networks Flashcards
1
Q
Define serial transmission.
A
Serial transmission is where one bit is sent after the other down a single data line.
2
Q
Define parallel transmission.
A
Parallel data transmission is where multiple bits are sent simultaneously down several data lines.
3
Q
What are the benefits of serial over parallel transmission.
A
Cheaper = there is only one wire in single data transmission but parallel requires multiple wires so it is more expensive than serial
More reliable = Parallel experiences:
- Cross-talk: electromagnetic interference between several adjacent wires can cause bits to get corrupted (more pronounced at higher frequencies)
- Data skew: due to the slightly different properties of each wire in parallel DT, the bits travel at different speeds and arrive at different times (more pronounced at larger distances) so parallel is limited to 2 m
4
Q
Define asynchronous transmission.
A
Data is transmitted when it is available, rather than at specific intervals or according to a clock signal. This means that there can be periods of time when the transmission channel is idle.
5
Q
Define synchronous transmission.
A
In synchronous data transmission, streams of bits are transferred over a communication channel at a constant rate.
The transmitter and the receiver are synchronised using a common clock signal.
6
Q
Compare synchronous and asynchronous transmission.
A
Asynchronous
- Requires a start bit and stop bit
- Less efficient
- Used for more sporadic data like mouse clicks
Synchronous
- No start and stop bit required
- Commonly used with parallel transmission
- e.g. transmission of data across a data bus according synchronised with the clock signals
7
Q
What are the purposes of start and stop bits in asynchronous data transmission?
A
Synchronise the receiver’s clock signals to the transmitter clock
OR start the receiver’s clock ticking
8
Q
Define bit rate.
A
The rate for the number of bits transmitted across a communications channel per second.
9
Q
Define baud rate.
A
The rate for the number of times the signal changes per second.
A symbol corresponds to a set of bits that are transmitted with every signal change.
So baud rate represents the symbol rate of a channel
10
Q
Define bandwidth.
A
The range of signal frequencies that can be transmitted across a transmission medium.
11
Q
Define latency.
A
The delay from the time that a signal is sent, to the time that it is received.
12
Q
Define protocol.
A
A protocol is a set of rules that govern the communication between devices
13
Q
Define broadband.
A
A multiple data channel system in which the bandwidth of the transmission medium carries several data streams at the same time.
14
Q
Define hand-shaking protocol.
A
The sending and receiving devices exchange signals to establish that they are each ready to initiate data transfer.
15
Q
When is there a difference in bit rate and baud rate?
A
Bit rate can be higher than baud rate if more than one bit is encoded in each signal change.
16
Q
What is the relationship between bit rate and bandwidth?
A
Bit rate is directly proportional to bandwidth.
17
Q
Describe in detail the principles of a physical star topology.
A
- The central device is a switch which all devices on the network are connected to directly
- A switch uses a table that maps each device to the port it is connected to.
- In this way, the switch is able to direct messages to the correct recipient (receiving device).
- Switch is the central point of failure
- Failure in connections or workstations is isolated
18
Q
What is a logical bus topology?
A
- All nodes on the network are connected via a single backbone cable (on each end there are terminators)
- Messages are transmitted to all nodes in the network, the receivers examine the packet’s destination address and ignore it if they are not the intended recipient
- Prone to collisions as all signals travel across a single cable
- Poor security as data is transmitted to all nodes
- A break in the backbone will bring whole network to a stop
19
Q
Differentiate between physical and logical topologies.
A
A physical topology is the arrangement of wiring between devices in a network.
A logical topology is how data packets flow in a network/the architecture of communication mechanisms in a network.
20
Q
Explain peer-to-peer networking with situations it is used in.
A
- A network that has no dedicated servers.
- All computers are of equal status (same access rights) and can both share resources themselves and use resources from other computers
- Peers directly communicate with each other
- Small companies benefit as having independent computers means you don’t need an expensive server or hardware to manage and maintain
21
Q
Explain client-server networking with situations it is used in.
A
- A system in which some computers (the clients), request services provided by other computers, the servers.
- Servers are computers that provides shared resources to network users.
- Typically used in large companies where people need to access data and resources frequently
- A server can cope with multiple people accessing it
- Security and access rights are centralised
- Backup and restoration is centralised and can be managed by a specialised networks manager
22
Q
What is WiFi and its purpose?
