CCNA Network Infrastructure and Connectivity Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  ARP resolves an IPv4 address to a MAC address

  Why this is correct

  ARP's core function is to dynamically discover the hardware (MAC) address associated with a given IPv4 address when a host must deliver a frame on the same Layer 2 segment. The host broadcasts an ARP request containing the target IPv4 address; the node that owns that address replies with its MAC address, which is then stored in the ARP cache. Without this mapping, the host cannot construct the Ethernet frame header with the correct destination MAC, making ARP a prerequisite for IPv4 communication over most LAN technologies.

• ✓

  A host may ARP for its default gateway when sending to a remote network

  Why this is correct

  When a host sends traffic to a remote network, the destination IP address is off-subnet, so the host cannot resolve that address via ARP. Instead, it encapsulates the packet with a frame whose destination MAC must be the optimal path's next hop, which is the local default gateway. The host therefore sends an ARP request for the default gateway's IPv4 address to learn that router interface's MAC address. Only after this mapping is known can the frame be transmitted onto the local link, with the destination IP still set to the remote host's address.

• ✗

  ARP is used to discover the remote router's OSPF router ID

  Why it's wrong here

  ARP is completely unrelated to the OSPF router ID, which is a 32-bit value that identifies a router within the OSPF domain. The router ID is selected administratively or derived from the highest active interface address, and it is advertised in OSPF hello packets, database descriptors, and LSAs. Discovering a neighbor's OSPF router ID happens via OSPF protocol exchange, not through any Layer 2 address resolution. ARP's scope is confined to resolving an IP address to a MAC address for local delivery, so it has no role in routing protocol elections or identifiers.

  When this WOULD be correct

  In a question about OSPF neighbor discovery on a point-to-point link, an option stating 'OSPF uses hello packets to discover neighbor router IDs' would be correct. Alternatively, if the question asked about discovering a router's OSPF router ID, the correct answer would involve show commands or OSPF processes, not ARP.

• ✗

  ARP replaces DNS for hostname resolution

  Why it's wrong here

  ARP does not replace DNS because the two protocols solve different problems in the TCP/IP stack. DNS translates human-readable hostnames like www.example.com into IPv4 or IPv6 addresses through a hierarchical system of nameservers, typically using UDP or TCP port 53. Once the host already knows the destination IP address, ARP then resolves that IP address to a MAC address for use in the data link layer frame. Thus, DNS operates at the application layer and performs name-to-IP resolution, while ARP operates at the network/data link boundary and performs IP-to-MAC resolution, making them complementary rather than interchangeable.

  When this WOULD be correct

  In a question about protocols that map hostnames to IP addresses, an option stating 'DNS replaces the need for hosts file entries' would be correct, but ARP is not involved in hostname resolution.

Option-by-option analysis

Why each answer is right or wrong

Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.

Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”