Identify network hardware and protocols · l To visualise this concept of layers, ... l The protocols used within the Internet were designed using a layered model ... l The application

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Identify network hardware and

protocols

Contents1 Layered network protocols 32 TCP/IP reference model 43 Application layer 54 Transport layer 65 Internet layer 96 Network access layer 107 Network hardware 12

7.1 Transmission media 127.2 Network devices 15

8 Network address translation 249 Using networks securely 2810 Malware 2911 Phishing 2912 Activities 3113 Resources 3314 End of course quiz 3315 Acknowledgements 34

2 of 34 Monday 4 September 2017

1 Layered network protocols

l Network communication relies upon the interaction of many different protocols.These protocols are designed to implement a particular set of rules and conventionsgoverning particular aspects of how devices in a network communicate.

l Network protocols are arranged in layers, with each layer providing a specialisedservice for the layer above. Because each layer consists of standardised protocolsthat perform functions to an agreed set of rules, it is possible to modify individualprotocols within a layer without having to change protocols in other layers.

l To visualise this concept of layers, consider a conversation between two people:l Content layer: ideas exchanged in conversation.l Rules: agree to speak a common language, take turns speaking, not to interrupt

when others are speaking.l Physical: face-to-face communication requires speakers to be close enough to

hear each other.l In this example, the conversation has been divided into three layers. The physical

layer considers the fundamental requirements of exchanging information betweentwo people using speech. This includes considering the distance between thespeakers, which will affect how loud each person needs to talk in order for the otherto hear. Speech is a movement of air, which is translated as sound waves. Thismeans that the conversation could take place in a ‘near’ vacuum like outer space.

l The rules layer defines how the speakers will talk. To exchange information, acommon language would need to be chosen. Once the language is agreed, how isthe conversation to be managed? Taking turns is a reasonable way to converse withanother person and interrupting would be considered rude. But what happens if oneperson misses something and wishes it to be repeated? Do they ask for it to berepeated verbally, or do they use an agreed signal such as raising a hand?

l The content layer considers the actual message exchanged between the twospeakers, which in a conversation may be an item of news, plans for a holiday or justgossip.

l By dividing the conversation into layers, we have decided upon the particularfunctions that are required by each layer to support communication, and in oursimple layered model, it should be possible to change some aspects within one layerwithout affecting the others. For example, if we now decide to have a telephoneconversation, how does this change the requirements of our physical layer?

l Networking protocols can be layered in a similar manner to the voice conversation inthe example above, but has a wider range of considerations and uses differentterms:l Encoding: language to use.l Formatting: greeting, recipient identity, closing phrase, sender identity.l Message size: segmentation of data.l Timing: flow control and timeout.l Delivery: to one host (unicast), to all hosts (broadcast), to some hosts

(multicast).We will discuss these terms in more detail as you progress through the course.

1 Layered network protocols


2 TCP/IP reference model

l The protocols used within the Internet were designed using a layered model referredto as the TCP/IP reference model:

Figure 1

l These protocols operate on your computing devices, and allow the programs youuse to access the data network via the single network interface card (NIC) that isfitted to most devices. Imagine how difficult this task would be for your device if you

2 TCP/IP reference model


used multiple programs that required network access – for example, surfing theWorld Wide Web (WWW), downloading a file and sending an email.

l All these different programs expect to be able to simultaneously access your NIC inorder to send and receive data. The purpose of the TCP/IP reference model is toallow the design and creation of protocols that can support the network requirementsof various installed programs competing for the attention of a single NIC.

l Each layer of the model defines the function of the protocols that operate within it:l Application: provides the interface between the other layers and the operating

system software on your computing device.l Transport: manages application layer data and prepares it for transmission by

segmenting it into easily manageable blocks. It is also responsible for allowingmultiple programs to simultaneously access the NIC, and managing the reliabledelivery of data if required.

l Internet: manages the delivery of data encapsulated in packets acrossnetworks.

l Network access: manages the delivery of data across local network media,regardless of the physical media type.

l Groups of protocols that are created in accordance with a protocol model arereferred to as a protocol suite. The TCP/IP protocol suite operates in accordancewith the TCP/IP reference model, and it is the predominant suite used within theInternet.

