels. For instance:

• A computer (level 1) to another computer (level 1)

• A switch with (level 2) another switch (level 2)

• A computer (level 1) with a router (level 3)

The twisted pair:

1. it is cheap

2. It can only be used over short distances (always less than 100m). This limits their use to Local Area Networks

• Run CISCO Packet Tracer. (Applications->Wine-> Installed applications->Cisco Packet Tracer)

• Select end devices in the device classes pannel (lower left corner). Click on the PC icon (in the picture below it is highlighted with a small blue circle)

 

• When you click on the PC's end Devices category, different types of  computers will appear, as shown below.

 

 

 

 

• Select the first type (the Laptop generic PC) and drag it to the center of the Packet Tracer window. In this way, we will have  set the first PC of our network.

• Drag a second Generic Laptop

• Select the category connections in the device classes pannel (lower left corner). Choose the Z-shaped icon. In the image below it is highlighted by a red circle

 

• Select the direct twisted pair cable. (Cooper Straight). It is the black wire highlighted with a blue circle in the image above.

• Let's connect the two PCs using a direct twisted pair cable: Click on one of the PC's, to deploy its network interfaces list, and choose the only FastEthernet0/0 available. Do the same on the other PC.

 

 

• Remark the red dots at the ends of the connectors. This indicates that the two computers are physically connected but can not exchange data because, for some reason, the connection is invalid. Therefore there is something wrong, and we must fix it in the following steps ....

CONNECTION WITH CROSSOVER CABLE

• The problem is that the PCs are both level 1 devices, thereupon they must be connected with a crossover twisted pair cable. Select the cable between the two PCs. To remove clicking on the item and pressing the delete key

• Select the category  connections in the device classes (lower left).It is the Z-shaped icon highlighted with a blue circle.

 

 

• Select the twisted-pair crossover cable. (Cooper Cross over). It is the discontinued black wire highlighted with a green circle.

• Connect the two PCs with this cable (as  shown below)

 

• The green dots indicate that the link has been successfully established

Now, we will explore the network card of the PC's in order to find out their physical address (MAC address)

• Click on either PCs

• Select the config tab.
  

• In the left column select the network interface FastEthernet0. The configuration network interface window will open.

• The network interface is active and the Mac appears in the MAC Address section. In the case of the image shown below, it is the 0030.A3AA.570C MAC address.
  

 

Save the file and upload it to moodle

3.3 Optical fiber

 

With optical fiber cable connectors	Optical fiber cable

 

• In optical fiber cables data are transmitted by light pulses.

• Optic fiber has a much greater performance than twisted pair.

• The optical fiber can be used to cover large distances.

• It allows data transmission at Gigabit speeds and above (>=1000Mbs)

• They are used for trunk segments of the wide area network

 

ACTIVITY 4. Connecting two PCS through a optical fiber  cable.

In this activity we will do the same we did in the previous session, but connecting the PCs with another type of cable: optical fiber. The computers now have an Ethernet network card with an RJ45 socket, so the first thing we have to do is to change the network card.

• Download from Moodle your personalized Cisco Packed Tracer file and save it as practica2.pka

• Add two generic PCs (this time two desktop Generic PCs. Click on the icon left the one you used in the former activity)

• Click on PC0

• Select the tab physical

• Remember that we will change the PC's network card, which by default is a twisted pair cable card, for a fiber optics card. To change a network card firstly we have to shut down the computer. Click on the power button to turn it off.

• Now look at the bottom of the PC. It shows a twisted pair RJ-45 socket. This is the network card that we are going to change.

• Now the card slot is empty. You can drag the optical fiber card on it. In the module pannel click on the PT-HOST-NM-1FFE card and drag it on the empty slot

 

 

• Turn on the PC by clicking the power button

• Repeat the same steps on the other PC, installing in it another optical fiber card.

• Finally you have to connect the two PC's with an optical fiber cable. Select the media category and select the optical fiber cable in the the far right of the pannel

 

 

 

• If you've done everything right the red dot on both sides of the connection will turn green meaning that the two PCs are properly connected .

 

Save your activity and upload it to Moodle

 

Two PC's connected by a cable are not a computer network. What if we want to connect 10 computers together? Do we need to install 10 Network cards in any PC in order to get them interconnected?? That's not obviously a good solution.