A
- WiFi is a high-bandwidth wireless method of communication that can be used alongside or in place of wired Ethernet networks
- One of the most common wireless technologies which allows computers to connect to a network without physical connections.
23
Q
Describe a wireless network adapter as a crucial component for wireless networking.
A
It is a physical device which is required to connect to a wireless network.
It is use to convert data into a form so that it can be transmitted across the network and in a wireless network the data needs to be converted into radio waves.
(In wired it would be voltages through a wire or pulses of light through fibre)
24
Q
Describe a wireless access point as a crucial component for wireless networking.
A
- This is the bridge between wired and wireless network
- They broadcast a wireless signal which other devices can connect to, all the devices share the bandwidth of the access point.
- The Access Point is normally connected to a single wired network port.
- In the home this could be packaged with a router and a network switch, but can also be a stand alone device.
25
Outline three ways wireless networks are secured.
**1. Wireless Security Protocols**
- WEP (Wired Equivalent Privacy) - symmetric encryption algorithm, key is often too short and used for too long making it easy to decipher
- WPA (WiFi Protected Access) - larger keys, a new key is generated for each data packet
- WPA v2 - stronger encryption algorithm, message encrypted several times depending on key size
**2. Disable SSID broadcasting**
- An SSID is a string of alphanumeric characters that is specified during the setup of wireless devices to differentiate between wireless networks
- Its broadcast can be hidden so user must know the exact SSID and enter it to access the network
**3. MAC address whitelist**
- A Media Access Control (MAC) address is a string of characters that identifies a device on a network
- The router can have a whitelist of MAC addresses to allow on the network and will block any other devices
26
Describe the wireless protocol CSMA/CA steps and purpose.
CSMA/CA is a protocol used in wireless networking. It makes sure that network collisions are avoided.
1. The first step is to listen to the channel to check for the presence of any other signals.
2. Upon the detection of an existing transmission on a channel, the node that wanted to send will wait for a random period of time before trying again.
3. Once the channel is free, the data is sent.
4. Then, the sender needs to receive an acknowledgement message from the receiver to verify that the data was received successfully.
5. Otherwise, the sender will attempt to resend the message.
27
Outline RTS/CTS as part of CSMA/CA wireless protocol.
1. Once the channel is determined to be idle, a signal is sent called Request to Send (RTS).
2. The answering device then sends a Clear to Send (CTS) reply.
3. This way it knows which device asked to send first and can ensure that only that device will send its message, by not responding to further RTS signals until the original sender has finished.
28
What is the purpose of the SSID?
An SSID is a string of alphanumeric characters that is specified during the setup of wireless devices to differentiate between wireless networks
29
Define the internet
Internet is a global wide area network that is formed from the interconnection of many other networks and that uses the TCP/IP protocol.
30
Describe the structure of the internet.
- The hardware of the internet is made up of servers which hold internet web pages, cables which connect these servers together and routers/gateways to connect computers to the internet
- The main part of the internet is the backbone which consists of a set of dedicated connections that connect several large networks at various points on the globe
- These connections branch into regional networks typically controlled by ISPs
- ISPs provide access to individual end-users
31
What is the role of packet switching?
- Data transmitted is broken into small chunks (packets).
- Each packet is sent separately over a network on which other similar communications are happening simultaneously. The data is reconstructed on arrival.
- This allows for faster, more reliable and more efficient data transfer
32
What are the components of a packet?
1. Header = sender IP, recipient IP, Protocol, Packet number, TTL
2. Payload = data
3. Trailer = end of packet flag, checksum
33
Define routers, their purpose and where they are used.
A networking device that receives packets or from one host or router and uses the destination IP address that they contain to pass them correctly formatted, to another host or router.
34
Define gateways and where they are used.
A device used to connect networks using different protocols so that information can be successfully passed from one system to another.
Header is removed and reapplied with the correct format
35
Explain how routing is achieved across the internet.
1. The data is broken up into packets
2. Router examines the header to identify the destination address
3. It consults its routing table to determine the next hop (router-to-router link) for the packet
4. The routing table is constantly updated with information about the optimal route for packets to take.
36
What is the difference between WWW and the internet?