3 Application layer

l The application layer consists of many different protocols because it needs toprovide an interface between the many different application programs that may beinstalled on a device.

l The protocols in the application layer ensure that data is exchanged betweendevices using an agreed format and in an agreed manner.

l Some common application protocols and the programs they support include:l Simple Mail Transfer Protocol (SMTP): used by email programs such as Outlook

and Thunderbird when they need to send emails.l Post Office Protocol 3 (POP3): used by email programs when they need to

receive emails.l Hyper Text Transfer Protocol (HTTP): used by web browsers such as Edge and

Firefox to request and transfer webpages from the WWW.l File Transfer Protocol (FTP): often used by file sharing programs in order to

send and receive files between users across the Internet.

3 Application layer


Figure 2

4 Transport layer

l The data from multiple application layer protocols cannot just be passed on to thelower layers in a single block, as this would lead to severe delays in sending data tothe NIC.

l To visualise this problem, imagine you are heading to the till in a supermarket. Someshoppers have heavily loaded trolleys, and it takes several minutes to scan, bag andpay for all their items. Customers with fewer items use the ‘ten items or less’ queue,and although there may be more people in line, they are each served much morequickly than those in the queue for trolleys. Now imagine there is only one queue,and the customers with a few items are forced to queue alongside those with atrolley. The customers with only a few items have to wait longer to be served.

l This is exactly the same problem faced by the application layer protocols, as they allsend different sized blocks of data to the NIC. FTP may try to send a file measured inmegabytes, whereas SMTP may send an email of only a few kilobytes. If FTP gets itsdata to the NIC first, then transmission of the email is substantially delayed.

l One of the primary jobs of the transport layer is to divide all the data received fromthe application layer protocols into equal segments, which can then be mixedtogether (multiplexed) and passed to the next layer for processing. This processensures that all protocols receive an equal share of the capacity of the device’s NIC.

4 Transport layer


Figure 3

l Once the data is divided into segments it needs to be tracked so that if they aredelivered out of sequence, or some get lost, then steps can be taken to re-order orrecover them. The transport layer thus encapsulates the segments it creates with aheader, which contains sequence numbering to allow for segment tracking.

l When segments are received, they need to be placed in the correct order to recoverthe original data that was sent, but this takes time, and if your device is receivingsegments from multiple applications it can get extremely busy and may not be able tocope, leading to data loss. To prevent this, the transport layer can implement flowcontrol, which allows a device receiving segments to limit the number of segmentsthat are sent to it from a transmitting device.

l The two most common transport layer protocols of TCP/IP are Transmission ControlProtocol (TCP) and User Datagram Protocol (UDP).

l Both protocols manage the communication of multiple applications.l The differences between the two centre on the specific functions each protocol

implements.l TCP provides reliable delivery of data, therefore it supports all the functions

described above – segmentation, multiplexing, sequencing and flow control.The disadvantages of using TCP is that, due to its complexity, it can introduceunwanted delays between communicating devices.

l UDP provides rapid delivery of data, but without reliability. UDP only providessegmenting and multiplexing of data received from the application layer. Data

4 Transport layer


from communication programs using voice and video are typically intolerant ofdelay and therefore use UDP.

Figure 4

l Both TCP and UDP keep track of the application layer protocols they handle by usingport numbers, which act like doorways between the transport and application layers.These range from 1 to 65535, and protocols are associated with individual portnumbers:l SMTP: port 25l POP3: port 110l HTTP: port 80l FTP: ports 20 and 21

l How ports operate is slightly more complex than indicated above, as only serverprocesses use fixed, or well-known ports. Client processes (e.g. a web browser)using HTTP will select a random, unused port. This process will be examined in moredetail in a later module.

