Overview

Simple tun program to write and read data to a tun adapter

Interfaces

Assumes the following:

• Local tun adapter address is 192.168.40.1
• Destination for traffic is 192.168.40.2

Bring up Network Interface

ip link set tun0 up
ip address add 192.168.40.1/32 dev tun0
ip route add 192.168.40.2/32 dev tun0

Bring down Network Interface

ip route del 192.168.40.2/32 dev tun0
ip link set tun0 down

Routing

Enable Routing (on Linux)

Run sysctl -w net.ipv4.ip_forward=1 to temporarily enable routing Edit /etc/sysctl.conf with the line net.ipv4.ip_forward = 1 to make routing persistant across reboots

Disable Routing

Run sysctl -w net.ipv4.ip_forward=0 to temporarily enable routing Edit /etc/sysctl.conf with the line net.ipv4.ip_forward = 0 to make routing persistant across reboots

Sample programs

Echo

Simply echos back the data received by the tun to the sender but swaps the IP src and dst.

• ping 192.168.40.2 will result in a reply
  • It will keep up with a flood ping (sudo ping -f 192.168.40.2) but buffers slightly
  • Ping won't work for non-local pings due to the "dumb" echo handler. It doesn't switch the echo/reply types.
• netcat will work with UDP
  • Set up one terminal running nc -u -l 1234
  • Set up another terminal running nc -u 192.168.40.2 1234
  • You can watch messages from the second terminal show up in the first
• netcat doesn't completely work with TCP because of the "dumb" echo handler
  • Set up one terminal running nc -l 1234
  • Set up another terminal running nc 192.168.40.2 1234
  • You can watch messages from the second terminal show up in the first
  • Sending a file does not work becuase of the "dumb" echo handler

Wireshark

• You can run wireshark on the TUN adapter to see the traffic
• tcpdump or tshark will also work