uStack is a quick-and-dirty implementation of most common network protocols of IPv4, suitable for experiments, porting and integration of a IP network stack on embedded devices with limited resources. Currently, uStack supports a low level abstraction of a network card (using Linux TUN/TAP), Serial IP interface, Ethernet, ARP, BOOTP, IP, ICMP and UDP protocols.

The stack is easily portable to different platforms, such as the AVR and STM32 microcontrollers. The TUN/TAP driver can be replaced by real Ethernet MACs/PHYs such as the ENC28J60 chip, along with software to initialize the device and handle hardware read and write operations. Other alternatives include the use of a basic SLIP driver in one machine and a serial IP interface with the network stack on another.

Just type make ethernet to build the binary. Run it with root permissions using sudo ./ustack. A TAP interface will be created and associated with a random MAC address.

The demo application (main.c) is configured with almost all debug flags enabled by default (configured in the makefile). A static IP address / network mask is configured in the makefile. The application consists of a UDP callback routine and a loop which checks for received packets. On reception, the packet is injected into the network stack. To reach the application try this:

$ ping -c 3 172.31.69.20

PING 172.31.69.20 (172.31.69.20) 56(84) bytes of data.
64 bytes from 172.31.69.20: icmp_seq=1 ttl=64 time=0.160 ms
64 bytes from 172.31.69.20: icmp_seq=2 ttl=64 time=0.135 ms
64 bytes from 172.31.69.20: icmp_seq=3 ttl=64 time=0.139 ms

--- 172.31.69.20 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2030ms
rtt min/avg/max/mdev = 0.135/0.144/0.160/0.017 ms

Then, test the echo protocol using UDP on port 7 or the demo application on port 30168:

$ echo "hi there" | nc -u -w1 172.31.69.20 7
hi there

If you want define an IP dinamically, change the default IP, network mask and gateway addresses in the makefile to zeroes and rebuild the binary. Then, add a static ARP entry in your system defining both IP and MAC addresses (the MAC address is presented in the debug messages) and use ping with a size of 113 to configure the device:

$ sudo arp -a 172.31.69.30 -s ee:0d:78:ce:7d:4a

$ ping -c 3 -s 113 172.31.69.30

PING 172.31.69.30 (172.31.69.30) 113(141) bytes of data.
121 bytes from 172.31.69.30: icmp_seq=2 ttl=64 time=0.106 ms
121 bytes from 172.31.69.30: icmp_seq=3 ttl=64 time=0.106 ms

--- 172.31.69.30 ping statistics ---
3 packets transmitted, 2 received, 33% packet loss, time 2054ms
rtt min/avg/max/mdev = 0.106/0.106/0.106/0.000 ms

The first ping is lost, because it is used to configure the network address.

One way to run this network stack is to abstract the network interface using the Serial Line IP Protocol (SLIP). A serial cable should be used to connect both computers. To build the SLIP version, type make slip and run the network stack with ./ustack (no root priviledges are needed). On another computer, type make slip_ip to create a SLIP interface (sl0). Now you can reach the network stack using ping.