1.3.3 Networks Flashcards
Are the internet and the world wide web the same thing?
Explain
No
The internet is the service that allows computers to connect to each other, the world wide web is a collection of web pages stored on computers that are connected via the internet.
What is a URL?
The full address of an internet resource.
What does a URL specify?
The location of the resource on the internet
The resource name
The file type
What is the job of internet registries?
They hold records of all of the possible domain names that are in use and available for purchase.
They assign an IP address to a domain name and track which addresses are assigned to which names
Give some examples of TLDs?
.uk
.fr
.de
Give an example of some 2LDs.
.co
.sch
.gov
What does a fully qualified domain name contain?
- Host server name
- Website name
- Domain suffix
What is the difference between a fully qualified domain name and a website domain name?
A website domain name does not include the host server.
Describe the makeup of a fully qualified domain name.
[HOST].[WEBSITE NAME].[2LD].[TLD]
What does IP address stand for?
Internet protocol address
What is an IP address
A unique address that is assigned to a network device
Indicates where data has originated from and where it is to be sent
What is a wide area network?
A network of inter-connected networks spread over a large geographical area.
What do wide area networks depend on?
Third party carriers to provide connections
e.g. cable under Atlantic ocean connecting Europe and USA
What is a local area network?
A number of computers connected to each other in a close geographical area.
What can users on a local area network do?
Use connected peripherals, such as printers
Access other computers
Describe a bus topology.
All computers and peripherals are connected to a single cable.
There are terminators at either end of the cable.
What is the main advantage of a bus topology?
It is very cheap to install as only a single cable is required with no additional hardware.
What are some disadvantages of a bus topology?
- If the main cable fails, none of the computers can communicate
- If there is heavy traffic on the network, performance will degrade
- All computers on the network can see all of the data flowing - low security
Describe a star topology.
Each device on the network is connected via a central node which acts as a router to only send the correct information to the relevant computer,
What are some advantages of a star topology?
- If a cable fails, only the computer that is connected via that cable cannot communicate
- Performance does not degrade with heavy use
- No “collisions” of data
- Secure as messages are only sent to the computers which they are supposed to
- Easy to add more devices to the network
What are some disadvantages of a star topology?
- They are expensive to install as they require lots of wire and a centralised router
- If the router goes down, none of the computers can communicate
What is a physical topology?
Its actual design layout - how the system is wired
What is a logical topology?
The shape of the path that data takes as it travels through the system.
Physical and logical topologies are _____ of each other.
Independent
Give an example of how a network may use a different logical and physical topology.
It may be wired as a physical star topology but data may flow using a logical bus topology.
What is a mesh topology?
All of the computers on the network are connected to every other computer on the network.
How many nodes require a connection to the internet in a mesh network?
Only one
How do the computers in a mesh network connect to each other?
Wirelessly
What are some advantages of a mesh network?
- Reduced need for cabling - wireless
- The more nodes that are installed, the more possible routes and therefore the more redundant the network becomes
- No central point of failure
What does “self healing” mean when talking about mesh networks?
If a node goes down, the traffic is rerouted using the other nodes so the system is not affected.
What is circuit switching?
When a direct link between two devices is made for the duration of the communication and the information is sent down this path.
What is a disadvantage of circuit switching?
Because the link made stays active for the entire time, no other connections can use this link while it is in use.
What is an advantage of circuit switching?
Data arrives in the order that it is sent, meaning less processing has to happen to understand the message.
What is packet switching?
When data is split up into smaller units called packets and sent separately across a network on the fastest route available at the time. The packets are combined at the end to form the message.
What information does the payload of a packet contain?
- Actual data
- Checksum
- End of packet marker
What two main parts can a packet be split into?
Header and payload
What information does the header of a packet contain?
- Source address
- Destination address
- Packet sequence number
- Protocol
Why is the source address included in the packet header?
So that the receiver can verify that the packet is coming from the correct sender and request extra packets.
Why is the destination address included in the packer header?
So that the packet is sent to the correct receiver.
Why is the packet sequence number included in the packet header?
So that the packets can be reassembled in the correct order and that any missing packets can be identified and requested to be resent.
(would look like 4/18 for example)
Why is the protocol included in the packet header?
So that when the packets are received, they are processed in the correct way.