Activity 5. Setting up a 4 computers network

• Drag to the Packet Tracer screen 4 pc's generic (two laptops and two desktops)

• Select the category Switches in the device classes area. Choose a switch type 2960

 

• Connect each of the 4 PCs to the switch. All connections should appear in green

• Rename the PCs. To do this click on a computer, select Config tab. The names entered are: Address, Secretariat, Human Resources, Accounting

   

 

Save the file and upload it to Moodle

 

 

ACTIVITY 6. SETTING UP A RING NETWORK

A ring network is a network in which all computers are connected together forming a ring

 

 

The main drawback of ring networks is that in order to close the ring, you need two network cards per computer. In Packet Tracer a generic PC  has only a network card. Therefore instead of using generic PCs desktop we will use a device called Generic Server

• Turn Off the Server (by pressing the power button, which is just below the red circle)

• Add a second network card to the server, dragging PT-HOST-NM-1CGE to the  empty slot (highlighted above by the red circle)

• Draw the links between the  4 pc's to form the ring network. Turn on the computers and check out all the red dots change to green
  

5. IP ADDRESS

We  know yet an addressing mechanism in networks: the physical addressing or Mac address in the network cards. However this type of addressing, is not suitable for large networks for different reasons. One of the most important is that for users would it's too difficult to dial a hexadecimal number of 8 digits as 0030A3AA570C

Internally, computers directly wired use physical addressing to communicate among them. However, both for small networks as for huge ones as the Internet, is used a routing mechanism called IP address (IP stands for Internet Protocol). In brief, this is how it works:

• Each network card of a computer is assigned an IP address and a network mask. If your computer has multiple network cards  then you should have have multiple Ip addresses
  

• Each computer network is also assigned a network address.

The IP address is made up of 4 digits ranging from 0 to 255 and separated by a dot. Examples of proper IP addresses would be:

192.168.100.2

221.200.0.11

11.23.2.112

E    Examples of incorrect IP addresses would be:

258 .33.2.3- There's a digit over 255

0 .3.2.3 - The first digit can not be 0

255.255 .243.12- address 255 is reserved

232.223.44.33 .22- are five digits instead of 4

The IP address is divided in two parts

• Network Address : The part of the IP address that identifies the network the station belongs to. In the whole Internet two networks never could have the same network address
  

• Host or station address is a number that identifies a computers within its own network

 

In the image above there are two networks. The network on the left has a 192.168.18.0  network address. All computers in each of the networks share the same network address and differ by having a different  host number. Therefore in the left network the computers are identified by the following IP addresses

192.168.18 . 99

192.168.18 .11

192.168.18 .22

192.168.18 .33

 

The network identifier of the right network is 192.168.5.0. and the host numbers are:

 

 192.168.5.11

 192.168.5.22

 192.168.5.33

Pay attention to the following statement because it is very important.

In an IP network, although two computers are connected to the same cable, they can only communicate with each other, if they have the same network address

A mask is used in order to distinguish which part of the IP address is the network address and the host address. The mask is a 4 digits among 0 and 255 and separated by points. Though in real networks there are many different masks, in this unit we will consider only three possible masks

Mask	Meaning
255.0.0.0	The first digit is the network address, the rest are station addresses
255.255.0.0	The first and second digits are the network address, the rest are station addresses
255.255.255.0	The first, second and third digits are the network address, the rest are station addresses

E.g.

IP Address	Mask	Network address	Host address
221.23.22.33	255.255.0.0	221.23.0.0	22.33
180.12.22.1	255.255.255.0	180.12.22.0	1
21.23.222.1	255.0.0.0	21.0.0.0	23.222.1
123.12.3.1	255.255.0.0	123.12.0.0	.3.1
89.234.33.22	255.255.255.0	89.234.33.0	22

 

Activity 7 Designing Ip addresses for a 8 hosts network.

 

• The starting point of this activity is the file you submitted in the activity 6. Open it and save it as activity7.pka

• Rename the Pcs as PC1, PC2, PC3, PC4. To rename a computer, just click on the name and write over it

• Add another 4 pc's, and another switch to interconnect them. The PCs will be called PC5, PC6, PC7, PC8

• Connect the two switches. Remember,  to connect devices of the same level you must use a  crossover cable
  

 

Now all PCs seem to be connected. However they still can not send or receive anything because they have no IP addresses neither any network masks

 

• Click on PC1. Its properties window will open.

• Select the Desktop tab

• Select the IP Configuration icon. The following window opens

Just fill in the IP Configuration section with the following data

 

• Enter  192.168.30.1  in the IP address box

• Enter 255.255.255.0 in the Subnet mask box

Configure the other computers with the following IP addresses and masks, following the explained procedure

Computer	IP Address	Masks
PC1	192.168.30.1	255.255.255.0
PC2	192.168.30.2	255.255.255.0
PC3	172.16.20.3	255.255.0.0
PC4	172.16.20.4	255.255.0.0
PC5	192.168.30.5	255.255.255.0
PC6	192.168.30.6	255.255.255.0
PC7	172.16.20.7	255.255.0.0
PC8	172.16.20.8	255.255.0.0

Notice that what we have done is to set up two different networks.

