How can I verify which machines are turn on in single LAN from a websever?

From: GS (
Date: 10/29/05

Date: 29 Oct 2005 08:32:05 -0700


we have around 25 machiens in two floors, all are on single LAN with
single subnet, one Router provides all network related services, but we
have inernal web server for internal web site purpose. All LAN machines
gets ip address from Router using DHCP. from this web server, how can I
know which machines are on and which are off. I can ping by based on ip
addr?. the reason is, I need to backup some directories from other
Linux nachines, then I need to store all that on different external
disk. Thanks.