icmp-tuntap

This is my final project for the course EA074 - Introduction to Computer Networks. It's a very basic implementation of the ICMP protocol over a Linux kernel TUN/TAP device. It is currently able to reply to pings (ICMP Echo Request messages) from other hosts in the network.

It currently listens to incoming bytes on the TUN/TAP interface, parses all incoming IPv4 packets (discarding the rest) and filters out the ones that carry ICMP payloads. It then decides how to reply to the incoming ICMP packets appropriately (currently sending an Echo Reply in response to Echo Request).

The program has minimal dependencies (just TUN/TAP bindings for Rust and the nom crate for implementing binary parsers) and everything is built from the ground up.

Compiling and running

You will need to install the Rust toolchain, either with rustup (recommended) or with your distro package manager. Run the run.sh:

$ ./run.sh

The script will ask for your sudo password, which I know is sketchy, but it basically does the following:

• Compile the source
• Grant NET_ADMIN capabilities to the executable, we can't create TUN/TAP interfaces without it (needs sudo)
• Assign an IP address/subnet to the TUN/TAP interface, currently 10.0.0.0/24 (needs sudo)
• Bring up the TUN/TAP interface (needs sudo)

Note that the program itself is not run with admin privileges.

In case you still get permission errors anyway, run the following:

$ ./run_sudo.sh

This will just run the executable with sudo and things will work.

Testing

You can ping an IP within the TUN/TAP subnet to verify that it responds to ICMP pings:

$ ping -I tun0 10.0.0.1

Screenshots

Here we can see that we receive, parse and reply to an ICMP Echo Request packet coming from the localhost (10.0.0.0) with destination to 10.0.0.1; the successful pings show that the ICMP/IP packets sent in reply are not malformed.

The same exchange sniffed by Wireshark: