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Quiz 2. Addresses, subnets, and interfaces ​

Supported Versions: Ubuntu Server 24.04 LTS (primary), Rocky Linux 9 (alternate) Last Updated: September 15, 2026

Return to lesson | Course preparation

Use the isolated two-VM lab contract. Choose an answer before opening its explanation. The examples are for interpretation, not host reconfiguration.

  1. The client sends an HTTP request directly to the server at 192.0.2.20:8080. Which description is correct?

    • A) 8080 is the server's MAC address.
    • B) Ethernet uses MAC addresses on the local link, IP identifies routed endpoints, and TCP port 8080 identifies a transport endpoint where a service must listen.
    • C) Assigning the server IP automatically starts HTTP.
    • D) TCP and UDP port 8080 always reach the same program.
Show Answer

Answer: B

Explanation: A local Ethernet frame carries an IP packet, which carries transport information and application data. Ports are protocol-specific numbers, not cables. Address configuration alone creates no listener. ICMP echo success also does not prove that TCP 8080 is open.

  1. What are the network, broadcast, and ordinary host range for 192.0.2.10/24?

    • A) Network .10, broadcast .24, hosts .1–.9.
    • B) Network 192.0.2.0, broadcast 192.0.2.255, hosts .1–.254.
    • C) Network 192.0.0.0, broadcast 192.0.255.255, hosts .0–.255.
    • D) All 256 addresses are ordinary host addresses in this lab.
Show Answer

Answer: B

Explanation: /24 reserves 24 network bits, leaving 8 host bits and 256 addresses. For this ordinary subnet, all-zero and all-one host bits identify the network and broadcast addresses, leaving 254 host addresses. /31 and /32 have special uses and should not be forced into this calculation.

  1. Which destination shares the subnet of 192.0.2.70/26, and why?

    • A) .130, because the first three octets match.
    • B) .100, because the .64/26 block spans .64–.127, with hosts .65–.126.
    • C) .20, because any documentation address is local.
    • D) .127, because a subnet's broadcast address is the recommended server address.
Show Answer

Answer: B

Explanation: /26 leaves 6 host bits, so blocks contain 64 addresses and start at .0, .64, .128, and .192. .70 and .100 belong to the second block. .130 belongs to the third. Compare the actual prefix rather than assuming every network is /24.

  1. The client has a management default route and a connected 192.0.2.0/24 route on the lab NIC. Where should a packet for .20 go?

    • A) Through the management default because default always has priority.
    • B) Directly through the lab NIC because /24 is a longer matching prefix than /0.
    • C) Through .1, which is automatically a gateway.
    • D) Nowhere until DNS is configured on the lab NIC.
Show Answer

Answer: B

Explanation: The connected route is more specific. No lab gateway or DNS is needed for same-subnet literal-IP traffic. Preserve the existing management default route. A gateway must actually exist and be reachable; an address ending in .1 is not inherently a router.

  1. Which assignment of responsibilities is correct?

    • A) DHCP forwards every packet, DNS assigns the client's MAC, and ARP resolves names.
    • B) DHCP can lease address/configuration, DNS answers name-record queries, and ARP resolves an IPv4 next-hop neighbor to a MAC on the link.
    • C) DNS success proves every service is reachable.
    • D) ARP discovers the MAC of any server across the Internet.
Show Answer

Answer: B

Explanation: For a remote IPv4 destination reached through a router, ARP normally resolves the router's local-link MAC, not the remote server's. DHCP is configuration exchange. DNS is name resolution. These answer different questions and can succeed or fail independently.

  1. Before adding an address, which evidence identifies the lab NIC reliably?

    • A) It is always eth1.
    • B) It is the second non-loopback line in ip a.
    • C) Its full MAC matches the hypervisor's recorded NIC attached to the internal-only network.
    • D) It already has the default route.
Show Answer

Answer: C

Explanation: Guest names and ordering vary. Record management and lab MACs separately for each VM and match them against ip -br link. A default route often identifies the management path, which must remain untouched. The lab NIC must also meet the no-existing-IPv4 precondition before this exercise adds an address.

