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When I do an arp -a scan through the cmd I don't see the other computers that are definitely part of the network at that point.

I need to be able to discover what computers are on the network because I want to use the Cain and Abel software but even that doesn't detect the IP addresses on the network.

Is there a way that the router owner can "hide" the computers on the network so they can't see each other so this prevents me from seeing other IPs. It's a network of Windows computers.

I know there's a switch called "Network Discovery" that will prevent computers from seeing each other. But is there a way around this?

Deniz
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  • If the network administrator has enabled client isolation (sometimes called "AP isolation") then clients cannot talk directly to each other. – David Schwartz Apr 08 '13 at 11:45
  • nmap is a powerful network tool that can be used in such situations. It runs on *nix systems. E.g `nmap -sP 192.168.1.0/24` will scan the whole range starting from 1 up to 254. – Valentin Bajrami Apr 08 '13 at 11:50
  • I downloaded nmap and scanned the network with the command you've given but it again only seems to show itself (the computer I am running the scan from) and the router IP, even though I have another machine right next to me that's switched on and on the network. – Deniz Apr 08 '13 at 13:13

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arp -a only shows the computers your PC has had a recent conversation with.
Do a ping to the entire LAN first (to the broadcast address), before doing the arp -a.
The ping will force a fresh conversation.
It is possible you need to do it a couple of times because your PC might miss some of the ping responses in the flood that will come back from the ping.

This is no guarantee that you will see ALL mac-addresses. Individual PC's can be configured (firewalled) to not respond to anything unless they themselves initiated the traffic.

It is possible that every computer on the LAN gets a private connection to the router and can't see anything else. (A so called virtual private vlan setup.) This is a situation that many ISPs do for their customers, but in a non-ISP scenario it is quite uncommon.
This can be done over Wifi too: That is even more unusual as it requires quite expensive access-points that support the feauture. (It's usually called "client isolation" or "AP isolation" in Wifi setups. Thanks to David who reminded me of the proper term.))

Tonny
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