IPv6 (Interface ID)

IPv6 (interface ID)

 Interface IDs in IPv6 are used to identify hosts on a link. Interface IDs must be unique on that link.

The interface ID is 64-bit and can be set manually or automatically.

Mechanisms for uniquely setting 64-bit values ​​include the mechanisms "EUI-64" and "anonymous."

  • manual
  • Automatic (EUI-64, Anonymous)

EUI-64

 This method obtains a 64-bit interface ID based on the MAC address. Since the MAC address is a unique value, the interface ID will also be unique.

 But here comes the question, MAC addresses are 48 bits. Since the interface ID is 64 bits, it is 16 bits short.

So, to generate an interface ID with "EUI-64", form it as 64 bits with the flow below.

  • Divide the 6-byte MAC address into upper 3 bytes and lower 3 bytes, and insert "FFFE" between them.
  • Invert the lower 2nd bit (U/L bit) of the upper 1st byte.

For clarity, the diagram below shows how it is formed.

 

 For example, if the router's F0 MAC address is "000C.CE4B.B7A6" and the link-local unicast address is automatically generated in EUI-64 format, it will look like this:

MAC address: 000C.CE4B.B7A6

Divide the 6-byte MAC address into upper 3 bytes and lower 3 bytes, and insert "FFFE" between them.

"00-0C-CE" + "FF-FE" + "4B-B7-A6"

Invert the lower 2nd bit (U/L bit) of the upper 1st byte.

"00" → "02"

The interface ID is

"02-0C-CE" + "FF-FE" + "4B-B7-A6"

will be

The upper 64 bits of the link-local unicast address are "FE80::"

"FE80" + "02-0C-CE" + "FF-FE" + "4B-B7-A6"

A link-local unicast address is

FE80::20C:CEFF:FE4B:B7A6

will be

The interface ID is 64-bit and can be set manually or automatically.

anonymous address

 The "EUI-64" format requires a MAC address for the interface. Router serial interfaces do not have MAC addresses. In that case, manually setting the 64-bit interface ID is a pain!

 There is a way to automatically generate interface IDs even for interfaces without MAC addresses. It's an anonymous address. Anonymous addresses randomly generate interface IDs.

 With IPv6, there are more cases where individuals can be identified than with fixed addresses in IPv4, which raises privacy concerns. , is not user identifiable.

 This is where questions arise. Random number generation can result in the same interface ID being assigned by chance.

 However, in IPv6, when the IP address configuration is completed, it is supposed to check whether other terminals are using the same interface ID on the same link.

 There is no problem even if terminals with the same interface ID exist on other links as long as they do not overlap on the same link.

Some implementations may utilize the same interface ID as the interface with the MAC address.

Manual/automatic interface ID

 We will explain the advantages and disadvantages of manually assigning an interface ID and automatically assigning it.

 Manually assigning interface IDs to devices that are always in operation, such as servers and routers, is easier to manage. "EUI-64" based on MAC address and randomly generated "anonymous" are difficult to understand and slightly inconvenient when checking the operation of servers and routers.

 Also, if it's fixed and allocated, you're sacrificing anonymity. If the IP address participating in the global Internet is fixed for each host interface, it is convenient to get access from other hosts, but it will be easy to find out which host is the source.