4 Transport layer


http://www.open.edu/openlearncreate/mod/oucontent/view.php?id=129631&section=7

5 Internet layer

l This layer allows computing devices to exchange data across networks. It receivessegments of data from the transport layer protocols and encapsulates them withinpackets. The packets contain address information identifying the source anddestination devices, allowing packet switching devices such as routers to route themto the correct destination network.

l There are two Internet layer protocols currently in use:l Internet Protocol v4 (IPv4): this is the most popular TCP/IP Internet layer

protocol, which uses 32-bit addresses, superseding historically previousversions. The networking industry is slowly phasing out IPv4 due to the rapidgrowth of the Internet and the increasing demand for IP addresses, which it canno longer support. However, this will take considerable time as there are manysystems and devices still dedicated to IPv4.

l Internet Protocol v6 (IPv6): this is the replacement for IPv4. It uses a 128-bitaddress and is capable of supporting the expected future growth of devicesconnecting to the Internet.

l The switchover from IPv4 to IPv6 was facilitated by the layered approach to networkprotocols. Because IPv6 can perform the same function as IPv4, there was norequirement to redesign the protocols above (TCP and UDP) or below the Internetlayer.

Figure 5

5 Internet layer


Activity: Compare IPv4 to IPv6As you have seen previously, bits are meaningful: the number of bits used increasesthe size of a network or the number of addresses available.

1 Go to Google and enter this search term: 2^32. (The up arrow or power symbolcan be found by pressing shift+6.) Write down the result:

Provide your answer...

2 Now search for 2^128 on Google and record the result:


3 Which number is the biggest and why?


4 What does the 'e+38' mean in 2^128?


5 What is the name of this number? (Hint: you will have to research the answer.)


6 Now try 2^128 in Wolfram Alpha.


6 Network access layer

l This layer is responsible for preparing the data packets it receives from the Internetlayer for transmission to the physical media connecting devices within the localnetwork. There are three main types of physical media available:l Copper: coaxial, twisted pair.l Optical: single mode, multi-mode.l Wireless: WiFi, satellite.

l Due the wide range of media, and supported technology, the network access layer ismore complex than the other layers. Additionally, while the upper layer protocolswithin the TCP/IP suite are implemented in software, the network access layer mustprovide physical connectivity, thus it has both hardware and software components,typically implemented within a device’s NIC.



http://www.google.co.uk/

http://www.google.co.uk/

http://www.wolframalpha.com/

l The primary functions of the network access layer are:l Accepting packets from IP and encapsulating them within frames. Different

protocols can use different types of frames.l Converting the binary bits that make up the frame into a signal suitable for the

type of media that is in use. For example, the bits are converted into anelectrical signal for copper media and into pulses of light for optical media. Bitsare converted to ultra high frequency radio waves on a wireless network.

l Whereas the upper layer protocols are controlled by the agencies charged withmaintaining the Internet (primarily the Internet Engineering Task Force), the sheernumber of physical media available has led to many different protocols beingdesigned and produced, often by commercial organisations.

Figure 6

l Over time, many of these protocols have become standardised and thus havebecome available for general use. The most commonly used network access LocalArea Network (LAN) protocol is Ethernet and its derivatives.

l The frames used by Ethernet totally encapsulate the IP packets sent from thenetwork layer, so devices cannot directly read the IP addresses they contain. Thismakes it necessary for frames to carry their own source and destination addresses toensure frames are delivered to the correct devices in the local network.

l In an Ethernet network, this address is known as a Media Access Control (MAC)address.



7 Network hardware

l A network is made up of hardware, which can be categorised as either:l transmission medial devices.

l Hardware devices make forwarding decisions to send data between user devicesacross interconnecting pathways created using copper, optical or wirelesstransmission media.

