Lesson 4.9.4.7

4.9.4.7 DHCP, NAT and port forwarding Quiz: AQA Computer Science, Unit 9

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 4.9.4.7, DHCP, NAT and port forwarding: 20 multiple choice questions for the AQA Computer Science (7517), Unit 9: Fundamentals of communication and networking, written with Revision Ninja.

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The 20 questions

  1. What is the main purpose of DHCP?

    • To translate domain names into IP addresses for web browsers.
    • To automatically assign IP addresses and network settings to devices on a network.
    • To send email between mail servers on different networks.
    • To encrypt the contents of messages sent between two devices.

  2. What does DHCP stand for?

    • Dynamic Hypertext Configuration Protocol
    • Dynamic Host Configuration Protocol
    • Dynamic Host Control Protocol
    • Digital Host Connection Protocol

  3. What is the first message a DHCP client sends when it joins a network?

    • DHCPOFFER, in which the server proposes an address to the client, and the client then accepts it using a further reply message.
    • DHCPDISCOVER, a broadcast asking whether any DHCP server is available.
    • DHCPACK, confirming that the server has accepted the address.
    • DHCPRELEASE, in which the client gives back its previous address.

  4. Why is NAT used in most home and small office networks?

    • It encrypts all traffic leaving the local network to the internet, so that the ISP cannot read the content of the messages sent.
    • It stores copies of web pages so that they load more quickly.
    • It gives every device a permanent public address from the ISP.
    • It lets many devices with private addresses share one public IP address.

  5. What does a NAT router do with a packet leaving a private device?

    • It discards the packet unless the destination is on the same private subnet.
    • It replaces the private source address with its public address and records the mapping in a translation table.
    • It leaves the source address unchanged and only changes the destination port.
    • It converts the packet into an email message and sends it to the ISP.

  6. What is port forwarding?

    • A process that gives each device a new port number every time it connects.
    • A method of sending a file over several ports at once to speed up transfer.
    • A rule that sends incoming connections on a given port of the public address to a chosen device inside the network.
    • A rule that stops all incoming connections to a home network by default.

  7. Why might a home user set up port forwarding?

    • To assign a permanent IP address to a laptop using DHCP.
    • To hide the home network from all external users and devices.
    • To make a web server or game server on a private device reachable from the internet.
    • To speed up downloads by splitting files across several devices.

  8. What is a DHCP lease?

    • A payment made to the ISP each month for a fixed public IP address.
    • A copy of the router's configuration stored on each connected device.
    • A reserved range of ports that a router keeps open for incoming traffic.
    • The period for which a DHCP server allows a client to keep an assigned IP address before it must renew.

  9. A home network has one public IP address shared by 3 devices. Devices 192.168.1.10 and 192.168.1.11 both browse at the same time. How does the router tell the replies apart?

    • It uses the port numbers recorded in its translation table to match each reply to the correct device.
    • It gives each device a different public IP address for the duration of the browsing.
    • It sends each reply to every device, which then discards the ones not addressed to it.
    • It uses the MAC address of the web server to decide which private device gets the reply.

  10. A games server runs on 192.168.1.50 on port 7777 and must be reachable from the internet. What should the router be configured to do?

    • Block all traffic on port 7777 and allow only outgoing connections.
    • Change the server's address to a public address using DHCP.
    • Send all incoming traffic on any port to the first device on the network.
    • Forward incoming traffic on port 7777 to 192.168.1.50 port 7777.

  11. Why does a DHCP lease need to be renewed?

    • So that the server can reclaim addresses no longer in use and keep track of which devices hold them.
    • Because the server must reset its own IP address after every lease ends.
    • Because the client must pay the ISP each time the address is renewed.
    • Because public IP addresses are changed every time a device reconnects.

  12. A device shows the self-assigned address 169.254.20.15 and cannot reach the internet. What is the most likely cause?

    • The device could not obtain an address from a DHCP server.
    • The router has used all of its port numbers for port forwarding.
    • The device is using an IPv6 address that is not supported by the router.
    • The device has been given a public address that the ISP has blocked.

  13. Which device usually performs NAT in a home network?

    • The web server hosted by the ISP.
    • The DNS server that translates domain names.
    • The home router.
    • Every individual laptop on the network.

  14. Why does NAT block unsolicited incoming connections by default?

    • No translation mapping exists for an inbound connection the internal device did not initiate.
    • Private addresses are not allowed to receive any data from the internet.
    • NAT encrypts every incoming packet, so the router cannot decode it.
    • The ISP prevents all incoming traffic on residential connections.

  15. Evaluate: which is a disadvantage of NAT?

    • It makes the internal network slower because every packet is printed first.
    • It requires every device to hold a separate public address from the ISP.
    • It prevents devices on the same local network from communicating with each other.
    • It breaks true end-to-end connectivity, so incoming connections need extra configuration such as port forwarding.

  16. A large organisation wants centrally managed addressing with few conflicts. Why is DHCP better than manual configuration here?

    • It automatically configures devices from one place, which reduces administration effort and address conflicts.
    • It removes the need for subnet masks because every host uses the same network identifier.
    • It gives every device the same public IP address, which avoids any need to route traffic.
    • It stops the network from needing a default gateway for devices to reach other networks.

  17. Which mechanism is used when a host needs a DHCP address and sends its first request as a broadcast?

    • The client uses the DHCPDISCOVER message to find available DHCP servers.
    • The client uses the ARP reply to ask the router for its public address.
    • The client uses the SMTP command to submit its address to the mail server.
    • The client uses the DNS query to find the nearest web server on the network.

  18. Which of the following is changed by NAT when a private packet leaves the network?

    • The packet's payload is always encrypted with the router's own private key.
    • The destination IP address is replaced with the address of the device that sent it.
    • The packet's protocol is changed from TCP to UDP so that it can be routed.
    • The source IP address, and usually the source port number, is replaced with the public address and a translated port.

  19. Apart from an IP address, which settings does a DHCP server typically supply to a client?

    • A MAC address, a MAC filter list and a Wi-Fi password.
    • A list of every device on the internet and the ports each one has open.
    • A subnet mask, a default gateway address and a DNS server address.
    • A public domain name and an HTTPS certificate for the router.

  20. Why does a DHCP server need to keep track of which addresses are in use?

    • So that it does not assign the same address to two devices at the same time.
    • So that it can translate every address into a domain name for browsers, and so that the browsers can find each device by its name.
    • So that it can encrypt each address using the client's MAC address.
    • So that it can charge each device a monthly fee for its address.

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