Mobile Node Identifier Option for Mobile IPv6 (MIPv6)
Extracted elements (12)
The identifier option is only needed on the first registration at the home agent; subsequent registrations can use the home address. This design reduces the window of privacy vulnerability compared to always exposing the identifier.
The option uses a Subtype field to allow multiple identifier types within a single option type, anticipating that additional identifier types (beyond NAI) will be defined in the future without requiring new option type allocations.
The Mobile Node Identifier option is part of a solution enabling dynamic home address allocation in MIPv6. This complements RFC 3775, which uses only IPv6 home addresses for identification, by allowing AAA infrastructure, HLR/AuC, or application-specific identifiers to be used instead.
The MN-NAI mobility option MUST be implemented by all entities implementing this specification.
The Mobile Node Identifier option SHOULD be used when IKE/IPsec is not used for protecting binding updates or binding acknowledgements. It is typically used with the authentication option [RFC4285] but may also be used independently.
When present, the Mobile Node Identifier option MUST appear before any authentication-related option in a message containing a Mobility header.
The MN-NAI option reveals the home affiliation of a user, potentially assisting attackers in determining user identity, targeting specific victims, or probing the username space. Mitigations include link-layer encryption, IPsec, or use of privacy NAIs and temporary pseudonyms as identifiers.
The MN-NAI Mobility Option uses subtype value 1 and identifies the mobile node using an identifier of the form user@realm as defined in RFC 4282. This subtype MUST be implemented by entities implementing this specification.
The Mobile Node Identifier option is a new optional data field carried in Mobile IPv6 messages that include a Mobility header. It contains an Option Type (8-bit, value 8), Option Length (8-bit, length of Subtype and Identifier fields), a Subtype field (8-bit, specifying the identifier type), and a variable-length Identifier field.
IANA assigned the value 8 for the MN-ID-OPTION-TYPE in the Mobile IPv6 numbering space. A new namespace was created for the subtype field of the Mobile Node Identifier option; NAI (subtype 1) is the currently allocated value. New values require Standards Action per RFC 2434.
The use of a permanent, stable identifier in the Mobile Node Identifier option may compromise user privacy by making it possible to track a particular device or user across different locations. The vulnerabilities are similar to those already present in Mobile IPv6's Home Address option.
The Mobile Node Identifier option encoding: Option Type is 1 octet (value 8), Option Length is 1 octet representing the length of Subtype plus Identifier fields, Subtype is 1 octet, and Identifier is variable length. The option has no alignment requirements.