 

• The PC1, PC2, PC5, PC6  computers belong to the network 192.168. 3 0.0

• The PC3, PC4, PC7, PC8 computers belong to the network 172.160.0. 0

Remember the rule: although they are connected, only those computers who have the same network address can exchange data packets. We are going to check out  whether this rule is true

 

• Click on PC1. Its properties window will deploy.
  

• Select the Desktop tab

• Choose the Command Prompt icon

  Let's test if PC1 and PC5 are recognized in the network. To do this we use the command PING ipaddress. This command sends 4 data packets to the destination IP address and waits for an answer of each of them. If the command reports that the response packets are received we can be certain that the two computers  are properly connected and on the same network

• Write ping 192.168.30.5 and press enter.

 

• Write ping 172.16. 2 0.4 and press enter

Save the file  and upload it to Moodle

6. ROUTERS

So far, we have learned that it is not possible to connect two computers that are not configured with an IP address belonging to the same network address. However this does not match at all with our everyday experience. When we connect to the internet, we are able to connect with millions of computers each of which is in a completely different network address. This is possible thanks to another kind of devices: the routers.

A router is a device that allows connection between networks with different network addresses. An example

In the network shown in the image there are two computer networks, both with the mask 255.255.255.0. PCs from the top left network belong to the 192.168.200.0 network address, and the bottom right computers are on the  192.168.1.0 address network. Therefore they are not able to  communicate each other.

The router is the round sampled device in the middle of the network. Notice it is linked with both networks. A router is a third level device, which two or more network interfaces in order to be connected to two or more networks. The function of the router is to allow communication between the computers on different networks

When H8 wants to send a data packet to H3 wich is a computer out of its own network, it sends it to the Router. The router looks into  the destination address, and 'routes' the packet to the correct output (that is, it sends the packet for the network interface connected to the network where  H3 is located)

Therefore the computers in a network, in order to be able to communicate with other networks, must be configured with the IP address and network mask of the router interface connected to them. This interface is called a GATEWAY.

ACTIVITY 8. Using CISCO Packet Tracer design the network shown in the figure above.

• You are supposed to be able to do the  following firsts steps.
  

• Place two switches

• Place 8 PCs and connect them to the switches using the fastethernet interfaces
  

• Look up the image and set up the IP addresses and masks for every computer. Remember that the mask is in all cases must be 255.255.255.0

• Place and configure a router:

• Select the type of device as a router in the bottom left of Packet Tracer. Drag the first router (1841) to the screen

 

• The router has two FastEthernet interfaces marked as Fa0/0 and Fa0/1, connect both switches to the router using these interfaces

• Now we have to put an IP address and mask to interfaces of the routers. Click on the router

• Select the Settings tab

 

• In the left column select FastEthernet0/0

 

• Fill the IP address from the network to which it will be connected, for example 192.168.200.254

• Write the network mask

• Enable the network interface by clicking Port status ..On

• Select the other network interface (FastEthernet0 / 1).

• Write the  IP address and mask assigned to this  Network Interface (192.168.1.254 /255.255.255.0)
  

• Finally you must configure in each PC the IP address of the Gateway. Remember the Gateway is the IP address of the router interface connected to your network, ie 192.168.1.254 or 192.168.200.254

• Click on PCs

• Click on the desktop tab

• Select IP configuration

• Put the address of the gateway in the Default Gateway box.

   

   

We must test if it is working. If all goes right, we will be able to ping from H3 to H8 and receive a "pong".

 

• Make sure the Router is connected with the correct IP addresses

• Click on H3

• Click on the desktop tab

• Select Command Prompt

• Write PING 192.168.1.4. Remember, the test is successful if a messages like 'Reply from 192.168.1.4 bytes = .. .. TTL = time = ..'  is received

• Call the teacher for help if the ping response shows "Request Time out 'or if the response is of type' Reply from 192.168.200.254 Host Unreachable"

Save the activity as activity 6 and upload it to Moodle


ACTIVITY 9 Make the Quiz 1 in Moodle.  It's a 10 questions test with multiple choice answers. You can use both this text and any information you find on the Internet so solve it. But keep in mind that you will be allowed only one attempt.

