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I know the IP address of a host on my own LAN. Using that, how can I find its MAC address (without having to physically access it)?

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4 Answers

up vote 3 down vote

If you are on a Windows machine, open a command box (Start...run...cmd), PING the target machine so you have made contact with it and then issue the command arp -a to view your local arp table, which will list IP addresses and their corresponding MAC addresses eg:

C:\Users\L3K>arp -a

Interface: 192.168.200.128 --- 0xb
  Internet Address      Physical Address      Type
  192.168.200.1         00-50-7f-c3-5c-88     dynamic
  192.168.200.2         00-50-7f-d1-e1-40     dynamic
  192.168.200.6         00-80-77-dd-a8-6b     dynamic

If you are on a linux-based system, install the arp-scan utility and then from a command line you can ask for a scan of your network - in my case:

arp-scan 192.168.200.0/24
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up vote 0 down vote

As long as there is no gateway routing the traffic between the computers, any sniffer would give you this information.

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Thanks for the answer Ofir. As a sub-question, is there a way of doing this if the host in question is down? Yes, I could query my own host's ARP cache, but it unfortunately doesn't currently contain the IP I'm interested in. So I was wondering if there's a way to somehow extract say an intermediary router's ARP cache and look up in that? – Frederick Sep 15 '10 at 8:20
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up vote 0 down vote

You can always consult the arp table on your router (in some cases, the router combines the arp and dhcp lease tables together).

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Exactly what I'm looking for, but what tools or commands will help me do that? – Frederick Sep 15 '10 at 8:22
But wait a minute, I am on the same LAN, so there won't be any router right? – Frederick Sep 15 '10 at 8:25
Typical LANs will have at least one router. Depending on the router, you have different options of how to get it. Most home routers you need to access it using the Web Interface in order to find that information, more complex routers will let you telnet in or query via the console port in order to get that information. – MaQleod Sep 15 '10 at 8:31
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up vote -1 down vote

If you have a managed switch or your router lets you view its ARP table you can get this from there.

If the computer you have the IP for is online you can ping it and get its MAC from you local ARP table.

A general note for the sake of others: it is not possible to obtain the MAC address for machines that are on a different LAN since Layer 3 protocols are used for addressing and delivery in this case and MAC is Layer 2.

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Didn't really give him any instructions on "how" to do this. – GregD Feb 13 '11 at 14:03
In the case of viewing it on the router, you just go to the web interface and hunt around. Can't be much more specific than that since every router has a different layout and set of pages for its web admin. Seems like a harsh -1 to me, especially since I gave more info than MaQleod. – imoatama Jul 29 '11 at 14:23
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