7.1 Transmission medial Most home networks use a combination of copper and wireless transmission media

to interconnect devices.l The copper wiring normally used to support the operation of Ethernet within homes is

referred to as unshielded twisted pair (UTP). This consists of four insulated twistedcopper pairs within a protective outer jacket:

Figure 7

l The advantages of using UTP in the home is that pre-made cables are easilyavailable, and they are cheaper than coaxial cables, which they have largelyreplaced.

l One disadvantage of UTP is that it is vulnerable to electromagnetic noise signals.Noise signals are created by other electromagnetic sources, such as power cables,lighting and power tools. Electromagnetic noise can appear on the UTP copper pair

7 Network hardware


and interfere with the data signals it is carrying. This can lead to data loss or datacorruption.

l To minimise the effects of noise, the copper pairs are twisted together, which helpscancel out noise signals travelling down the pair. Additionally, UTP cable lengths arelimited to 100m when carrying Ethernet to guarantee that they can support therequired data rates in the presence of noise.

l UTP cables have to be wired correctly to allow the twisted pairs to perform noisecancellation, and this is achieved using a standard plug, called an RJ45, and aparticular wiring convention. A correctly built UTP cable with an RJ45 connector canbe connected to the Ethernet NIC ports of most devices:

Figure 8

l Wireless is a very popular transmission media within home networks, as the lack ofphysical cabling makes connecting new devices relatively straightforward. In a homeenvironment, the WiFi system requires a WiFi NIC fitted to the user’s computingdevice, allowing it to connect to a compatible wireless access point (WAP), which willitself generally connect to the rest of the network using a UTP connection:

7 Network hardware


Figure 9

l WiFi is a popular network access technology as it is derived from Ethernet, and thereare many devices available that provide both Ethernet and WiFi capability. This isespecially true at home, as the ‘home router’ you use to connect to your InternetService Provider (ISP) will provide both Ethernet and WiFi connectivity, as it containsan integrated WAP.

l WiFi wireless is also affected by noise signals, but to a far greater degree than UTPas it is impossible to protect a wireless signal from external interference. WhereasUTP will guarantee a fixed data rate over 100m, the rate achieved over wireless willsteadily reduce as the user device moves away from the access point.

l WiFi introduces another serious problem, as the signal it produces does not stopwhen it reaches the limits of your property. This makes it possible for other people to

7 Network hardware


‘hijack’ your network by connecting to it wirelessly. It is therefore extremely importantto use some form of security, such as a password, to prevent such access.

7.2 Network devicesl Networks require a variety of different devices, each with a particular function, in

order to provide connectivity and data forwarding. In a home network, the routerprovided by your ISP will provide all these functions, but in larger networks withinbusinesses and schools, discrete devices are required.

7.2.1 Switches

l Switches provide connectivity points within a network, allowing you to add a largenumber of devices to a network, typically using UTP cabling. Because the mostcommon network access protocol is Ethernet, most switches will support it and arethus referred to as Ethernet switches. Ethernet switches have now largely replacedthe older and much slower Ethernet hubs.

Figure 10

l Switches provide multiple Ethernet NICs, which are referred to as ports. You can usea UTP cable to connect multiple computing devices to the ports:

7 Network hardware


Figure 11

l The term used to describe the layout of your devices is ‘network topology’. Thesimple layout shown above is referred to as a star topology, as it resembles a multi-pointed star. Note that each of the UTP cables shown must be no longer than 100m.

l The number of computing devices you can connect using a single switch is limited tothe number of ports that are available. If you need to add more devices, or you wishto extend the size of your network, you can connect two switches together. Thistopology is referred to as an extended star:

Figure 12

l The Ethernet network access protocol was originally designed to support data ratesof 10Mbps. This is too slow to support modern networks, so the protocol has evolvedto support greater data rates.