1. The optical fiber  cable is suitable for data transmission
Select one:

2.Twisted pair cable consists of a variable number of pairs of wires 
Select one:

3.To directly connect two devices of the same type (two routers, or two switches, for example) it is necessary to unite them with:
Select one:

4.The physical address or MAC address is:
Select one:

5. Devices A and C
Select one:

6. To form a network, computers must...
Select one:

 

7. 195.11.195.1 is a valid IP address
Select the correct:

8. If  PC2 pings PC5, will it get an answer?

9. 255.11.114.1 is a valid IP address
Select one:

10. The discontinnued line between the two switches indicates that the connection is intermittent

1. true
2. false

 

7. DHCP

 

So far, we are setting the IP addresses manually in every computer. In a network with many computers scattered throughout a large geographical area this brings about lots of work and serious problems. For instance: two different computers might  get accidentally the same IP address, that's a serious problem. Or someone will have to change the IP address anytime a computer is changed of LAN. Thats  a lot of work. There is a protocol called DHCP that provides a better solution. In DHCP, whenever a network computer boots up, it looks for a DHCP server on the network, and ask it an IP configuration. DHCP servers assigns correct IP addresses avoiding repeated configurations in the network

ACTIVITY 10. DHCP

 

• We will perform the following network of 4 computers. Just drag the PC's and connect them without any additional settings.
  

 

• Click on each of the PC's. Select the Desktop tab. Select the IP Configuration icon. Make sure that DHCP is enabled on the four PC's, as shown in the picture below

 

 

• Now is the time to drop in the network  a DHCP server. Select the bottom left class devices pannel in Packet Tracer. Select the category End devices and select a device type Generic Server.

 

•  

  Drag the Generic Server to the main screen of Packet Tracer and connect it to the switch.
  

• You must manually set the IP configuration of the DHCP server. Click on the server, and select the tab Desktop. Select the IP configuration icon. Enter the values ​​shown in the picture under this paragraph

 

• We will configure the server to provide DHCP service to the rest of the network. Click the Server and select the Settings tab. In this window on the left  there is a column pannel with several buttons. Under the section Services you will find the button DHCP. Press it and the DHCP configuration window will open:

   

 

 

• In this window we will set the IP configuration of the DHCP server.

• The default gateway (Default Gateway) will be 172.20.20.1

• The DNS server address is 172.20.20.200

• Start IP address indicates what will be the first IP address that the server can assign to a PC (and its  mask). Put 172.20.20.2 This is important to understand, we started at the 2, because the 172.20.20.1 has already been assigned to the Default Gateway. Remember that the network can not have two devices with the same IP address.
  

• Maximum number of Users means the number of IP addresses to be assigned from the Start Ip address. If you enter 50 the server will grant up to 50 IP addresses starting with the 172.20.20.2, and continuing with the 172.20.20.3, 172.20.20 4 ... until 172.20.20.51. In this case you can put any number lower or equal to 198. Imagine you  put 199, the last available address to grant would be the  172.20.20.200, and that is the one reserved to the  DNS server.

• Click on the DHCP ON button on the top of the window to start the service
  

• Click the button save when finished. The result should look like the following:

 

•  

  Click on any PC, and  select the desktop tab. Select the icon IP config . A complete IP configuration should be loaded from the server as it appears in the picture. If not, click the button Static and then again on DHCP

 

Upload to Moodle the  Activity 10

 

8. Domain Name System (DNS)

 

Domain Name System or DNS is a system for naming computers connected to the Internet or a private network . For most people it's difficult to memorize numbers as an IP addresses. Instead humans are good at memorizing words, so it is much easier for a human to remember something like www.amazon.com than its equivalent IP address. This is the reason why the DNS system was developed: to translate (resolve) names intelligible to humans to IP addresses with the purpose of locating and routing equipment worldwide on the Internet.

 

 

DNS names are based on a hierarchy. All Internet names must have a primary domain name as com, org, net, UN, es, fr, it etc. These names are useful classifying Internet servers by its main function. Commercial companies take the .com domain. The nonprofit organizations often use .org. Another possibility is to identify the country where their server is located. In the case of Spanish organization and companies the primary domain is .es

Left to  the primary domain, and separated by a dot, comes the domain name of the organization. This is the word used to identify that company on the Internet. Examples are amazon.com, ebay.com, elpais.es, hotmail.com.

Some organizations add a subdomain. For example the Valencian Goverment uses the domain gva.es. But the Education Department,  uses the domain edu.gva.es

The last component of a DNS name is the name of the server within the domain. For example, the Antares computer, in the Education Department would use the following dns name:

antares.edu.gva.es

By the way, when accessing any website with a name that begins with www, for instance: www.elpais.es , we are connecting to a computer named www, which belongs to the specified domain, in this case elpais.es . Organizations always puts his web servers the name www, to make predictable for user the name of their web site.