  1. What does ip a do, and what can UP without LOWER_UP mean?

    • A) ip a adds an address, and UP proves Internet access.
    • B) ip a lists addresses; an administratively enabled link may still lack lower-layer carrier.
    • C) Both expressions mean that DNS works.
    • D) UNKNOWN on loopback always means the guest is broken.
Show Answer

Answer: B

Explanation: a abbreviates the address object; adding requires the add operation. Administrative enablement, carrier, address assignment, routing, and service reachability are separate observations. For missing carrier, inspect the virtual cable and network attachment before modifying IP settings.

  1. ip -4 route get 192.0.2.20 selects the lab NIC with source .10, but ping receives no replies. What has the route lookup proved?

    • A) The peer received a packet.
    • B) The kernel would select that route/source; no probe packet was sent by this lookup.
    • C) The firewall permits ICMP and TCP.
    • D) ARP has necessarily resolved the peer.
Show Answer

Answer: B

Explanation: Route selection is local evidence. After a bounded ping, inspect neighbors to distinguish unresolved local-link delivery from a path where the MAC resolves but ICMP may be filtered. Do not treat a routing decision as end-to-end success or disable a firewall to hide the symptom.

  1. After traffic, a neighbor entry has the expected peer MAC and state STALE. What does it mean?

    • A) The interface is permanently unusable.
    • B) A mapping is cached and will need reconfirmation when used; this is not immediate failure.
    • C) Someone necessarily spoofed the peer.
    • D) All neighbor entries must be flushed.
Show Answer

Answer: B

Explanation: Neighbor state changes with reachability confirmation. REACHABLE is recently confirmed, INCOMPLETE is resolving, and FAILED is failed resolution. An empty table before traffic can be normal. Compare MACs with your records and use traffic observations rather than demanding that every cached entry always read REACHABLE.

  1. A manually added address displays valid_lft forever. Will it survive reboot, and what should cleanup remove?
  • A) Yes; delete the guest's entire address table.
  • B) No persistence is implied; delete the exact successfully added IP/prefix from its identified lab NIC, and restore down only if that NIC was originally down.
  • C) Yes; only reinstalling Linux can remove it.
  • D) Delete the management default route first.
Show Answer

Answer: B

Explanation: forever means no runtime expiry timer, not saved configuration. With the lesson's empty-IPv4 precondition, removing its only lab IPv4 address also removes its automatically created connected route. If a reboot or manager already removed the address, confirm absence and skip deletion. Recover recorded variables and original state rather than guessing.

  1. You see an IPv6 address beginning fe80: on the lab NIC. Which response is appropriate?
  • A) Disable IPv6 globally to make IPv4 work.
  • B) Treat it as likely link-local, leave existing IPv6 unchanged, and continue the IPv4 exercise.
  • C) Assume Internet access because every IPv6 address is global.
  • D) Configure an IPv4 ARP entry for it.
Show Answer

Answer: B

Explanation: IPv6 has 128-bit addresses; link-local scope is limited to its link and may require an interface zone when used as a destination. IPv6 uses Neighbor Discovery rather than ARP and has no IPv4-style broadcast. A link-local address alone does not establish Internet reachability.

  1. Which completion statement is honest and complete?
  • A) “The examples were live-tested because I read the commands.”
  • B) “The lab address exists, so every TCP service works.”
  • C) “I verified the two lab NICs by MAC, addresses/routes and limited reachability evidence, preserved management, then removed only my address and restored recorded link state.”
  • D) “A host-only network is always isolated and never has DHCP.”
Show Answer

Answer: C

Explanation: The contract includes configuration, evidence, and recovery. Internal-only lab networking has no DHCP/uplink; host-only defaults must not be assumed equivalent. The examples in the lesson are illustrative, not live-test transcripts. The next lesson establishes persistent configuration without depending on leftover variables.

Revisit any uncertain result in the lesson, then continue to persistent configuration.