Ehernet shield. Doesn't like certain MAC's....weird!!

Projects Programming
1

Hi!
I have 9 devices that I'm about to finish and set up in the client's facilities.
They're basically an Arduino mega and an Ethernet Shield, plus some other modules that don't really matter.

I have developed them all at home and they work 100% over there.
I brought them to my office today and none of them wanted to boot (I was checking the DHCP server to see what IP they took). They never showed up in the "DHCP leases".
So I plugged into the console and ofund they never went beyond the "ethernet.begin(mac)" sentence.
Something, either the switch, or the DHCP server, wasn't liking my devices.
So I quickly uploaded the basic "ethernet client" sketch that comes in the IDE. It worked.... WEIRD!!
Then I tried to find differences between the code up to the .begin sentece, and there's nothing outstanding.
So I thought....maybe the MAC makes a difference...
I was using 45C2A6D03B0x being x each one of the devices
Then I changed to using DE:AD:BE:EF:FE:ED that comes in the example (removing the semicolons makes sense for what it means LOL).
Then it worked!!
So I set them all up with DEADBEEFFEEx being x each device.
Now they all work fine.
Is there a forbidden range that I just hit??? Has this ever happened to anyone?
I still don't know if it was the network switch that didn't let me go beyond, or the DHCP that didn't want to issue to my MAC...

Any "enlightment" would be appreciated...
Thanks!

2

I know it's a crazy idea, but one could try using Google...

Regards,
Ray L.

3

Well, I swear I spent hours trying to look for a reason to this, but hadn't checked the wikipedia page.
What I've found in it is that I probably shoulnd't use any made up MAC address with an even octet in the first position, is seems that the LSB bit of the first octet is reserved for multicast addresses and should not be present in the NIC itself.

I guess my office switch/router/dhcp server was rejecting these MAC's. It was fine in my house DSL router
Well at least that still leaves me a lot of MAC options, not only dead-beef-feed variants LOL

Thanks!