DNS servers

On Internet someone has to do the translation (resolution) of a name into an IP address and vice versa. The Internet consists of billions of computers, so it is impossible to put all them in a unique data base shared by all DNS servers. This Database would be too huge and it would be impossible to  deal with all the constant updates. DNS is based on a distributed database in which there are multiple DNS servers each responsible for its own section of  Internet and depending on a higher authority over them. For this reason has been  established the  following hierarchy of DNS servers

• LOCAL DNS SERVERS:  Each local network must have a local DNS server. This server only knows the names and IP addresses of the computers on its local network, and the names and IP addresses of the Internet root servers

• DNS root servers. There are only 13 Internet root servers. In  the image above they are shown in the highest level (the balloon containing a point). The root servers only know the name and IP addresses of the top-level domains DNS servers (second row in the image above) as: com, org, net. es, fr, etc.

• FIRST LEVEL DNS SERVERS:  The first level DNS servers know the names and IP addresses of the DNS servers for each domain hanging from them. For example, the COM domain DNS servers know the names and IP addresses of all DNS servers of COM domains, such as AMAZON.COM, EBAY.COM, YOUTUBE.COM, HOTMAIL.COM

• SECOND LEVEL DNS SERVERS: The second-level DNS servers know the names and IP addresses from a specific domain. For example there are one or more DNS servers in the second-level domain AMAZON.COM, who know the IP address of each of the computers that are in amazon.com. That is, the server is able to translate www.amazon.com or ftp.amazon.com , or smtp.amazon.com to IP addresses.

When a user puts in your browser the URL www.wikipedia.com  the resolution of this name goes as follows:

 

 

 

• Your  browser asks the DNS server on your local network wich is de IP address of www.wikipedia.org
  

• The local DNS server looks up in its database if it has an IP address for www.wikipedia.org. If it is not found, the local DNS server asks the root server which is the IP address of the firsts level DNS server in the  org domain 

• The local DNS server asks the  orgDNS server which is the IP address of the DNS server in the wikipedia.org domain.
  

• The local DNS server asks the wikipedia.org DNS server   which is the IP address of the computer called www.

ACTIVITY 11. Your group must search on Internet information about the root servers on Internet, and then answer the following questions:

• How many root servers are there?
• Where are they located?
• What do you think would happen if all them got down simultaneously?
• Where is the dns server for the .com primary domain?

 

ACTIVITY 12. INSTALLING A DNS SERVER

 

• We will perform the following network of four computers. Drag the four computers, and connect them as shown in the image below

   

 

• Click on each of the computers. Select the Desktop tab. Select the IP Configuration icon. Make sure you are pressing the Static button. Assign them the following IP addresses

PC0	172.16.10.10/255.255.0.0
PC1	172.16.10.11/255.255.0.0
PC2	172.16.10.12/255.255.0.0
PC3	172.16.10.13/255.255.0.0

 

 

• This network still does not have a DNS server. This means that  to transfer a data packet the sender must know the destination IP addresses. For example:
  

• Enter the tab desktop of PC1, and click on command prompt

• Enter the command ping 192.168.10.13 the command will report a  successful connection.

•  

   But if you write Ping PC3 it will fail (in fact, it will take a few minutes to show the error message)

 

 

• Now is the time to introduce a DNS server in your network. In the bottom left corner of Packet Tracer select the class devices pannel and choose  the End devices category. Select the device Generic Server.

 

 

• Drag the generic server to the main screen of Packet Tracer and connect it to the switch.

 

• You must state the IP configuration on the DNS server. Click on the server,  select the tab desktop. Select the IP configuration icon. Enter the values ​​shown in the picture under this paragraph

 

• We are going to configure the server to provide DNS service to the rest of the network. Click the Server and select the Settings tab. In this window you have on the left a column with lots of buttons. Under section Services you have the DNS button. Press it and the window will show this form (see image below):

   

 

 

• The next step is to indicate which is the DNS server name and IP addresses of the computers on it. Let's start with PC0. In the edit box Name write PC0. Check that in the field TYPE there is an  A Record. In the box Address write 172.16 .10.10. Click the button Add

 

 

• Repeat the same steps for each of the other network computers (PC1, PC2, PC3)

• Press the ON on the DNS Service area
  

 

 

• The DNS server are now already running but the PCs on the network still don't know it. You must specify the IP address of the DNS server in the IP configuration in each computer on  the network.

• Click on a PC, select desktop. Select the icon IP configuration

• The DNS server box must be filled in with the DNS server address (it should be 172.16.10.1 if you followed the instructions)
  

• The last step  is to verify that the DNS system is working properly pinging  one PC from another using its name instead of its IP address

 

UPLOAD TO MOODLE THE ACTIVITY

9. PUBLIC AND PRIVATE IP ADDRESSES

 

When the IP protocol was developed, it was thought that 32 bits (four numbers from 0 to254) would be enough to assign an IP address to  every computer in the world, because there were 4.294.967.296  of them.

This number of IP addresses can seem enormous. But actually the world has nearly run out of them.

