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I need to find a IP address of a specific user and I only have the Mac address available, I'm using Ubuntu. Is this possible?

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5 Answers 5

up vote 5 down vote accepted

There no gaurantee that you will be able to do so, but you can try to use ARP to look up what addresses are known to the system you are on (on windows, the command is arp -g). But the arp cache expires and only systems that have "talked" to the system you are on will be displayed like this. Even then, if the machine is behind a router, you will only get the router IP address.

If you have access to the DHCP server, you may be able to look up the MAC address there and see what IP address it got. PROVIDED your network is using DHCP.

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Best sure-fire way is to access your router (most routers have a stored list of connected clients, their MACs, and corresponding IP addresses).

It's usually called a CLIENT TABLE. Also as Multiverse IT have suggested, look into the DHCP server.

Finally, arp -g, but it is not very reliable, especially if the terminal you want to identify has not connected to you in awhile.

Even better... get a network topology mapper/sniffer, such as NMAP, which I use extensively when I get deployed in strange foreign networks.

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Try scanning your local network using nmap. If your target machine is connected, a simple grep for the relevant mac address should map it to the IP address.

[root@myhost ~]# nmap -nsP 192.168.0.0/24

Starting Nmap 4.20 ( http://insecure.org ) at 2009-09-08 09:25 BST
Host 192.168.0.1 appears to be up.
MAC Address: 00:aa:bb:bb:7D:21 (Hewlett-Packard Company)
Host 192.168.0.4 appears to be up.
MAC Address: 00:aa:bb:bb:B6:64 (Dell)
Host 192.168.0.12 appears to be up.
MAC Address: 00:aa:bb:bb:8F:2E (Micro-star International CO.)
Host 192.168.0.14 appears to be up.
MAC Address: 00:aa:bb:bb:9D:1B (Tyan Computer)
Host 192.168.0.19 appears to be up.
MAC Address: 00:aa:bb:bb:91:39 (Tyan Computer)

To be pedantic, you can then ping the host then check your arp table. Say you're looking for 00:aa:bb:bb:91:39 which is shown to have the IP 192.168.0.19

[root@myhost ~] ping 192.168.0.19
[root@myhost ~] arp -n | awk '/192.168.0.19/{print $1 " - "$3}'
192.168.0.19   00:aa:bb:bb:91:39
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You could try spoofing your MAC address as the one in question. If DHCP, should trigger you to get the same address as well as creating an IP conflict. This in turn can have the person in question pop their head up wondering why they're having network trouble. Dirty way to find out, but it could work hehe.

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There are very many software products that can scan a sub-network for ARP and more.
A quick googling found these examples:
Free IP Scanner 1.6
Colasoft Mac Scanner Pro (free for non-commercial users)

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Free IP Scanner 1.6 Platform: Windows 9x/Me/NT/2000/XP/2003/Vista/7 Colasoft MAC Scanner Download URL: cmac11_build210.exe –  briealeida Nov 2 '09 at 17:04

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