What is functional composition?
- Combining two functions to get a new function
- g*f means apply f first, then g
Describe in words what map does
Applies a given function to each element of a list, returning a list of results
Describe in words what filter does
Processes a list to produce a new list containing exactly those elements that match a given condition
Describe in words what fold does
Reduces a list of values to a single value by repeatedly applying a combining function to the list values
What is a proxy server? What does it do?
- A server that sits between the network hosts and the firewall
- Packets are sent outside the network by the proxy server (on behalf of the network hosts)
- Provides anonymity, caching, and logging of user activities
What is a network topology?
The way a network and its connected devices (computers, printers, servers etc.) are connected. (eg. Star or bus)
Give three disadvantages of bus networks
- If main cable fails no network data can be transmitted
- Performance degrades heavily with increased traffic
- Security is poor as all computers on the network can see all transmissions
Give two disadvantages of star networks
- If central node goes down the whole network can’t transmit / receive data
- Can be costly to set up and install as lots of cabling is needed
What is the purpose of DHCP?
To automate the allocation of IP addresses (configuration) to hosts on a network
Why is DHCP used?
- Reduces the need for expert knowledge when configuring a host
- Reduces the time required to configure hosts
How is an IP address configured using DHCP?
- Host sends request to discover a DHCP server
- DHCP server offers configuration to host
- Host accepts configuration by echoing the accepted configuration back to the server
- DHCP server confirms that configuration has been allocated to host
What does a firewall do?
Blocks or allows network traffic, based on predefined or dynamic rules and policies
What is packet filtering?
When a firewall monitors outgoing and incoming packets and allowing them to pass or halt based on
- source and destination IP addresses
- protocols / ports
- Each packet is analysed separately
What is stateful inspection?
- When the firewall monitors the incoming and outgoing traffic from all ongoing TCP connections by:
– Analysing packet types
– Inspecting the payload
– Checking for suspicious activity (eg lots of outgoing data) - Connected packets are analysed together
How long is an IPv4 address and what is it split into?
- 32 bits/4 bytes (e.g. 192.168. 10.150)
- Network ID and Host ID
What is a subnet mask used for?
Identifying the Network ID part of an IP address (bitwise AND operation applied to subnet mask and IP address)
How long is an IPv6 address and why was it introduced?
- 128 bits (e.g. 2001:0db8:85a3:0000:0000:8a2e:0370:73)
- Introduced to ensure there would be enough addresses for all devices to have a unique one - as IPv4 addresses are running out
What is the difference between routable and non-routable IP addresses?
- Routable IP Addresses must be public addresses. They are unique on a global scale, and are allocated by a regional issuing authority.
- Non-routable IP addresses are assigned internally to devices on a private network. Many devices may have the same private address.
What is NAT?
- A process in which a router translates one or more non-routable IP addresses into one or more routable IP addresses and vice versa in order to provide Internet access to the local hosts
- A single routable IP address can be used for an entire private network
What is port forwarding?
- An application of network address translation (NAT) that redirects a communication request for the public IP address using a specific port to a pre-selected private host
- The port number is unchanged (forwarded)
What is the purpose of port forwarding?
- Allows computers outside the LAN to connect to a specific computer (and port) within the LAN
- Needed if you want to have a (web) server inside the LAN
How to determine if two computers are on the same subnet
Bitwise AND operation of subnet mask with both computer’s IP addresses. The result of the AND operations are the network IDs. These are then compared.
How does routing work?
- Routers are organised into a hierarchy
- The path to take is selected by each router, determined by the Network ID of the destination IP address
- Each router decrements the “time to live” of the packets
- Source and destination MAC addresses changed at each hop
- Network Address Translation will occur at routers at either end
Explain how a router can be configured so that a Web Server on a LAN can be accessed by computers outside the LAN
- Port forwarding
- Router must forward all traffic arriving on the HTTP(S) port to the IP address of the Web Server
