PING to client function is off by default. It is to reduce network load which increases with number of clients. Locating router statuses and connected devices is of course still active and monitoring runs via PING as well as the NAGIOS module.
To activate the function, just uncomment the following line in /etc/inittab:

#t1:23:respawn:/usr/local/script/ispadmin/cable_userping.pl

And then run the following command:

telinit q