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Gratuitous ARP

Gratuitous ARP implementation written in C to mess local networks.

Usage

$> garp eth0 192.168.1.42

This will send a Gratuitous ARP on eth0 interface saying that your IP address is 192.168.1.42. As a broadcast packet, it will say to other machines in the local area network that you is responsible for answering for that IP.

Compilation

We use cmake to compile project. Refer to project root directory and execute:

$> mkdir build
$> cd build
$> cmake ..
$> make

This will generate the binary file garp

This project only compiles on Linux based systems.

Address Resolution Protocol - ARP

ARP protocol maps layer 3 addresses to layer 2 addresses. A layer 3 address could be IP (IPv4) and a layer 2 address could be Ethernet (MAC address). ARP enables a host to know which other host (MAC address) respondes to a given IP on a local area network. Also the inverse operation. As a request and response protocol, the following image shows its base workflow:

Basic ARP protocol workflow - Gratuitous ARP project

As could be seen, left host sends a ARP request asking for which is the MAC address (host) that responds to IPv4 10.0.0.5. Then, right host gives the ARP response answering the question. Each host updates its own ARP Table.

Contributing

Just fork, modify and send a pull request.