0

I was wondering that how can all different network devices have different MAC ID's.

is it hardcoded separately for each device ? (extremely unlikely..since in production nobody would like to change the code and recompile and load the program...) or a switch is used to set the address or is it loaded from the ROM ? or something else ..

Morten Zilmer
  • 15,586
  • 3
  • 30
  • 49
Nayan Mehta
  • 31
  • 4
  • This question appears to be [off topic](http://stackoverflow.com/help/on-topic). – Jørgen R Jun 05 '15 at 08:52
  • 1
    Each manufacturer gets an [OUI](http://en.wikipedia.org/wiki/Organizationally_unique_identifier) and programs the OUI + a unique number in nvram on the device during manufacturing. (And probably some hardcodes it, and others do something else) However this is offtopic here on stackoverflow. – nos Jun 05 '15 at 08:53
  • Technically it should be unique. Practically very often it's not the case. – zerkms Jun 05 '15 at 09:00
  • @zerkms 'very often', citation? – scary_jeff Jun 05 '15 at 09:34
  • http://superuser.com/questions/268006/are-mac-addresses-unique-when-coming-out-of-the-factory – Mark Setchell Jun 05 '15 at 10:18
  • @scary_jeff it was yesterday someone in my twitter feed complaining they received a bunch of motherboards that had identical MACs. In the discussion there were even more people who confirmed they've had the similar experience in their career. – zerkms Jun 05 '15 at 11:42

1 Answers1

0

Many networking interfaces use EEPROMs that come pre-programmed with EUI-48 or EUI-64. They use EEPROMs to store configuration settings and other data anyway, so they don't have any additional cost using the pre-programmed EEPROMs other than the chips ending up slightly more expensive per 1k. Programming each device with a unique ID would however incur additional cost.

For instance, 24AA02xE is an I²C SEEPROM with pre-programmed EUI-48/EUI-64 at standard addresses. 93AA46AE48 is an SPI SEEPROM with pre-programmed EUI-48 that's directly compatible with LAN9xxx Ethernet Controllers.

I'm not affiliated with Microchip. I used their chips in a hobby project and noticed the datasheet mentioning the EUI-48 features.

FRob
  • 3,883
  • 2
  • 27
  • 40