CISCO EUI 64: Interface Identifier Generation For IPv6

CISCO EUI 64

The EUI-64 (Extended Unique Identifier-64) concept in IPv6 refers to a standard set of rules for forming a 64-bit interface identifier (IID) from a device’s 48-bit MAC address. This mechanism is primarily used for stateless address autoconfiguration (SLAAC), where a host dynamically learns its IPv6 prefix and calculates the remainder of its address using the EUI-64 method.

What is the Purpose EUI-64

EUI-64 was created to make IPv6 address setting and administration easier, enabling devices to connect to networks without requiring DHCP or manual address assignment. Usually divided into a 64-bit network prefix and a 64-bit local identifier, IPv6’s expansive 128-bit address space is utilized. This makes mapping the 48-bit MAC address to the 64-bit interface identifier part of an IPv6 address simple.

In IPv6, EUI-64 is an essential component of Stateless Address Autoconfiguration (SLAAC). In order to create a comprehensive, globally unique IPv6 address, devices using SLAAC combine an interface ID created by EUI-64 with a network prefix (supplied by a router).

How EUI-64 Works

A 48-bit MAC address can be changed into a 64-bit EUI-64 interface identifier in three simple steps:

Split the MAC Address: There are two 24-bit halves to the 48-bit MAC address.

• The device’s maker is identified by the Organizationally Unique Identifier (OUI), which consists of the first 24 bits.
• The Device Identifier or Network Interface Controller (NIC) specific section is made up of the final 24 bits.
• For example, if a MAC address is 00-1A-2B-3C-4D-5E, it is split into 00-1A-2B and 3C-4D-5E.

Insert FFFE in the Middle: The MAC address’s two 24-bit halves are separated by the hexadecimal value FFFE (16 bits). By doing this, the 48-bit MAC address is expanded to a 64-bit value.

• Continuing the example 00-1A-2B-3C-4D-5E, inserting FFFE results in 00-1A-2B-FF-FE-3C-4D-5E.
• FFFE was expressly selected by the IEEE as a reserved value that should only be used in EUI-64 addresses that are derived from EUI-48 MAC addresses.

Flip the 7th Bit (Universal/Local Bit): The first two hexadecimal characters, or the seventh bit from the left of the first byte, of the new 64-bit value is reversed.

• The bit is changed from 0 to 1 if it is 0, and from 1 to 0.
• We call this bit the Universal/Local (U/L) bit. It shows whether the address is administered locally or globally (universally unique).
• The seventh bit of IEEE-assigned universally unique MAC addresses is usually 0. In the EUI-64 identifier, flipping it to 1 guarantees both standard compliance and the host’s globally unique EUI-64 address.
• For example, if the first byte is 00 (binary 00000000), flipping the 7th bit (the second bit from the left in a 0-indexed byte, or the 7th bit from the left if counting from 1) changes it to binary 00000010, which is hexadecimal 02.
• As stated in RFC 4291, this change produces what is more formally known as “modified EUI-64,” however it is more often just termed EUI-64.

A 64-bit network prefix is then added to the 64-bit EUI-64 Interface ID that results from these procedures to create a full 128-bit IPv6 address.

For instance, if the IPv6 prefix is 2001:db8:abcd:1234::/64 and the final EUI-64 Interface ID is 021A:2BFF:FE3C:4D5E, the full IPv6 address becomes 2001:db8:abcd:1234:021A:2BFF:FE3C:4D5E.

Benefits of EUI-64

The benefits of EUI-64 are mostly associated with administrative efficiency, simplicity, and practical considerations:

Automatic Configuration: In many situations, the requirement for manual IP settings or DHCP is eliminated because devices can readily create globally routable addresses using their hardware address.

Globally Unique: The IPv6 address that is generated is globally unique since the interface identifier is based on the device’s distinct MAC address.

Address Harmonization: It eliminates the need to manage two distinct addresses by directly connecting IPv6 addresses and device hardware addresses, making administration easier.

Troubleshooting: The ability to easily ascertain a device’s MAC address from its IPv6 address and vice versa facilitates network troubleshooting for managers.

Disadvantages of EUI-64

Despite its advantages, EUI-64 has drawn a lot of criticism because of its security and privacy concerns:

Device Tracking: The IPv6 address contains an integrated unique MAC address that never changes. Particularly for mobile devices like laptops, cellphones, and tablets, this makes it simple to track certain devices as they switch between networks.

Privacy Leakage: A user’s device’s model, manufacturer (via the OUI), and even the approximate year of manufacture can all be discovered with the consistent, unique identity. This information might make users vulnerable to specific attacks.

Predictable Addresses: The predictability of EUI-64 generated addresses can make it easier for attackers to target particular devices and conduct network monitoring.

Violation of Layer Design:The “detail hiding” principle of network design, which aims to improve security and privacy by maintaining layer independence, is broken when a hardware address (Layer 2) is directly linked to an IP address (Layer 3).

The matching EUI-64 based IPv6 address of a device would also need to change if its hardware address changed, which is a minor worry.

Current Status and Alternatives

In recent years, EUI-64 has lost favour because of these serious privacy and security issues. Alternatives have been incorporated into numerous contemporary network technologies and operating systems:

Randomized Interface Identifiers: In place of EUI-64, randomized interface IDs are now the default on many platforms, including Microsoft Windows (since Vista). Tracking a device over time or across networks becomes significantly more difficult due to the periodic changes in these randomized addresses.

Privacy Extensions (RFC 4941): Privacy ExtensionsThe Internet Engineering Task Force (IETF) created RFC 4941, which outlines Privacy Extensions for Stateless Address Autoconfiguration in IPv6, in response to these worries. This standard suggests reducing the privacy problems associated with static IPv6 addresses connected to hardware devices by utilising short-term, randomly generated identifiers that change on a regular basis.

Examples of EUI-64 Conversion

• MAC Address: 0034:5678:9ABC
  • Split: 0034:56 and 78:9ABC
  • Insert FFFE: 0034:56FF:FE78:9ABC
  • Invert 7th bit of 00: 00 (binary 00000000) becomes 02 (binary 00000010)
  • EUI-64 IID: 0234:56FF:FE78:9ABC
• MAC Address: 0200.1111.1111
  • EUI-64 IID: 0000:11FF:FE11:1111 (after inverting the 7th bit of 02 (00000010) to 00 (00000000))
• MAC Address: 5055.4444.3333
  •  EUI-64 IID: 5255:44FF:FE44:3333 (after inverting the 7th bit of 50 (binary 01010000) to 52 (binary 01010010))

Using hardware identifiers already in place to provide unique interface IDs, EUI-64 streamlines IPv6 address management. This is particularly useful for dynamic address assignment.

Although many contexts have moved away from EUI-64, certain implementations still use it by default, such as link-local addresses on Cisco IOS devices and macOS. For network administrators, it is still crucial to comprehend EUI-64.