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When you are connected to a wireless network or are in the office and need to diagnose a problem there are various techniques and tools to probe the network. First of all it is possible to determine from the mac address, the manufacturer of the network card in a machine. The first three bytes of the mac address is known as the OUI: the IEEE keeps a searchable public database of these. A mac address for a machine can be found using ARP. In windows the arp command can be used to query the arp cache for hosts in the network and their physical MAC addresses.

Another way of querying what machine another user is using and what is available is the NMap tool. This a fingerprinting option which probes the host in such a way as to determine what operating system the remote machine is likely to be running.

Packet sniffing is also a way that more can be discovered about the network. There is publicly available sniffer called Kismet. This software can be useful if you think that someone is piggy-backing on your network too.