Mobile IPv4 Extension for Carrying Network Access Identifiers
Extracted elements (20)
The extension was created because AAA infrastructures such as Diameter use realm-based routing and need the FQDN identity of the home agent, not just its IP address. A reverse DNS lookup on the HA IP address may not reliably yield the HA's FQDN identity, so the HA must include its own identity explicitly in registration replies.
The NAI Carrying Extension uses type 136 (skippable) so that nodes not understanding the extension can safely ignore it. The content and format are intentionally not specific to AAA NAIs, allowing future NAI types to reuse the same sub-type numbering space.
The NAI Carrying Extension should be assigned type values from both the IANA number space for Mobile IPv4 skippable extensions and from the IANA number space for Mobile IPv4 advertisement extensions, with ideally the same value assigned from both spaces.
A foreign agent that receives the Home Agent NAI in a registration request SHOULD include the Home Agent NAI when requesting Mobile Node authentication through the AAA infrastructure if the AAA protocol used can carry the information.
A Home Agent using the HA Identity extension MUST provide it in the first Registration Reply sent to a Mobile Node which is not currently registered. The extension only needs to be included in subsequent Registration Replies if the same extension is included in Registration Requests from the same MN.
A mobile node SHOULD save the latest AAAH Identity received in a registration reply message and SHOULD provide the AAAH Identity in every registration request sent when re-authenticating, for efficiency reasons.
A mobile node that receives the HA Identity extension in a Registration Reply MUST provide it in every subsequent registration request when re-authentication is needed.
If an HA appended a NAI Carrying Extension to a Registration Reply but does not receive the NAI extension in subsequent Registration Requests from the MN, the HA SHOULD NOT append this NAI extension to further Registration Reply messages to that MN, as it can assume the MN does not understand the extension.
If several AAA servers exist in the Home Network, a Home Agent providing AAAH selection support MUST provide the AAAH identity in the first Registration Reply sent to the Mobile Node.
If the mobile node requires a specific home agent and has the NAI available, it MUST provide the HA Identity extension in its initial registration request.
Mobile IP messages that carry the NAI Carrying Extension MUST be authenticated as described in RFC 2794, unless other authentication methods have been agreed upon.
The Length field of the NAI Carrying Extension MUST be set to 1 plus the total length of the NAI field.
When a foreign agent adds a NAI Carrying Extension to a registration message, the extension MUST appear prior to any authentication extensions added by the FA.
When a mobile node or home agent adds a NAI Carrying Extension to a registration message, the extension MUST appear prior to any authentication extensions.
The AAAH Identity subtype uses sub-type 2 of the NAI Carrying Extension and contains the NAI of the home AAA server in the form hostname@realm, where hostname and realm together form the complete FQDN (hostname.realm) of the home AAA server.
The HA Identity subtype uses sub-type 1 of the NAI Carrying Extension and contains the NAI of the Home Agent in the form hostname@realm, where hostname and realm together form the complete FQDN (hostname.realm) of the HA.
The NAI Carrying Extension (type 136, skippable) may be used in Mobile IP Registration Request and Reply messages, and in Mobile IP Agent Advertisements. It carries identity information in the form of a Network Access Identifier (NAI) and uses a sub-type field to distinguish the specific kind of NAI being carried.
IANA assigned type number 136 to the Mobile IP NAI Carrying Extension (as a skippable extension). A new sub-type numbering space was created for this extension; sub-types 1 (HA Identity) and 2 (AAAH Identity) are assigned in this document. New sub-type approvals require Expert Review and a specification.
The identities sent in the NAI Carrying Extension MAY be sent in the clear over the network. The authors do not envision this creating security issues, and the specification does not lessen the security of Mobile IP messages since they must be authenticated per RFC 2794.
The NAI Carrying Extension has four fields: Type (1 octet, value 136), Length (1 octet, unsigned integer excluding Type and Length fields, set to 1 plus the total length of the NAI field), Sub-Type (1 octet describing the specific NAI type), and NAI (variable-length string).