7 Network hardware


l Most Ethernet switches are capable of supporting several Ethernet variants on eachport. Although it is possible to configure each port to operate at a particular data rate,most Ethernet switches will negotiate with the connected computing device and setthemselves to the highest data rate that they both support. It is best practice toconnect switches together using the fastest data rate port available.

l Switches forward data between computers using the destination MAC addressescontained in the frames they receive. This means that switches have no knowledgeof the IP addresses of the packets contained within the frames, so they cannot beused to join together different IP networks. Referring to the diagram below, all thePCs are addressed within the same IP network and the switches will successfullyforward data between them.

Figure 13

l The diagram below shows the same topology, but this time the PCs have beenplaced in different IP networks. While the switches will forward data between the PCsbased on the MAC addresses in the Ethernet frames, the PCs will refuse tocommunicate with devices outside their own IP network.

Figure 14

7 Network hardware


Activity: Data ratesResearch the data rates supported by the following Ethernet variants:

Protocol Data rate

Ethernet 10Mbps

Fast Ethernet Provide your answer...

GigabitEthernet


10 GigabitEthernet


7.2.2 Routers

l Routers provide connectivity between different IP networks and are responsible forforwarding IP packets based on their destination IP addresses. It is the job of therouter to connect many different networks – this is how the internet operates. Routersprovide multiple Ethernet NICs, which are referred to as interfaces. Typical routersdo not have many interfaces, as they are not designed to provide connectivitybetween different IP networks rather than for individual hosts.

7 Network hardware


Figure 15

l Each router interface must be addressed with an IP address within the network towhich they connect. This IP address will act as the default gateway addressconfigured on all the host devices within the IP network:

7 Network hardware


Figure 16

l Although Ethernet is the most common network access protocol you will meet inLANs, there are many other types of protocols available, especially within Wide AreaNetworks (WANs). Because routers are designed to connect networks together, theymust be capable of supporting multiple network access protocols. Some routers arespecifically designed to connect to particular types of WANs, whereas others aremodular in design, allowing you to add the correct NIC for the WAN network accessprotocol in use.

7.2.3 Wireless Access Points (WAP)

l You can send data directly between two devices using WiFi provided that the deviceshave compatible wireless NICs fitted. This is very useful if you wish create atemporary connection between the devices, but it can prove difficult to manage asyou try to connect more devices.

l Using a wireless access point in your network provides a central WiFi connectionpoint to which all WiFi capable devices must connect in order to exchange data. Ineffect, you have created a star topology without wires:

7 Network hardware


Figure 17

l While a single star topology WiFi network can be useful, you are more likely to meetWAPs connected to Ethernet switches, allowing the network to provide both wiredand wireless network access:

7 Network hardware


Figure 18

7.2.4 Modem

l The function of a modem is to MOdulate and DEModulate data to and from atransmission media. In the early days of the Internet, computers sent binary bits,which alternated between 0 and 5v, towards an ISP using the telephone system,which was (and still is) designed to process audio signals from telephones.

l The modem was required to convert the binary electrical signal from the computerinto an audio signal suitable for transmission over the telephone system, and viceversa. So it was used to modulate data onto the phone line, and demodulate datareceived from the phone line:

7 Network hardware


Figure 19

l You will not see many individual modems in modern networks as they are nowintegrated within other devices, such as home routers. They are still needed as homeInternet access via Digital Subscriber Line (DSL) utilises the telephone system, albeitusing different frequencies. Cable Internet providers also utilise modems, as thebinary electrical signal from a computer has to be converted into the radiofrequencies used within the cable transmission system.

l There are also some legacy systems that still require modems, such as some olderchip and pin systems. Network engineers also use modems as a secret back doorinto their networks, just in case the main connection fails and they need to remotelyfind the cause of the issue.

7.2.5 Home router

l If you have an Internet connection at home, you are probably using a home routergiven to you by your service provider. Although it is often referred to as a router, it isactually a combination of all the devices that we have discussed so far:l Wireless Access Point: provides wireless connectivity for WiFi devices.l Switch: provides Ethernet ports for the connection of devices using UTP cables.l Router: provides routing between the home and ISP IP networks. Also performs

Network Address Translation (NAT) and firewall security.l Modem: converts the router output to a format suitable for transmission over the

link used to connect to the ISP, usually DSL or cable.

