Network Stack

Implentation of TCP handshakes from ethernet frames.

The original idea for this project was to implement a simple toy web server as inspired by this, however, things got away from me and it became something much more than just a HTTP server.

The ultimate goal is still to have this stack ping google.com or example.com on port 80 (so no SSL). See To be implemented for a list of things that still need to be implemented for this to happen.

Features

• Implementation of IEEE 802.3 ethernet frame parsing
• ARP
• IPv4
• ICMP
• TCP SYN-SYN/ACK handshake

Setup

Setup virtual network interface:

Setup a Linux TAP device to access L2 data. Bring up the TAP device like so:

# largely taken from this post: https://stackoverflow.com/questions/1003684/how-to-interface-with-the-linux-tun-driver

ip addr show # my eth0 inet address is 10.0.2.15/24 as Im running on a VirtualBox vm with Ubuntu 18.04 guest
sudo ip tuntap add mode tap dev tun0 # make sure the mode is tap and not tun!
sudo ip addr add 10.0.3.0/24 dev tun0  # give it an address (that does not conflict with existing IP)
sudo ip link set dev tun0 up  # bring the if up
ip route get 10.0.3.50  # check that packets to 10.0.3.x are going through tun0
# 10.0.3.50 dev tun0 src 10.0.3.0 uid 1000 
ping 10.0.3.50 # leave this running in another shell to be able to see the effect of the next example, nobody is responding to the ping

C include path:

${workspaceFolder}/**
/usr/include/x86_64-linux-gnu
${workspaceFolder}/include
/usr/include
/usr/lib/gcc/x86_64-linux-gnu/13/include

Compile:

make

The compiled binary is /bin/main

Execution:

Check src/main.c for segmented tests.

Configuring ARPing updates kernel ARP Table

Replace <tuntap IF name> with your IF name (tun0, tap0, etc)

sudo bash -c 'echo 1 > /proc/sys/net/ipv4/conf/<tuntap IF name>/arp_accept'

See: https://www.spinics.net/lists/netdev/msg314093.html & https://askubuntu.com/questions/783017/bash-proc-sys-net-ipv4-ip-forward-permission-denied

Debugging

tcpdump -i <tun/tap name> <specify protocol, leave empty for everything> -v

With the above running, go to another terminal and run your command.

To be implemented

• Full TCP RFC
• Sockets API
• Some sort of HTTP client (ex: a simple curl like tool that can send GET requests) - currently not planning to implement POST and the other HTTP requests.

References

• Main inspiration & significant parts of the implementation from saminiir's Level-IP.
  • Associated blog posts:
    • https://www.saminiir.com/lets-code-tcp-ip-stack-1-ethernet-arp
    • https://www.saminiir.com/lets-code-tcp-ip-stack-2-ipv4-icmpv4/#internet-protocol-version-4
    • https://www.saminiir.com/lets-code-tcp-ip-stack-3-tcp-handshake/
• General context for the network stack / OSI model from RFC 1180 & TCP-IP Model article.
• Some other general context resources:
  • https://users.rust-lang.org/t/implementing-my-own-tcp-stack/96759/3
  • https://www.youtube.com/watch?v=bzja9fQWzdA&list=PLqbS7AVVErFivDY3iKAQk3_VAm8SXwt1X
• Specifics for each function in resources.md and each individual source & header files.