World Wide Web = A system of hypertext documents accessed via the internet using a HTTP protocol
Internet = A global network of interconnected networks using globally unique address space and uses end-to-end communications protocols
37
Define URL.
- Uniform Resource Locator
- Used to specify the means of accessing a resource and its location across a network
- protocol + domain name = URL
- This was invented so that users could use a memorable name to refer to a network and a host on that network.
38
Fully explain FQDN and domain names.
Fully Qualified Domain Name
It is a domain name that specifies its exact location in the tree hierarchy of the Domain Name System made up of host name and domain name.
www/ftp/mail = host name
bbc = domain name
com = top-level domain
39
Define IP address.
Internet Protocol Address
identifies a network or device on the internet.
40
What is the purpose of a DNS system?
A Domain Name Server accepts a Domain Name and returns the IP address associated with this Domain Name.
41
Outline a domain name lookup.
Where is raspberrypi.org?
1. Domain name query sent to recursive name server (DNS resolver)
2. Asks root name server for ORG name server IP address
3. Asks ORG name server for raspberrypi name server IP address
4. Asks raspberrypi.org authoritative name server and returns public IP address
5. DNS resolver returns address to the client
42
Explain Internet registries and their purpose.
- There are 5 global organisations with worldwide databases which hold records of domain names issued to individuals, organisations or companies.
- They allocate IP addresses to the domain names and keep a track of which domain name is associated with which IP to ensure they're unique
43
Define firewalls.
A firewall is a security feature that monitors both incoming and outgoing network traffic, preventing unauthorised access to your network.
44
Define stateful inspection as an element of firewalls.
- Examining the payload of a packet and it will be rejected if it is not part of a recognised communication.
- The firewall will keep a track of all open channels and transmissions.
- So it will know the context of each packet, i.e. which transmission and channel it is linked to.
- Any unknown source or port may be rejected.
45
Explain packet filtering as an element of firewalls.
- Examining the header of the packet against a set of rules or packet filters
- These packet filters prohibit traffic based on the packet header fields, which include source IP address, destination IP address, port number, and protocol.
- e.g. firewalls often block port 22 because SSH protocol usually uses that port; if firewall identifies packet with port number 22 in header, it will drop the packet and connection will fail
46
Describe proxy servers as an element of firewalls.
- A proxy server sits between the client devices and the firewall.
- It provides anonymity to the clients, keeping their true IP addresses hidden.
- Networks within schools often use a proxy server as a method of filtering websites for safeguarding purposes, so that young people do not inadvertently see material that is inappropriate.
47
Explain symmetric and asymmetric encryption and key exchange.
- Symmetric encryption uses the same key for both encryption and decryption.
- Symmetric encryption schemes are faster than asymmetric encryption schemes because they use less complex mathematical operations.
- They are more susceptible to risk through a man-in-the-middle attack
- Asymmetric encryption uses a related set of keys, one public and one private.
- The keys work as a pair - one key is used to encrypt the message and the other to decrypt.
- Asymmetric encryption is slower, but ensures that only the intended recipient accesses the message
- Message encrypted with recipient's public key, then decrypted with recipient's private key
48
Outline what digital signatures are and how they are used.
A digital signature can be used to authenticate the sender of a message and to guarantee the integrity of a message.
1. Sender runs a hashing algorithm on the plaintext to produce hash
2. Sender encrypts hash with private key (proves integrity of message as only sender can encrypt)
3. Bundle the digital signature with the message
4. Encrypt entire thing with recipient's public key
5. Recipient uses their private key to decrypt
6. Use sender's public key to decrypt hash
7. Runs same hashing algorithm on the plaintext
8. If same as the sender's hash, message hasn't been interfered with and verifies identity of the sender
49
Describe what a digital certificate is.
A digital certificate is an electronic document that authenticates a message sender or a website.
- A digital certificate is issued by a certification authority.
- It contains your name, a serial number, expiration dates, a copy of the certificate holder's public key, and the digital signature of the certificate-issuing authority so that a recipient can verify that the certificate is real.
- Digital certificates can be kept in registries so that authenticating users can look up other users' public keys.
50
Discuss worms and what they exploit.
- Worms have the ability to quickly replicate and distribute independently to waste resources and cause damage to the system
- They cause problems by using up network bandwidth and therefore they slow down the network significantly.
- In some cases, worms can use up all system resources, causing a denial-of-service attack.
- In a denial-of-service attack, a server will be bombarded with requests at a level that it cannot cope with.
51
Discuss trojans and what they exploit.
- A trojan is a piece of software that appears to be **legitimate** to trick the user into executing it.
- However, unbeknown to the user, it also performs malicious actions such as **data theft, redirecting search requests, installing further malware**, or **opening a “backdoor”** for **remote control** of your computer.
- The main objective of a trojan is typically to **steal confidential information** or **inflict damage.**
52
Discuss viruses and what they exploit.
- A virus is a malicious form of self-replicating software that attaches itself to other programs or files, so that it can make copies of itself and spread easily to infect computer systems.
- A virus may be designed to send spam, steal data, infect other computers on the network, or to corrupt files.
53
Describe three vulnerabilities in the computer system that can be exploited.
**Human weakness**
Users can be tricked into revealing information through social engineering techniques, can download malware by installing software, or use insecure passwords that are easily cracked.
**Out of date software**
Security issues and bugs in software can be exploited as an opportunity for a cyber attack, so patch updates are essential to fix these issues.
**Code quality**
Malware can exploit weaknesses in code. For example, if a program does not sanitise input data, a hacker could create a successful SQL injection leaving malicious instructions to exploit later on.
54
Explain how improved code quality, monitoring and protection can address worms, trojans and viruses.
**Improved code quality**
- Poorly written code might leave data in memory to be stolen or exploited later
- Or programs may contain debugging code that exposes sensitive information that the programmer forgot to remove.
- If these errors are not spotted and removed before the program is published, these vulnerabilities may be found and exploited by malware.
**Monitoring & Protection**
- Anti-malware or antivirus software is used to detect, quarantine, or remove malware such as viruses, trojans, and worms from computers.
- Anti-malware software can have a real-time checker that scans files before they are used to keep the computer safe
- Can also have scheduled scans, which perform checks upon computer files on a regular basis.
55
What can individuals do to protect against malware?
- Use anti-malware software
- Ensure software is fully up to date
- Use encryption
- Ensure sites use HTTPS
- Use passwords & PIN’s on programs and files
56
What can programmers do to protect against malware?
- Use a language with built in security features
- Use encryption for data stored
- Set access rights to appropriate parts of the system
- Thoroughly test your code, and test for known issues
- Keep knowledge up to date for threats and method to combat
57
What can system admins do to protect against malware?
- Ensure requests come from known sources
- Use firewall
- Use anti-malware
- Keep systems fully up to date
58
Describe the layers of the TCP/IP stack and their roles.
**1. Application Layer**
The application layer sits at the top of the stack and uses protocols relating to the application being used to transmit the data over a network.
- POP3
- SMTP
- HTTP/HTTPS
- FTP
**2. Transport Layer**
The transport layer uses TCP to **establish an end-to-end connection** with the recipient computer. The data is then **split into packets** and labelled with the **packet number** and the **port number** through which the packet should route.
- TCP (Transport Control Protocol)
- UDP (User Datagram Protocol) - faster data transfer but less reliable (used for real-time applications like Skype
**3. Internet Layer**
Adds the source and destination IP addresses to each packet. This combination of IP address and the port number forms a socket.
**4. Data Link Layer**
Adds the MAC Addresses identifying the Network Interface Controllers of the sender and the destination. This allows the data to get to the specific device once it has reached the required IP address.
59
What is the role of sockets in the TCP/IP stack?
A socket is an endpoint in a communication, it identifies the destination device (IP address) and application (port).
It is the IP address with a Port number
e.g.192.168.1.150 : 80
60
Define port.
- An addressable location on a network that links to a process or application.
- A port number is a way to identify a specific process to which an Internet or other network message is to be forwarded when it arrives at a server.
- The port number is a 16 bit integer
61
Describe the role of MAC addresses.
A unique 12-digit hexadecimal identifier assigned to a network interface controller to distinguish between devices on a network.
62
List the well-known ports and their purpose.
20 = FTP Data (file transfer)
21 = FTP Control (file transfer)
22 = SSH (secure remote access)
23 = Telnet (secure remote access)
25 = SMTP (mail transfer)
80 = HTTP (website access)
110 = POP (mailbox access)
143 = IMAP (mailbox access)
443 = HTTPS (secure website access)
63
What is the purpose of well-known ports?