7 Network hardware


Figure 20

8 Network address translation

l You will have read about NAT when exploring IP packet forwarding, but it is coveredin more detail here.

l If you examine the diagram below, you will see that the home LAN is using IPaddresses in IP network 192.168.0.0/24, which will be the case for all the ISP’scustomers who are using the same type of home router. This will cause problems, asthe source and destination addresses have to be unique in every communicationunicast (sending packets between two devices).



http://www.open.edu/openlearncreate/mod/oucontent/view.php?id=129584&section=7

Figure 21

l Why do home routers use the same address on the home LAN if it will causeproblems within the Internet? Remember, IPv4 cannot provide sufficient IPaddresses for all the devices that want to use IP, so certain ranges of IP address,including 192.168.0.0/16, are set aside as private addresses.

l Private IP addresses can be used by anyone, at any time, within a private network.This addresses the issue of not having sufficient IP addresses, but creates a problemin that the IP address cannot be used to communicate over the Internet as it is notunique. However, you will have a unique, public IP address assigned to your homerouter on the interface that connects to the ISP, which in the diagram above is82.10.250.19.

l The idea of NAT is to convert the source address from all outgoing LAN packets intothe unique public address assigned to the home router, and vice versa for incomingpackets from the Internet.

IP addresses in packets

l The image below shows a packet transmitted from the home PC towards the webserver, which needs to be routed towards the Internet by the home router:



Figure 22

l Note that in the diagram above the source address is 192.168.0.101, which isprivate.

l The packet will be received by the home router, which will perform NAT, convertingthe source address to its own WAN interface IP address (82.10.250.19):

Figure 23

l The packet can now be forwarded through the Internet to the destination webserver, which will return the requested webpage in a series of packets:



Figure 24

l The IP packet is now addressed with the web server acting as the source, and thepublic address of the home router WAN interface as the destination. The homerouter will accept the incoming packet, and translate the destination address backto the private IP address of the home PC:

Figure 25

l The use of NAT and private IP addresses has extended the life of IPv4 wellbeyond what would have been possible with the original range of addresses itprovided. Private IP addresses and NAT are implemented within most home andbusiness networks.



9 Using networks securely

l You need to consider the security of your home network in order to protect yourpersonal security. If your network is not secured, or you use it in an insecure way,then you increase the risk of threats to yourself and your data.

l Consider some of the activities that you undertake via the Internet:l emailingl sending photographsl chattingl posting to wikil shoppingl banking.

l What would be the impact if someone was able to intercept any information you sentwhile doing these activities? It could range from personal embarrassment to severefinancial loss. You would probably not do any of these things with a stranger sat nextto you, but when you do them over the Internet, there is a risk that your data can beintercepted by others.

l What could be the motivation for trying to access your information? The list is long,but some popular reasons are:l general nosinessl a wish to bully or get you into troublel a wish to steal your money or datal a desire to impersonate you while carrying out a criminal activity.

l To start securing your network, consider the passwords that you use to protectaccess to your online accounts, and to your network devices such as PCs, tabletsand home routers.l Your passwords need to be strong. Use a mix of numbers, letters and special

characters. Do not use anything that could be guessed, such as a pet’s name ora birthday.

l You need to change your passwords regularly in case other people learn them.l Do not tell your passwords to anyone. Ever.l If you have set up a password hint, do not make the hint too obvious.l Do not use the same password across multiple accounts and devices. If

someone learns it, they have access to everything.l Do not write your passwords down.

l You also need to consider how your devices handle your passwords, as some will tryto be helpful and store them for you. If you are using a public computer to access awebsite that requires you to enter a password, the browser may offer to store it foryou. This is not a good idea, as the next user of the computer can access yourpasswords.

l If you log into your account and then walk off to do something else, leaving thecomputer unattended, anyone else who is present can access your account. If youleave your PC or device, logout from it first. Most PCs, tablets and smartphones can

9 Using networks securely


be configured to automatically logout after a short period of inactivity, so find out howto set this up.