ACTIVITY 13:

Work out how many IP addresses do you need in your home. You must add up an IP address for every mobile phone, every tablet, every PC, every e-Book (most allow Internet access), each Smart TV, game console, media players, network disks, NAS servers and any other wireless device in your home ( yours or belonging to your family members).  Nowadays even Power and water supply counters are connected to Internet.

Fill the following table:

 

DEVICE	STUDENT 1	STUDENT 2	STUDENT 3	TOTAL
Family members
Computers
Mobile phones
Tablets
SMART TV
E-Books
Game consoles
iPODs -Mp3's
DIGITAL  COUNTERS (Power and water suply)
Other devices
TOTAL

Estimate the number of IP addresses you, and your family members need in other places as  in their job, their bussiness or your school.

 

	student 1	Student 2	Student 3	TOTAL
At work/business
At school/University
TOTAL

Estimate how many Ip addresses are needed in the world. Consider  there are about 2 billion people in the developed wold, 7 billion people in global. And estimate  the average for  people in the undeveloped countries as 1/4 the figure you have calculated for the developed world.

what do you think, the world is running out of IP addresses or there are still plenty of them??

Upload your answers to moodle

 

There are several solutions to this problem: the main solution is  the IPV6 protocol. IPv6 addresses are made of 128 bits (32 hexadecimal digits), which results in 2¹³⁸ IPv6 addresses. This means a staggering 6.7 trillion IPV6 addresses per square millimeter on the planet. It is foreseeable that there wont be any  scarcity of IPv6 address over a long period of time.

But until IPv6 is fully introduced, the only way to save IP addresses is the world is the  private and public system of IP's directions.

• A public IP address is a real IP address, which can be used on the Internet to access any computer connected to the global network. It would be equivalent to a mobile phone number.

• Private IP address are ranges of addresses restricted to local networks. Its equivalent in telephony would be the telephone extensions. In an organization with a local area network, computers use private IP addresses, and the only devices that have a public IP address are those on the edge of the network, that is the routers. This saves public IP addresses but has a drawback: the computers with private IP address can not access the Internet by themselves, and they need to be assisted by a router or other network devices with a valid public IP address.

 

Using this trick we save many millions of public IP addresses. Before this system, an organization with 1000 computers needed 1000 public IP's. Now it only might need one Ip public address for its router. The other 999 computers would use private IP and when they would need to access the Internet, they will ask its  router to do it for them. Private IP addresses can be reused again and again in computers belonging to differents LANs reducing drastically the number of public IP's the world needs.

At home for example, even if you have multiple network enabled devices, only the router has a public IP address provided by your ISP. Other devices on your local network are private IP addresses assigned by your router.

The following table shows the private IP addresses ranges

 

• The class A  IP addresses are associated with the  255.0.0.0. mask There is only one private network A class address, but it can have up to 16 million stations

• The class B IP addresses are associated with the  255.255.0.0. mask. There are 16 private class B network addresses, and any of them can have up to 32,000 stations

• The Class C IP addresses are associated with the  255.255.255.0 mask. There are 256 private Class C network addresses , and each one can have up to 256 stations

ACTIVITY 14. public IP addresses.

In order to do this activity you need to log in our Moodle  and download the file simulación_internet.pka. In this file a cloud of routers simulates how the Internet works.

 

• Open with Packet Tracer the file you have downloaded from Moodle. In this network internet is modeled as a cloud of routers. To connect a computer to the Internet just connect it to a router of the cloud. Two end devices simulate a DNS and Web server on the domain www.servicios.com.
  

• At the bottom of the screen you have a Linksys router. This device is very similar to the wireless router  you probably have at home

 

• Connect two PCs to each of the wireless routers marked with the name PRIVATE NETWORK ROUTER A PRIVATE NETWORK ROUTER B ROUTER PRIVATE NETWORK C. Use twisted-pair Direct cable

• Make the IP configuration of each PC. The IP address you have to put on each PC is shown  in the image below: on the left 192.168.0.2/255.255.255.0 Pc. On the right 192.168.0.3/255.255.255.0

• The gateway will be  192.168.0..1 and the  DNS server address is 201.0.20.254 for all PCs

 

• Verify that the PCs have internet access:

• Click desktop -> Internet browser in PC

• Write www.servicios.com and press GO. You should be able to access the web page of the site, though it may take a couple of minutes

 

• There is something wrong in this networking scheme. It shouldn't work because several hosts have the same IP address. For example, imagine that in the first network the PC A pings to192 .168.0.3, which of the three computers with 192 .168.0.3 IP address should answer?? It is as if three people had the same mobile phone number
  

• But the network actually works because the network address 192.168.0.0 is a private network address that does not apply outside the local network. It allows hosts to be identified within the same network, not outside it.

