Extended Unique Identifier-64 or simply "EUI-64" is a key element and has become a pivotal standard in modern networking, primarily used for generating Interface Identifiers in IPv6 addressing. One distinct operation in the EUI-64 generation process involves inverting the 7th bit of the 48-bit MAC address. This operation has been widely adopted, but the underlying reasons for this specific manipulation are not always well-understood. I explain the reason behind this specific manipulation, shedding light on the significance and implications of inverting the 7th bit in EUI-64.
The practice of inverting the 7th bit in EUI-64 can be traced back to the development of IPv6. When IPv6 was designed, there was a deliberate decision to differentiate between locally administered and globally unique MAC addresses. The 7th bit in a MAC address is known as the Universal/Local (U/L) bit, which indicates whether the address is globally administered or locally administered. When this bit is set to '0' the address is considered globally unique, and when it is set to '1' it signifies a locally administered address.
Inverting the 7th bit (U/L bit) ensures that the resulting identifiers are appropriately designated for local significance, avoiding conflicts with globally administered addresses and allowing for efficient local network configuration. Understanding the rationale behind this bit inversion is vital for network administrators and engineers, as it plays a pivotal role in the successful implementation of IPv6 in modern networking environments.
