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Master the fundamental concepts of raw sockets through this focused micro-challenge.
Ethernet switches route by MAC address, not IP. When your host knows 192.168.1.1 is on the local subnet but not its MAC, it broadcasts an ARP request: "who has 192.168.1.1?"
| Field | Value for Request |
|---|---|
| Hardware type | 1 (Ethernet) |
| Protocol type | 0x0800 (IPv4) |
| HW addr len | 6 |
| Proto addr len | 4 |
| Opcode | 1 (request), 2 (reply) |
| Sender MAC/IP | your interface |
| Target MAC | 00:00:00:00:00:00 (unknown) |
| Target IP | 192.168.1.1 |
The Ethernet frame wraps this with destination ff:ff:ff:ff:ff:ff (broadcast), your source MAC, and EtherType 0x0806.
On Linux, AF_PACKET + SOCK_RAW lets you inject layer-2 frames directly:
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Because ARP sits below IP, you must build the Ethernet header yourself. Only the host owning the target IP unicasts a reply back to your MAC.
This task asks you to document ARP request construction with all fields printed. RFC 826 defines exactly this 28-byte layout, and the lack of authentication in ARP is why tools like arpspoof can poison caches with forged replies.
Implement a C program that documents ARP request construction.
Requirements:
Success Criteria:
Three hints are available for this task, revealed one at a time inside the code workspace so you can struggle productively before seeing them.
Every task includes starter code, theory, and hidden tests so you can implement and verify locally in the browser.
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