10 Malware

l Malware is a type of computer program created by criminals with the intention ofstealing or damaging data and perhaps disrupting network operation. There arethree main types of malware:1 Virus: malicious software attached to another program to execute a particular

action on a computer. Viruses normally require the intervention of humans inorder to propagate themselves, and are commonly received as attachments toemails or as files stored on USB memory sticks.

2 Worms: self-contained malware programs that attack a computer and try toexploit a specific security ‘hole’ or vulnerability in a software program installedon it. Once they have successfully attacked the vulnerability, the worm copies itsprogram across the network to attack other devices on the network.

3 Trojan horse: similar in operation to a worm, except it is disguised to look like auseful software program that you may want to install on your computer. Onceyou have installed the Trojan, it will act as if it is normal software, but will besecretly carrying out some criminal activity such as logging the keys you aretyping in an attempt to copy your passwords. Trojans are normally capable oftransmitting the information they steal to interested criminals via your networkconnection to the Internet.

l There are many precautions you can take to protect yourself from malware:l Always install antivirus software on your computers and make sure it is kept up-

to-date.l Always keep your operating system updated, as updates include patches for

any vulnerabilities that may be exploited by malware. Most operating systemscan be configured to do this automatically for you.

l Never open email attachments from people you do not know. Always scan emailattachments from people you do know.

l Always scan your USB memory sticks with your antivirus software afterinserting them into your computer. Never plug in a memory stick that you have‘found’.

l Always keep copies (backups) of your important files on a separate hard drive,preferably one that is not kept connected to your network. You can then retrieveyour data if malware damages the originals.

11 Phishing

l Many criminals will try to get you to reveal passwords and other account informationby pretending to be someone else. This shouldn’t be an issue if you follow the advice

10 Malware


already covered in this course – in particular that you should never share yourpasswords. However, some criminals are very skilled, and send emails and texts thatappear to come from legitimate sources, such as a bank or a government agency:

Figure 26

l These messages will normally direct you to a website, which may appear veryconvincing but is designed to capture all your login information. To protect yourselffrom phishing, remember that legitimate organisations do not conduct sensitivebusiness via email or text – they will generally use the telephone or send a letter.When they do email, it will be a request for you to login to your account securely, sobe suspicious of any links to websites that could be run by fraudsters.

l Always check the address bar of your web browser to see which application layerprotocol is being used to send your sensitive information to a website. Responsibleorganisations will use HTTPS, which is a secure version of HTTP and can preventyour data being intercepted by Internet-based criminals:

11 Phishing


Figure 27

12 Activities

Activity: Investigating your home networkMake sure you have your parent or carer’s permission to investigate this at home. Ifyou are doing this at school, make sure you have permission from a teacher or ITTechnician.

1 What devices are wired on your LAN via UTP cable?


2 Does the cable go into an Ethernet switch or into sockets and disappear?


3 Where is the switch located?


4 How do you know if it is an Ethernet switch?

12 Activities



5 Do you have any wireless devices connected?


6 Where is the wireless access point?


7 How does your network connect to the Internet?


8 What type of WAN connection does your network have and what connectors doesit use?


9 Is there a modem and, if yes, where is it situated?


10 If at home can you find the address given to your router from the ISP? (It is calledyour ‘public’ address.)


11 How much you have learnt about networking?


Activity: Network devices and protocols – Packet TracerWe connect our devices to the Internet and the Internet connects them all together. Butwhat is the Internet made of? We say it interconnects all the devices, but how?Network devices are mainly hubs, switches or routers. There are lots of other specialistbits, but the bulk of the interconnectivity is done by switches and routers. In this courseyou have looked at client server models, web requests and emails. What do thesemessages look like and how are they sent?For each type of communication over the network there are a set of rules andspecifications as to what format and order the information is sent. These are calledprotocols and they are fundamental in understanding how the Internet works.This Packet Tracer lab explores the devices and protocols used in computer networks.You will need:

