Billions of computers are linked through the Internet. And with so many devices communicating and exchanging information, each one needs to have a unique identifier so that the right information reaches the right destination.
Much as the Postal Service uses your home address to deliver the correct mail to your mailbox, computers use Internet Protocol (IP) and Media Access Control (MAC) addresses to distinguish between different devices on your network. Finding this information about your computer is simple--and it can be very useful when your machine is on a network. Here’s how to do it.

Using Windows 7

1. Click Start, All Programs, Accessories, Command Prompt.
2. In the prompt that appears, type:

Code:

ipconfig /all

and click Return.
3. The prompt will return network information for each network adapter in your computer. Find the section for the adapter that's connected to your network. For example, you can find the network information for your wireless adapter by looking under the 'Ethernet Adapter Wireless Network Connection' section.
4. To find your computer's IP address, look for the 'IPv4 Address' or 'IP Address' entry. This line will display the IP address for your system; typically it looks like a string of numbers separated by periods, such as 192.168.1.1.
5. To find your computer's MAC address, look for the 'Physical Address' entry. This line will display your adapter's MAC address, which typically looks like a string of letters and numbers separated by dashes.

Using Mac OS X

1. Click the Apple menu on the upper left part of the screen.
2. Click System Preferences. In the resulting System Preferences menu, select Network.
3. In the Network window, select the network adapter you're interested in. Your IP address will appear in the right-hand pane of the window.
4. To find your MAC address for the adapter, click the Advanced... button. Your MAC address should appear at the bottom of the window.

Nice Tutorial

Few more commands for Windows to get MAC -

To get mac addresses on the local computer

Just run the command getmac to get the mac addresses. Find an example below.

Code:

C:\>getmac

-------Output Sample [below] -------------

Physical Address    Transport Name
=================== ==========================================================
2C-3F-45-02-1B-32   \Device\Tcpip_{7E49B486-120A-4BC2-2114-B345A4D5C5}
10-13-17-BC-12-48   Media disconnected
22-B3-C5-30-76-78   \Device\Tcpip_{213E8D2A-1DBE-4240-8301-BE6F3EACAF9D}
C:\>

This command does not show mac addresses for the network connections which are disabled. You can run ncpa.cpl and check which NICs are disabled. Further, I have received comments that this command does not help identify the mac address for a specific device. For example, if I need to get the mac address for my WiFi card, output of getmac command is not helpful. We can use ipconfig command to deal with this.

Code:

C:\>ipconfig /all

-------Output Sample [below] -------------

Windows IP Configuration
   Host Name . . . . . . . . . . . . : PC-10234
   Primary Dns Suffix  . . . . . . . : mydomain.com
   
   DNS Suffix Search List. . . . . . : mydomain.com
                                       mydomain.com
Wireless LAN adapter Wireless Network Connection:
   Connection-specific DNS Suffix  . : mydomain.com
   Description . . . . . . . . . . . : Intel(R) Centrino(R) Advanced-N 6205
   Physical Address. . . . . . . . . : 3C-99-88-64-A1-F0
   
Ethernet adapter Local Area Connection:
   Connection-specific DNS Suffix  . : mydomain.com
   Description . . . . . . . . . . . : Intel(R) 82579LM Gigabit Network Connection
   Physical Address. . . . . . . . . : 73-2B-4F-D5-12-A0
  
C:\>

Get mac address of a remote computer

We can retrieve the mac addressses for a remote computer using nbtstat command.
Example:

Code:

C:\>nbtstat -a 10.63.71.55

-------Output Sample [below] -------------

Local Area Connection:
Node IpAddress: [10.59.13.47] Scope Id: []
           NetBIOS Remote Machine Name Table
       Name               Type         Status
    --------------------------------------------
    7CF71D1C3B05   <00>  UNIQUE      Registered
    MAC Address = 00-00-00-00-00-00
Wireless Network Connection:
Node IpAddress: [10.63.71.58] Scope Id: []
           NetBIOS Remote Machine Name Table
       Name               Type         Status
    --------------------------------------------
    7CF71D1C3B05   <00>  UNIQUE      Registered
    MAC Address = 7C-F7-1D-1C-3B-05
Local Area Connection 2:
Node IpAddress: [0.0.0.0] Scope Id: []
    Host not found.

Alternatively, We can run the below command to retrieve the mac addresses of a remote computer.

Code:

getmac /s remote_computer /u username /p password

remote_computer : Full name of the remote computer or IP address
username and password are of the account on the remote computer.

Example:

Code:

C:\>getmac /S remotepc.domain.com  /u administrator /p adminpassword

-------Output Sample [below] -------------

Physical Address    Transport Name
=================== ==========================================================
22-15-25-9C-3A-29   Media disconnected
34-11-45-7A-9C-48   \Device\Tcpip_{678DD7BB-675D-4E4C-E0AE-A261490EBE8C}

If you do not want to specify the password, you can skip /p parameter. You will be prompted to enter the password and the command execution will take place after that.

Errors:

Using getmac command we can retrieve the mac addresses of the machines running windows OS only. If you try this for a Linux machine you would get the error “The RPC server is unavailable.”

If you provide incorrect password, the command would fail with the error message “Logon failure: unknown user name or bad password.”