For example a packet with the SMTP protocol will be processed as an email, not a website.
What is the job of the checksum in a packet?
It is a hash value based on the data in the packets.
When packets are received, if the calculated hash value does not match the data in the packet it will be assumed to be corrupted and a new copy will be requested.
What does the end of packet marked do in a packet?
Denotes the end of the packet so that the computer does not read more data as the same packet.
How could the shortest route that a packet could take be calculated?
Using a path finding algorithm, such as Dijkstra’s shortest path.
What happens if a data packet does not make it to its destination?
It can be requested again
Why is packet switching so reliable?
Because if one or more routes in the network are down, there are many other routes that packets can take instead.
What is a router?
A networking device that connects two LANs, two WANs or a LAN to an ISP.
It reads the destination IP address of packets that come through it and forwards them to the recipient via the fastest path available and through many other routers.
What do packets pass through as they are sent from one direction to another?
Many routers that send the packets to more routers until it reaches its destination.
What is a “hop”?
The act of traversing between one router and another through a network.
What is a routing table?
A store of the locations of other network devices, used to calculate the shortest route for a packet to take to its destination.
Why can the routing algorithm used to decide the shortest path become a bottleneck in heavy traffic
Because the algorithms are often very complicated and therefore take time to process.
What is a network interface card?
Hardware inside a computer that sends and receives electrical signals, allowing the computer to connect to the internet.
What is a MAC address?
A unique, 48 bit identifier that is coded to the network interface card by its manufacturer to uniquely identify the device.
How is a MAC address written?
In 12 hex digits.
e.g. 00-09-5D-E3-F7-62
What is a gateway?
A network device that takes only the raw data from a packet and adds new header data in the form of a new protocol before sending the packet on its way, like a router.
What is a switch?
A network device that connects other devices which are on the network.
They send packets that have been received to the correct destination computer only.
What is a hub?
A network device that connects other devices which are on the network.
They broadcast the received data to all computers on the network and only the correct destination will accept the signal.
What is a wireless access point?
A device that outputs a WiFi signal so that devices can connect to it.
Give a pro and con of using copper cabling?
It is cheap to implement.
It is slower than fibre optics
Give a pro and con of using fibre optics?
Greater data capacity + faster
Expensive
Give a pro and con of using wireless networking?
Very flexible as user is not required to be physically connected
New security threats
What is a protocol?
A set of rules which define common methods of data communication.
Why do protocols have to be standard across all devices?
So that when data is received, it is processed in the correct way and is not misinterpreted.
What is the TCP / IP stack?
A stack of networking protocols that work together to transmit and process data across the internet.
What are the 4 layers of the TCP / IP stack?
- Application
- Transport
- Internet
- Link
What is the job of the application layer in the TCP / IP stack?
Packages data using the required protocol for the application using the data and then sends them to the transport layer.
For example if the application was a browser, it may select HTTPS as a protocol and package the data in this way.
What is the job of the transport layer in the TCP / IP stack when sending data?
Makes a connection with the recipient computer, splits the data into packets and labels them with the packet number, the total number of packets and the port through which the packet should route.
Why is the port added to the packets in the transport layer?
So that the packets are sent to the correct application on the destination computer.
e.g. port 80 is commonly used by the HTTP protocol
What does the transport layer do when receiving data?
Requests re-transmission of lost packets.
Acknowledges the receipt of packets.
What is the job of the network layer in the TCP / IP stack when sending data?
Adds the source and destination IP addresses which together with the port, form a socket.
Sends routes data from origin to destination.
What is the network layer often sometimes referred to as?
The internet layer
What layer of the TCP / IP stack to routers operate on?
The network / internet layer
What is a socket?
The complete address of where the data needs to go.
To which device and to which port on that device.
What is the job of the link layer in the TCP / IP model?
The physical connection between network nodes.
MAC addresses are added at this layer so that the data can be sent to the correct piece of hardware.
How does data move between the layers of the TCP / IP model as it is “hops” between routers?
It moves between the bottom two layers.
Data is initially given a destination IP and the MAC address of the first router to send to. When it arrives, it is given a new MAC address of the new router to send to. This continues until the destination router is reached.
How do all of the layers of the TCP / IP stack work together to send and recieve data?