• To access the Internet, the hosts must use a router. In each subnet the only device with a public IP address is the Router LAN interface

• Put the cursor on the router and verify that the interface called Internet has a public IP address. That is, in a range different from those listed above

UPLOAD TO MOODLE  THIS ACTIVIY

ACTIVITY 15 local network for a school.

In this activity we are going to build a local network for a school where there will be two classrooms equipped with 10 computers.

 

• The classroom one should use the private network address of class C 192.168.0.0.

• Classroom 2 computers must use the private network of class B 172.16.0.0
  

• In the right part of the network shown in the image above there are two linksys routers called CLASS 1 Network  AND CLASS 2 Network. You need to connect each of the networks to one of these routers

• Note that the Linksys routers allow connection of up to 4 computers. But you have to connect 10. Therefore you need a switch in each of the networks

• We must make a small modification in the Linksys router configuration in order to use them to connect the hosts to Internet
  

• Click on one of the two Linksys routers

• • Select the GUI tab. The window below appears

   

 

 

• In the Network Setup section, you must change the IP address of the router for the first IP address of the private network that you have chosen. For example, if your private address is 192.168.0.0, you should allocate to the router  the address 192.168.0.1. If you use instead 172.16.0.0, you should put 172.16.0.1. But remember, once allocated, you are not allowed to use any of these network addresses. After making the change you have to scroll down the screen until you reach the blue button save changes and click on to save the changes

• In each PC on the network, you have to put a

• An IP address

• A network mask. Remember, for class B networks is 255.255.0.0 mask. For networks of class C the mask should be 255.255.255.0

• An address Gateway. Here you must put the private address  on the Linksys router to which it is connected

• DNS server address.  201.0.20.254

• In order to consider complete the activity, you must been able to access www.servicios.com

Save the file and upload it  to moodle.

 

ACTIVITY 16. Local network with DHCP server

In the previous activity we have built a small local network with static IP addresses, that is, the network administrator (you)  had to set up each computer IP individually.  However, in a Linksys wireless router, we can enable the DHCP service so that the router could assign IP addresses dynamically.

Open the file Simulación_internet.pka  and save it as activity16.

Follow the next steps:

 

• Connect a switch type 2950 to the Linksys router name Red Class 1 . Remember that these Linksys routers are designed for the domestic market, and are both a router and a switch (it has    5 Fastethernet ports). When connecting the switch 2950 use a twisted pair crossed cable,  because we are connecting a switch with a switch, and are (two same level devices).

 

• Drag 6 PC's and connect them to the switch. These PCs currently have no IP configuration. Rename them as A1, A2, A3 ...

• The next step is to enable the DHCP service on the Linksys router. To do this click on the Linksys router, select the GUI tab, and scroll down the screen to the section network configuration. Put the IP address 192.168.1.1 .

• Activate the DHCP service clicking the button enable (see image below)

• Introduce the range of IP addresses to hand out. we are going to distribute 50 IP addresses starting at 192.168.1.100 (and ending  at 192.168.1.149)

• Don't forget to click the Save Settings button to save the changes.

 

• On each PC, click on it, display the desktop tab, and select IP configuration. When you select dynamic there,  wait for  a moment and the router will automatically assign a dynamic IP address
  
  
  

10. WIRELESS COMMUNICATION (WIFI)

 

Wireless communication (WIFI)

WIFI is a mechanism for connecting electronic devices wireless. In a wireless communication the medium  used is shared (the cable is the air!!!), and this has many negative implications. However the advantages make it afford to get over the problems: the stations can be mobile and no cable is needed. That is the reason why WIFI networks are thriving

 

• As the medium is shared by many users, there must be a sharing mechanisms allowing an ordered access to the shared media. If all hosts transmit at the same time, all communications  will be mixed up and no one will receive anything. The following issues must be sorted out:

• The need to limit the WIFI scope to a small range, in order to limit interference among WIFI LANs who are very close to each other. Domestic wireless communications have an effective range of 20m indoors and up to 100m outdoors. The range decreases with obstacles between transmitter and receiver. 20m indoors can be reduced to 8 or less if there is a wall in the middle.

   

• The need to split the channel into frequency bands, so that each user uses a channel portion. (Conventional radio stations do the same, each operates in a frequency band that does not interfere with the others).

• As the medium is shared by many users, we will have to solve some security threats:

   

• All users can potentially intercept and hear my wireless communications. -> Need for encrypted communications

• Need to protect the access point. The access point is an Internet gateway that can potentially be used by anyone with a wireless device nearby. It must be protected to prevent other users consume bandwidth while you're paying for it to your Internet provider.

