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Networking Fundamentals · Intermediate

Interface Identifier (IID)

The host portion of an IPv6 address, normally the last 64 bits.

Definition

The interface ID can be configured manually, derived from the MAC address with modified EUI-64, generated randomly (RFC 7217 stable privacy addresses or RFC 8981 temporary addresses), or assigned by DHCPv6. Current operating systems default to random identifiers to protect privacy.

Example

In 2001:db8:1:1::25, the interface ID is ::25 (0000:0000:0000:0025).

Exam tip

EUI-64 IIDs reveal the MAC address, which is why modern OSes use random IIDs.

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