The use of well-known ports allows client applications to easily locate the corresponding server application processes on other hosts.
64
List seven known protocols.
- FTP
- HTTP
- HTTPS
- POP3
- SMTP
- SSH
- IMAP
65
FTP
File Transfer Protocol
This allows you to download / upload files to a server, for example you would upload your websites pages to your webserver using FTP.
FTP uses port 20/21.
66
HTTP
HyperText Transfer Protocol
It is used to transfer an user to a web address that is specified via the domain.
HTTP uses port 80.
67
HTTPS
HyperText Transfer Protocol Secure
A verified, secure version of HTTP. This ensures the user that the website they are on is safe and well protected through encryption.
This uses port 443.
68
POP3
Post Office Protocol
Used to receive incoming emails from an email server. This uses port 110.
69
SMTP
Simple Mail Transfer Protocol
This is used to send emails.
SMTP uses port 25.
70
SSH
Secure Shell
- This protocol allows remote access to a computer
- This could be used to perform admin tasks on a server.
- You will only have command line access to the computer.
- SSH is also designed for operating securely over an unsecure network.
- SSH uses port 22.
71
IMAP
Internet Message Access Protocol
Protocol used by email clients to retrieve email messages from a mail server over a TCP/IP connection.
It creates copies on the local client device and synchronises any deletion on both client and server.
IMAP is port number 143
72
How is SSH used for remote access management?
- Secure Shell (SSH) can provide an encrypted connection for remote access to another computer.
- Commonly used by network admins for remote management of servers and other computers
- Secure shell tunnelling is a technique where you use the SSH port for remote access to another computer that can access ports that may be blocked on your own network's firewall
- e.g. if port 80 is blocked, use port 22 and access it through another computer
73
Explain the role of an email server.
Email servers facilitate the sending, receiving, and storage of electronic mail
74
Explain the role of a web server.
The primary role of a web server is to store, process, and deliver requested information or webpages to end users.
75
Describe IP v4 address.
- 4 octet values
- 32 bits grouped by 8 separated by decimal points
- Only supports 4.4 billion addresses
76
Describe IP v6 address.
- 8 groups of 4 hexadecimal digits
- Separated by a :
- 128 bits with alphanumeric addressing method
77
Why was IP v6 introduced?
- No more NAT (Network Address Translation)
- No more private address collisions
- True quality of service (QoS)
- Easier administration (say good-bye to DHCP)
78
What is QoS?
Quality of Service
The use of mechanisms or technologies that work on a network to control traffic and ensure the performance of critical applications with limited network capacity
79
What is a private address?
- Private IP addresses are usable only within the network they exist in.
- They are typically class C addresses, such as 192.168.x.x.
- These addresses are assigned to specific devices on a network, and the router routes traffic to it.
- Most often, these addresses are assigned by the router using DHCP and an address can only be used with one device.
- Private IP Addresses are non-routable.
80
What is a public address?
- Public IP addresses are assigned by an ISP and apply to an entire LAN.
- This is the address that other devices on the internet see and communicate with.
- Data is transferred to specific devices from the Internet using NAT and port forwarding.
- NAT occurs 'automatically' while ports can be denoted with a colon after the IP address (e.g. 255.255.255.255:99999).
- Public addresses are routable.
81
Why are non-routable (private) addresses used?
- The use of private addresses helps to overcome the overall shortage of IP addresses.
- These addresses need only be unique within the address space of the local network
- They do not need to be unique within the address space of the internet.
82
What is the purpose and function of the DHCP system?
Dynamic Host Configuration Protocol
Dynamically assigns private (non-routable) IP addresses to devices in a network.
1. Discovery = when a device is started up, it broadcasts a **discovery message** for the DHCP server
2. Offer = DHCP server **reserves an IP address** for the device and sends an **offer message** to the client (IP address, subnet mask, lease duration)
3. Request = The new client **responds** to the offer which **accepts the configuration parameters.**
4. Acknowledgement = The server responds to the DHCP request message with a **DHCP ACK** message, and it confirms the requested parameters.
83
Explain NAT and why it is used.
