This is a sequel to the previous post on
LED Configuration With OpenWRT,
especially the part with the YUP LED (yield uplink please,
i.e. “someone else is using the internet”).
To recap that previous post, I triggered one of the LEDs on my WRAP as
a YUP LED with ICMP echo reply packets, which results in blinking
patterns which let me read which other hosts are switched on. The ICMP
echo replies arrive as replies to the packets sent by a bunch of ping
Now I have written a new program
send-echo-request to make
the blinking pattern timing more precise and above all to avoid the
race conditions caused by the two ping processes running in parallel.
send-echo-request sends an ICMP echo request to the two
hosts which interest me, and the iptables rules then triggers the LED
with a very short 0.1s flash for a reply from one host, and a much
longer 0.4s one from the other host.
As the hosts on my local LAN reply within much less than 0.01s, the
echo replies arrive practically in the same 0.5s pulse
send-echo-request sends the echo requests in.