Adress IEEE 8 bytes CC2530

Hi,

I know the addresses of the modules cc2530 are coded on 8 bytes.

this is an example:

00 12 4B 00 01 1F 7C 84

I know that the first three octets identify Texas Instrument: 00 12 4B

But what do others bytes mean ? In my kit, the fourth and fifth are the same always...

Thanks for your help.

Regards,

Yoann