 

ACTIVITY 17. WIRELESS NETWORK

In  this activity we are going  to recreate a home network for a family of three, Juan, Maria, and his son Juanito

 

• Start Packet Tracer and open the file simulación_Internet.pka

• Select the category wireless devices

 

• Select the Linksys device and drag it to the screen. Note that you are going to connect it to the router 110, so place it near it

• Select the type category end devices

• Drag  the following devices.

• A computer. Name it JUAN PC

• A generic server. Name it Xbox 360

• A Laptop. Laptop Name it MARIA

• A smart device Name it SMART TV

• A smart device Name it Iphone Juan

• A smart device Name it Iphone Maria

• A tablet: Name it JUANITO

 

 

•   Click on the router Linksys. It has 4 FastEthernet ports and a port labeled Internet. This device is not only a router but a combination of an Ethernet Switch Router + Wireless Switch + Server + NAT + DHCP server.

=

 

Router as Fast Ethernet and Wireless SWITCH

• The 4  Fastethernet ports work like a switch. The devices connected to them can communicate  among them provided they are on the same network. We use these ports to connect wired devices to Internet: Connect the PC and the Xbox to the FastEthernet interfaces using twisted-pair straight cable

• Put all the wireless devices in a position near the router. You will see that immediately a wireless connection is established, shown as a discontinued line.

• A laptop by definition is a mobile device, and having a wireless router in our network, it makes no sense to connect it by cable. Change the network card laptop, to a wireless card. We have done this before:

• Turn off the laptop, by clicking the button (tab physical)

• Take away the current network card. Drag the portable module Fastethernet network to the dark rectangle in the bottom right of the screen.

•  
  Now the card slot is empty. Select a Laptop- PT-1-NM-W module and drag it over the slot.

   

 

 

• Turn on the  laptop again, you'll see  immediately how it connect to the network

The router as DHCP server

 

Let's check connectivity by pinging between the PC of John, Mary, Iphone and Xbox.

 

• Click on the PC JUAN, select the Desktop tab, select IP configuration, and select the DHCP button. Immediately the machine should obtain an IP address from the router. 

• Perform the same process to the Xbox

• In the case of Maria's Iphone DHCP is the default setting. You can check which  IP address has been allocated to it, by clicking DeskTop-> comand prompt. Write IPCONFIG. Record the IP address

• Make ping between the three devices to test connectivity.

 

Connecting the Linksys to the router 110.

• Connect with a twisted pair cable the port marked as Internet in the Linksys to the Interface  Gigabit Ethernet 0 on router 110. Both devices are of the same level, so you have to connect them with a Crossover cable
  

• Set the Gigabit Ethernet interface 0 of the router 110 with the IP address 192.23.45.1

• Set the public network IP 192.23.45.0 in the RIP protocol, in order to propagate it to the rest of the routers (select the tab config router 110, select RIP in the left column and add the network 192.23.45.0)

• Click on the Linksys router. Select the GUI tab. The router configuration interface appears must appear as shon below

   

 

• Typically routers provide a web server that allows to setup them. To configure the router, you can access the configuration tool using the browser of any computer on the network address 192.168.0.1. Obviously, the router must be protected by a username and password, otherwise any network user could enter this website and change your router configuration. We are going to change the router password:

• click on the Gui tab in the router and select the menu item Administration

• Set a password for the router. Write cisco as router password and  admin as username

• Click the PC JUAN. Select desktop

• Start the web browser. Set router IP address to 192.168.0.1

• It's  asking  you  for a username and  password . The user should be admin in the vast majority of the routers. The password was set up in the previous step: cisco
• We're on the website of router configuration. The following step is to set up the router. Look at the welcome screen Linksys router

 

=

• Remember that this device is equivalent to normal router, plus a wireless router, plus a wired switch. The local network devices are connected to the switch ports, and the router acts as a DHCP and NAT server for this devices. On the other hand, the router is the only device on the network that  is actually connected to the Internet. In its Internet interface, the router must have a public ip (not a private one). This IP address is provided by the ISP  (the service provider) through DHCP. In this way,  the option shown in the picture is by default enabled.
  

But in our simulation the router 160 is not a DHCP server and  the IP address of the router Ethernet interface have to be set up manually.

 

• Display options and choose static IP address

• Enter the IP address 192.23.45.2/255.255.255.0

• Fill in The gateway box will the router public address, (ie 192.23.45.1)

• Click the Save Settings button to save your changes

 

• If all was right, the computers should be connected to the Internet. Let's check connectivity by pinging from some PC to the DNS root server. For instance, use  Juan laptop   for pinging 85.0.0.2. If you do not get a positive response asks the teacher for help.

Save the file and upload it to Moodle.