12 Activities


l Lab Book: Identify Devices and Protocols Used in Computer Networksl Packet Tracerl CASBIT.pkz

Activity: Password hintsCompanies do not store a user’s passwords in clear text – they send it through ascrambling algorithm to produce a 'hash', and the hash is then saved. The hashalgorithm does not work in reverse, so you can't unscramble a hash to get the originalpassword. When you enter your password the site uses the same algorithm to make ahash, which it then compares to the hash saved against your details.Some sites allow you to store password hints, and they save these as clear text.Adobe was hacked in 2013, and its hashed passwords and hints were stolen forthousands of customers. The hackers looked at all the hints that gave the same hash(hence were the same password). Because they had lots of hints for the samepassword it was easy to guess what they were.Can you guess the passwords used in this puzzle based on the stolen hints?

13 ResourcesFor more information, take a look at the following resources.

l Watch this computer networking tutorial to explore what is a protocol:

l For a detailed look at the complexity of what happens when you click a URL readIgor Ostrovsky’s blog post.

l Read Google's guide to online safety.l Read How-To Geek’s guide to choosing a good password and watch the following

video:

l Read Action Fraud’s guide to phishing and watch the following video:

l Watch this video on being cautious when using public WiFi:

14 End of course quizNow it’s time to test what you’ve learned in a quiz.

13 Resources


https://www.netacad.com/courses/packet-tracer-download/

https://blogs.adobe.com/conversations/2013/10/important-customer-security-announcement.html

https://zed0.co.uk/crossword/

http://igoro.com/archive/what-really-happens-when-you-navigate-to-a-url

https://www.google.com/safetycenter/everyone/start/

http://www.howtogeek.com/195430/how-to-create-a-strong-password-and-remember-it/

http://www.actionfraud.police.uk/fraud-az-phishing

15 AcknowledgementsGrateful acknowledgement is made to the following sources:Figure 1: Birmingham City University (BCU)Figure 2: Birmingham City University (BCU)Figure 3: CiscoFigure 4: Birmingham City University (BCU)Figure 5: Birmingham City University (BCU)Figure 6: CommScope. This file is licensed under the Creative Commons Attribution-Noncommercial-NoDerivatives Licencehttp://creativecommons.org/licenses/by-nc-nd/2.0/Figure 7: tlsmith1000. This file is licensed under the Creative Commons Attribution-ShareAlike Licence http://creativecommons.org/licenses/by-sa/2.0/Figure 8: Bull3t Hughes. This file is licensed under the Creative Commons Attribution-Share Alike Licence http://creativecommons.org/licenses/by-sa/2.0/Figure 9: CiscoFigure 10: Cisco/Birmingham City University (BCU)Figure 11: Cisco/Birmingham City University (BCU)Figure 12: Cisco/Birmingham City University (BCU)Figure 13: Cisco/Birmingham City University (BCU)Figure 14: Cisco/Birmingham City University (BCU)Figure 15: CiscoFigure 16: Cisco/Birmingham City University (BCU)Figure 17: Cisco/Birmingham City University (BCU)Figure 18: Cisco/Birmingham City University (BCU)Figure 19: Publisher unknownFigure 20: Cisco/BCUFigure 21: Birmingham City University (BCU)Figure 22: Birmingham City University (BCU)Figure 23: Birmingham City University (BCU)Figure 24: Birmingham City University (BCU)Figure 25: Birmingham City University (BCU)Figure 26: Publisher unknownFigure 27: Screenshot taken from Barclays, example of phishing.Every effort has been made to contact copyright holders. If any have been inadvertentlyoverlooked the publishers will be pleased to make the necessary arrangements at the firstopportunity.

15 Acknowledgements


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