Cannot ping Android devices on same wifi network
I know this question is quite old now, but I came across this looking to for an answer and managed to work it out myself.
What I did was download a root file explorer (I used Root Browser from JRummy Apps) and navigate to /proc/sys/net/ipv4 edit icmp_echo_ignore_all so that it is a 1-line, 1-character file that simply says 0 (when I opened the file, it was set to 1)
No reboot, ICMP requests started working upon saving. Hope that helps someone else!