Network Address Translation
- When sending a packet, the header will contain a source IP and destination IP address
- However, the source IP address will be a private address (non-routable) e.g. 198.168.x.x
- So NAT converts the source IP to a public IP before transmitting the packet across the internet
- A single routable IP address can be used for an entire private network
84
Define port forwarding.
Port forwarding allows remote computers (i.e. computers on the internet) to connect to a specific computer, or service within a private local area network.
Routers can be programmed so that a request under a specific port number can be forwarded to a device with a specific IP address on the network
85
Explain why port forwarding is used.
- We can use the port number to get round the problem of only having one public IP address but wishing to offer a access to a range of internal devices.
- We can specify a different port number for each internal device
- Then create a static translation on the router to map that port to a specific internal IP addresses, and a given port.
- This static translation is called 'Port Forwarding'
86
What are the subnet masks for Class A, B and C networks?
A = 11111111 00000000 00000000 00000000 /8
B = 11111111 11111111 00000000 00000000 /16
C = 11111111 11111111 11111111 00000000 /24
87
Outline subnetting.
- Subnetting is the process of dividing one network into subdivisions of networks that are treated logically as separate networks.
- Each subnet has a different network ID
- 0 is assigned to network address and 255 for broadcast address
- Router is usually assigned to 1
88
What are the benefits of subnetting?
- Reduces the broadcast domain, improving security
- Reduces data collisions - less nodes share network address
89
Define the client-server model.
The client–server model is a paradigm where providers of resources are designated as servers, and resource requesters are designated as clients.
90
Explain the Websocket protocol, why it is used and where it is used.
A set of rules to create persistent connection between 2 devices:
1. Client sends handshaking request to establish connection
2. In response server creates a persistent full duplex (bi-directional) connection on a single socket
3. Data transferred both directions
4. Either side can close the connection
The Websocket specification defines an API to set up the connection.
91
Define API.
Application Program Interface
A set of routines enabling one program to interface with each other. The code defines how the programs work together.
92
Explain the principles of Web CRUD applications.
Data must be stored, managed and represented in the correct manner. Without the ability to manipulate your data, you essentially have a static data store that can never change.
CRUD is an acronym to explain the main processes required:
- Create
- Retrieve
- Update
- Delete
93
Describe the basic principles of REST.
Representational State Transfer
- A method of using HTTP to carry out each of the CRUD operations on a networked database.
- HTTP uses request methods which define the way in which the data will be handled.
- In HTTP you use POST (create), GET (retreive) , PUT (update), DELETE (delete) and these are mapped to the CRUD operations.
94
Explain the detailed REST model.
1. The client makes a request to the server, this will be from a web browser on the local machine.
2. The requested URL will identify the resource (ie database) and also include the query
3. The REST API is run from the server, this co-ordinates client and server applications.
4. The REST API receives XML or JSON from the database.
5. The original request and the request data are transferred using HTTP, and delivered in HTML.
95
Compare JSON and XML
**Human Readable**
- JSON = It's easy to read because it's just defining objects and values.
- XML = Less readable because it's contained within markup tags
**Compact Code**
- JSON = more compact than XML
- XML = more syntax, less compact than JSON
**Speed of Parsing**
- JSON = Quicker, because it's defined as object and value
- XML = Slower, because the data has to be extracted from tags
**Easier to create code**
- JSON = Easier, because syntax is easier
- XML = More like programming so more knowledge is needed.
**Flexibility**
- JSON = Only works with limited data types, not enough for all applications
- XML = Gives total freedom, because you can create what data types there are, so it has greater flexibility
96
Outline thin-client computing.
A network where all processing takes place in a central server; the clients are dumb terminals with little or no processing tower or local hard disk storage.
97
Outline thick-client computing.
- A thick client is the term used when a network pc that does most of its own processing for on the client itself rather than the server like a thin client.
- It also refers to the fact software is on the PC itself rather than a server.
- If the applications you are using require multimedia components or are bandwidth intensive a thick client will be much more effective.
98
Compare thin-client and thick-client computing.
**THIN-CLIENT**
- Easy to deploy requiring no extra or specialised software installations
- If the server goes down the collection of the data will go down
- Any workstation can be used on the network to do the same thing
- Reduced security threat
**THICK-CLIENT**
- Thick clients are much more expensive and require more IT work in the future
- Only requires some communication with server
- Reduced server demands
- Increased security issues
