How to Craft and Use Gratuitous ARP Packets with Netwox

Structure of Gratuitous ARP Packets

A Gratuitous ARP (ARP) packet is a special ARP request that does not expect a reply; it is sent when a host boots to announce its own IP‑to‑MAC mapping. Unlike normal ARP requests, the target IP address in a Gratuitous ARP is the sender’s own IP address.

Purpose of Gratuitous ARP

Gratuitous ARP packets serve three main purposes:

They broadcast a declaration of the host’s IP and MAC address without requiring a response.

They help detect IP address conflicts: if a reply is received, another device is already using the same IP.

They update other hosts’ ARP caches when a host’s MAC address changes, ensuring the cache reflects the new mapping.

How to Construct a Gratuitous ARP Packet

You can use Netwox module 33 to craft a Gratuitous ARP packet. The following command creates a packet with both the source and target IP set to 192.168.59.132:

root@daxueba:~# netwox 33 -g 192.168.59.132 -i 192.168.59.132

After running the command, the output confirms the packet creation. Use Wireshark to capture and verify the packet; the Info column should show “Gratuitous ARP for 192.168.59.132 (Request)”. In the ARP details, both the Sender IP address and Target IP address fields contain the same IP address 192.168.59.132.