Networking Fundamentals Practice Question 10: ARP Remote Destination
Networking Fundamentals · Test 1 · question 10 of 10
A laptop is configured as 192.168.1.10/24 with default gateway 192.168.1.1, and its ARP cache is empty. The user runs ping 203.0.113.50. Before the first ICMP echo request can be sent on the Ethernet segment, what ARP request does the laptop broadcast?
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Answer:
First the laptop decides whether the destination is local. It applies its /24 mask to both addresses: 192.168.1.0 does not match 203.0.113.0, so the destination is remote and reachable only through a gateway. The IP packet stays addressed to 203.0.113.50, but the Ethernet frame has to go to the next hop, the default gateway. To build that frame the laptop needs the gateway's MAC address, so it broadcasts an ARP request for 192.168.1.1. So B is correct.
- A. ARP only resolves addresses on the directly connected network. 203.0.113.50 is not on the local segment, so no host there would answer. MAC addresses have meaning only within a single link. - C. Unicast IP traffic isn't sent to the broadcast MAC address and left for a router to pick up. The host resolves the next hop with ARP and sends a unicast frame to it. - D. ARP requests are broadcast on the local segment, not sent to the gateway. A remote host's MAC address is never learned across a router; every router rewrites the Ethernet header for the next link.
References: RFC 1122 - Requirements for Internet Hosts, section 3.3.1.1; RFC 826 - An Ethernet Address Resolution Protocol