Arduino/Ethernet and a MAC Address

Hello Arduino Community. So after working on a project for the past 2 months with LabVIEW connecting to Arduino over the Network, I had an epiphany. (Little knowledge of networking mind you) The MAC address is supposedly hardcoded or preprogrammed into the Eth shield by the manufacturer. There's a sticker on it telling you what the MAC address is. (just learned that today) I have been using the Ethernet libraries and in the setup you supposedly need to assign it a MAC address. I have just simply used whatever the examples had. So, right there, 2 conflicting MAC addresses. Now let's add a third. When checking the network for the IP and device, the associated MAC address for my Arduino is not even close to either the preprogrammed or the user programmed. As a matter of fact, the MAC address that actually shows up looks like complete bull...oney. 00:aa:bb:cc:de:02. However, the device name (Wiznet) is displayed. So here are the questions. First: Why on earth do we need to program the MAC address onto the Arduino? Second: Does that actually do anything? And Third: Why is my supposed pre-programmed MAC address not at all equivalent to whatever showed up in the network?

What method did you use to view the mac address?

zoomkat:
What method did you use to view the mac address?

I used the IT department. :slight_smile: I honestly couldn't tell you what he used. But he had a program that has all IPs and corresponding MAC address and device name in the entire building. And that was what showed up. I trust it mainly because it was right about my PC and it's IT.

Strange, when I load some server code with the below mac address, in my netgear router I get the bottom info.

byte mac = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };

WIZNETEFFEED DE:AD:BE:EF:FE:ED

zoomkat:
Strange, when I load some server code with the below mac address, in my netgear router I get the bottom info.

byte mac = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };

WIZNETEFFEED DE:AD:BE:EF:FE:ED

Well...that's weird. Not sure what to make of that. Cuz seriously... 00:AA:BB:CC:DE:02 looks like hacker scratch to me

Note that I'm using a w5100 based Ethernet shield.

The sticker tells you a unique MAC address you can use. The idea is that no other devices will have been assigned the same MAC address so if you use this one you can assume that it won't clash with any other devices that use an assigned MAC address. The actual MAC address used is defined by your sketch. As long as there are no other devices in the same network with the same MAC address you're using, it should work.

The MAC address 00:aa:bb:cc:de:02 does sound like an arbitrary hard-coded value but the only way I'd expect your Arduino to use that value is if your have hard-coded that value in your sketch.

If you want to confirm the info given by your IT department then I suggest you get hold of an ordinary cheap domestic unmanaged router and connect the Arduino to it, and use the router's administrative interface to see what MAC addresses it thinks are connected to it.

The MAC address is supposedly hardcoded or preprogrammed into the Eth shield by the manufacturer.

No it isn't. You specify the MAC address in your code.

If you want to confirm the info given by your IT department then I suggest you get hold of an ordinary cheap domestic unmanaged router and connect the Arduino to it, and use the router's administrative interface to see what MAC addresses it thinks are connected to it.

I shall do this thing. Thank you.