2ping (bi-directional ping utility)

2ping is a bi-directional ping utility. It uses 3-way pings (akin to
TCP SYN, SYN/ACK, ACK) and after-the-fact state comparison between a
2ping listener and a 2ping client to determine which direction packet
loss occurs.

If you would like to quickly test 2ping against a remote listener
without setting one of your own up, there are several public test
listeners available. Try test.2ping.net, cromulent.colobox.com, or
linode-london.mirrors.finnix.org.

To run a listener, you can manually start one with e.g. "2ping --listen".
If you want to start a listener at boot, add a command like this to
/etc/rc.d/rc.local:

su nobody -s /bin/sh -c 'exec /usr/bin/2ping --quiet --listen' &> /dev/null &