How unique MAC ID is generated for the each card?

Question

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 ..

Answer 1

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.