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Here is an example showing how a the MAC Address is used to generate EUI. IEEE has chosen FFFE as a reserved value which can only appear in EUI-64 generated from the an EUI-48 MAC address.
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The 16-bit 0xFFFE is then inserted between these two 24-bits for the 64-bit EUI address. The MAC address is first separated into two 24-bits, with one being OUI (Organizationally Unique Identifier) and the other being NIC specific. The IPv6 EUI-64 format address is obtained through the 48-bit MAC address. This feature is a key benefit over IPv4 as it eliminates the need of manual configuration or DHCP as in the world of IPv4. A device typically uses FE80::/64 as the prefix/prefix-length, followed by the Interface ID.Extended Unique Identifier (EUI), as per RFC2373, allows a host to assign iteslf a unique 64-Bit IP Version 6 interface identifier (EUI-64). Link-local address – A link-local prefix begins with FE80::/10.
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Global unicast address – When using SLAAC, the device receives its prefix from the ICMPv6 RA and combines it with the Interface ID.Windows XP and previous Windows operating systems used EUI-64.Īn easy way to identify that an address was more than likely created using EUI-64 is the FFFE located in the middle of the Interface ID, as shown in Figure 2.Īfter the Interface ID is established, either through the EUI-64 process or through random generation, it can be combined with an IPv6 prefix to create a global unicast address or a link-local address:
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For example, beginning with Windows Vista, Windows uses a randomly generated Interface ID instead of one created with EUI-64. Due to these concerns, a randomly generated Interface ID may be used instead.ĭepending upon the operating system, a device may use a randomly generated Interface ID instead of using the MAC address and the EUI-64 process. They are concerned that their packets can be traced to the actual physical computer. However, this has caused privacy concerns among many users. It also allows network administrators to easily track an IPv6 address to an end-device using the unique MAC address. The advantage of EUI-64 is the Ethernet MAC address can be used to determine the Interface ID. Note: The use of the U/L bit and the reasons for reversing its value are discussed in RFC 5342. The result is an EUI-64 generated Interface ID of FE99:47FF:FE75:CEE0. In this example the 0 in bit 7 is changed to a 1. Step 3: Convert the first 2 hexadecimal values of the OUI to binary and flip the U/L bit (bit 7). Step 2: Insert the hexadecimal value FFFE, which in binary is: 1111 1111 1111 1110. Step 1: Divide the MAC address between the OUI and device identifier. The EUI-64 process is illustrated in Figure 1, using R1’s GigabitEthernet MAC address of FC99:4775:CEE0. 24-bit Device Identifier from the client MAC address.The inserted 16-bit value FFFE (in hexadecimal).This means that if the 7th bit is a 0 it becomes a 1, and vice versa. 24-bit OUI from the client MAC address, but the 7th bit (the Universally/Locally (U/L) bit) is reversed.Device Identifier – The device identifier is a unique 24-bit (6 hexadecimal digits) value within a common OUI.Īn EUI-64 Interface ID is represented in binary and is made up of three parts:.Organizationally Unique Identifier (OUI) – The OUI is a 24-bit (6 hexadecimal digits) vendor code assigned by IEEE.This process uses a client’s 48-bit Ethernet MAC address, and inserts another 16 bits in the middle of the 48-bit MAC address to create a 64-bit Interface ID.Įthernet MAC addresses are usually represented in hexadecimal and are made up of two parts: IEEE defined the Extended Unique Identifier (EUI) or modified EUI-64 process.