- Packaged by application layer (1)
- Split into packets, numbered + port added based on application (2)
- IP addresses added to form socket (3)
- MAC address of next hardware added + sent to this device (4)
- Next router calculated from IP address (3)
- MAC address changed + sent to this device (4)
(Process continues until destination network reached) (3/4) - Data arrives on correct hardware in correct port for desired application (4)
- MAC address stripped (4)
- IP addresses removed (3)
- Port stripped (2)
- Packets reassembled in correct order (2)
- Data passed to correct application to be presented to user (1)
What does FTP stand for?
File Transfer Protocol
What is FTP?
A very efficient method of transferring data across a network.
Well suited to transferring large files for example a software update or a photographer uploading lots of photos.
What does POP stand for?
Post Office Protocol
What is POP?
When emails are retrieved from the email server, they are transferred to local storage on your device and deleted from the server.
What is a disadvantage of POP?
You can only have an email on a single device, they do not synchronise across multiple devices.
What does IMAP stand for?
Internet Message Access Protocol
What is IMAP?
When emails are retrieved from the email server, they are stored locally on the device but NOT deleted from the server.
What is an advantage of IMAP?
Emails can be synchronised across multiple devices.
What does SMTP stand for?
Simple Mail Transfer Protocol
What is SMTP?
A protocol used to transfer outgoing emails from one mail server to another or from an email client to the server when sending mail.
What is a firewall?
A hardware or software checkpoint that data must pass through in order to get into a network.
Data is checked against preconfigured rules and either accepted or rejected from the network
Give an example of how network interface cards may be used to create a firewall?
Incoming data is recieved by one NIC with another NIC connected to the internal network.
Any data that attempts to pass between these cards is analysed against packet filters.
What is packet filtering?
When packets are tested against rules to see if they will be allowed access to the network.
What are some common rules of packet filtering?
- If the source IP address is on a whitelist / blacklist
- If the port is to a port that has been blocked, such as a remote access port
- If the checksum does not match the hashed value of the packet data
What is the difference between dropping and rejecting a packet?
When a packet is dropped, it is quietly removed whereas a rejected packet causes a rejection notice to be sent back to the sender.
What is a proxy server?
A server which intercepts all of the packets entering and leaving a network, appearing as the source and destination of these packets.
This hides the actual network address of the real recipients / senders from the rest of the internet.
How can a proxy server make use of caching to speed up website access times?
It can maintain a cache of commonly visited website pages and allow the user to access them without having to retrieve them through the internet.
How many users may a proxy server serve?
Hundreds or thousands
How could a proxy server be used in a school?
Data that would be undesirable or potentially unsafe can be filtered out as it passes through the proxy in accordance with the school’s policy.
User data may be logged with their requests.
What is the similarity between a worm and a virus?
Both are malicious software that have the ability to self replicate by spreading copies of themselves.
What is the difference between a worm and a virus?
A virus requires host files to be opened in order to spread themselves whereas a worm can self replicate without any user interaction.
What do viruses do when they run in a computer?
They reside in the memory and can infect any other file that is copied into memory. Here they can cause loss or damage to data files as well as major inconvenience, such as crashes.
What do worms do when they run in a computer?
They self replicate and can send themselves to other users for example by email.
They can use up bandwidth, system memory or network resources, causing systems to slow and servers to stop responding.
Where could viruses commonly be hidden?
Inside program files, such as macros in a word document.
Where could worms commonly be hidden?
Within a data file with the user being tricked into opening the file, such as an email attachment.
What is a trojan?
Malicious code, hidden inside another file such as a game download.
Trojans do not often appear to have had any affect but open back doors in your system that the creator of the Trojan can then exploit.
What can a backdoor into your system allow other users to do?
- Access your personal information
- Use your computer power to send spam emails
What is the difference between a Trojan and viruses and worms?
Trojans cannot self replicate.
What are some common system vulnerabilities?
- Passwords (Can be guessed, found out or manipulated out of people)
- No virus protection
- Disabled firewall
- “Cracks” in software where data is passed between functions
How can computers be protected against threats?
- Encryption
- Multiple credentials + more secure credentials such as biometrics
- Firewalls
- Proxies
- Good quality code which does not overflow the buffer in memory
