scan for machines in the subnet


I wonder what is the easiest and fastest way to detect all machines in the current subnet from one of the machines and get their MAC-adresses.

My first approach would be to ping each possible adress and then read the arp-table for valid mac's.

But assuming my limited knowledge of arp and other protocol-layers I guess there are much better ways.

I tried a broadcast-ping on the subnet (ping -b 10.21.1.0) but to my suprise it did not make all machines respond.

The more sophisticated question (and not acutally part of my task to keep tracks and logs of all machines in a WLAN-network) is if there is a way to detect machines that does not respond to ICMP-requests like ping.
One could use tools like nmap on each possible adress and every port, but this would take a lot of time.
Maybe there is a protokoll/layer (like arp?) that makes every networkcard respond to certain requests.

Any help is greatly appretiated. And excuse for possible stupid assumptions in my posting. I usually think I know a lot about networks cause I play with servers every day, but when it comes to questions that exceeed the terms "ip-adress" and "port" I realize pretty soon that in fact I know nothing.

thnx
peter



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