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Consequences of using invalid mac


#1

Hi.

I found Jay Jays mac address generator where he sets the last two bits on the first byte to 01 which means that the mac address is UNICAST and locally administered. I’m just curious of what the consequences could be (if the device is used behind a local router) if these are not set to this. Could the router reject the dhcp request for instance?

Mac address generator: https://www.ghielectronics.com/community/codeshare/entry/822
More info: http://packetsdropped.wordpress.com/2011/01/13/mac-address-universally-or-locally-administered-bit-and-individualgroup-bit/


#2

I think one thing is that some routers wont give you a IP address when DHCP is used.
For static IP there is no known issue as far as I know.


#3

I keep running into problems when I forget to set a MAC address after resetting the firmware (which I have to do more often than I like).

The default MAC address for all GHI devices (at least G120 & G400) is the same and when you have more of them in the same net, they start to confuse the routers.

Package routes through the net will become a lottery, regardless of using DHCP or static IPs.

I personally would like to see a unique MAC on every device. A way to reliably generating one based on processor SN or something would also OK.


#4

@ Peter B - An option that i have in mind is to use the E2PROM memory on G120 to store a generated MAC… This memory is left untouched after reflashing the firmware. A small piece startup code could check and set the MAC address if neccesary.


#5

@ RobvanSchelven

We are using an EEPROM with an factory written unique EUI-48 adress so we use this id as our mac address and unique identifier of the device.


#6

@ olif - That is a good option!


#7

Thanks for those ideas. I think I will implement it when I find the time.