101 · Question #524
Which of the following would happen?
The correct answer is B. The PC sends an ARP looking for the MAC address of 172.17.10.4. When a PC communicates with a host on the same subnet, it sends an ARP request directly to resolve the destination IP to a MAC address before transmitting.
Question
Which of the following would happen?
Exhibit
Options
- AThe PC sends a DNS query for 172.17.10.1
- BThe PC sends an ARP looking for the MAC address of 172.17.10.4
- CThe PC sends an ARP looking for the MAC address of 172.17.10.1
- DThe PC sends a DNS query for 172.17.10.4
How the community answered
(23 responses)- B87% (20)
- C4% (1)
- D9% (2)
Why each option
When a PC communicates with a host on the same subnet, it sends an ARP request directly to resolve the destination IP to a MAC address before transmitting.
DNS resolves hostnames to IP addresses, not IP addresses to MACs - since the PC already has a numeric IP destination, no DNS query is triggered.
Because 172.17.10.4 is determined to be on the same subnet as the PC, the PC does not need to forward traffic to a gateway - it sends an ARP broadcast requesting the MAC address of 172.17.10.4 directly. Once the MAC is resolved via ARP reply, the PC encapsulates its frame using that MAC and delivers it locally without any DNS involvement.
ARP for 172.17.10.1 would occur only if 172.17.10.1 were the default gateway and the destination were on a remote subnet, not when the destination is reachable locally.
A DNS query for an IP address is not valid behavior - DNS is queried with domain names, and the PC already knows the destination IP so no lookup is needed.
Concept tested: ARP resolution for same-subnet host communication
Source: https://www.rfc-editor.org/rfc/rfc826
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