user3313: I am new on Arduino, and I am trying to use the Ethernet shield...
but it need:

IP adress
MAC adress

IP adress is easy to get... but not MAC..
how can I get my arduino MAC adress?

user83: Arduino doesn't have a MAC address, your Ethernet adapter shield however will. The MAC address is likely printed on the interface and is constructed from 12 hexadecimal numbers, usually grouped 2 hex digits at a time.
If it isn't printed on the box or the shield, then the only way to find out is to connect it to your network, configure a valid IP address on the shield and try to connect to it (eg. ping to the address) from your PC) Then you can list MAC addresses from your PC  with arp -a.
Or when using dynamic addresses and DHCP, you can find the mac address in you DHCP server (probably your home router).
Either way, you need a sketch on your Arduino to configure an IP address.

user2881: 
Current Ethernet shields come with a sticker indicating the MAC address you should use with them.

(source)

user612: A MAC address must be unique throughout the environment in which it operates, but apart from that is largely arbitrary.  Typically the problem is solved by selling 3-octet prefixes (called OUI's) to manufacturers, who then uniquely assign the remaining 3 octets to individual device units they manufacturer.
However, if you are unable to discovery a globally unique address assigned to your device by its manufacturer, and know that its traffic will be confined to a local network, you can use a privately assigned (ie, "made up") address with the Locally Administered bit set.   An address of the form
02-xx-xx-xx-xx-xx-xx

or any other with the 2's bit of the first octet set will satisfy this criteria as long as you guarantee that it is unique in your system.
Be especially careful not to set the 1's bit of the first octet - if you do so, traffic will be marked as broadcast and so given wider distribution/attention than needed, wasting network capacity and processor time of connected devices.

3313: <p>I am new on Arduino, and I am trying to use the Ethernet shield...</p>

<p>but it need:</p>

<ul>
<li><p>IP adress</p></li>
<li><p>MAC adress</p></li>
</ul>

<p>IP adress is easy to get... but not MAC..</p>

<p>how can I get my arduino MAC adress?</p>
 83: <p>Arduino doesn't have a MAC address, your Ethernet adapter shield however will. The MAC address is likely printed on the interface and is constructed from 12 hexadecimal numbers, usually grouped 2 hex digits at a time.</p>

<p>If it isn't printed on the box or the shield, then the only way to find out is to connect it to your network, configure a valid IP address on the shield and try to connect to it (eg. ping to the address) from your PC) Then you can list MAC addresses from your PC  with <code>arp -a</code>.</p>

<p>Or when using dynamic addresses and DHCP, you can find the mac address in you DHCP server (probably your home router).</p>

<p>Either way, you need a sketch on your Arduino to configure an IP address.</p>
 2881: <blockquote>
  <p>Current Ethernet shields come with a sticker indicating the MAC address you should use with them.</p>
</blockquote>

<p>(<a href="http://arduino.cc/en/Guide/ArduinoEthernetShield" rel="nofollow">source</a>)</p>
 612: <p>A MAC address must be unique throughout the environment in which it operates, but apart from that is largely arbitrary.  Typically the problem is solved by selling 3-octet prefixes (called OUI's) to manufacturers, who then uniquely assign the remaining 3 octets to individual device units they manufacturer.</p>

<p>However, if you are unable to discovery a globally unique address assigned to your device by its manufacturer, and know that its traffic will be confined to a local network, you can use a privately assigned (ie, "made up") address with the <strong>Locally Administered</strong> bit set.   An address of the form</p>

<pre><code>02-xx-xx-xx-xx-xx-xx
</code></pre>

<p>or any other with the 2's bit of the first octet set will satisfy this criteria as long as you guarantee that it is unique in your system.</p>

<p>Be especially careful not to set the 1's bit of the first octet - if you do so, traffic will be marked as broadcast and so given wider distribution/attention than needed, wasting network capacity and processor time of connected devices.</p>
