Mobile IP Network Access Identifier Extension for IPv4
updates
- rfc-2290 — Mobile-IPv4 Configuration Option for PPP IPCP
Extracted elements (16)
Because the NAI uniquely identifies the mobile node, a home address is not always necessary for authentication and authorization with a foreign AAA server. Allowing a zero Home Address in the Registration Request enables dynamic home address assignment via AAA infrastructure in foreign domains.
The Home Domain Allocation Function (HDAF) is introduced as an intermediary that receives Registration Requests from foreign agents, extracts the NAI domain, and forwards requests to an appropriate Home Agent. This decouples home address allocation from static home agent configuration.
RFC 2794 updates RFC 2290 (Mobile-IPv4 Configuration Option for IPCP): the Mobile Node's Home Address field in the IPCP option, which RFC 2290 required to be nonzero, is now allowed to be zero when the mobile node uses the NAI extension to obtain a home address after PPP establishment.
Supporting NAI-based registrations for Mobile IPv6 is explicitly out of scope for RFC 2794. The document notes that IPv6 lacks deployed mechanisms equivalent to the foreign agent model, and sketches how Stateless Address Autoconfiguration or DHCPv6 might be extended in the future.
If Home Address is zero in the Registration Request, the foreign agent MUST use the NAI instead in its pending registration request records, along with the Identification field as usual.
If the foreign agent cannot manage pending registration records using the NAI (when Home Address is zero), it MUST return a Registration Reply with Code NONZERO_HOMEADDR_REQD (96).
If the mobile node includes the Mobile Node NAI extension in its Registration Request, the Registration Reply from the home agent MUST include the Mobile Node NAI extension. If not, the foreign agent SHOULD send the Reply to the mobile node with Code changed to MISSING_NAI (97).
The Mobile Node NAI extension MUST appear in the Registration Request before both the Mobile-Home Authentication extension and Mobile-Foreign Authentication extension, if present.
The Registration Reply MUST include a nonzero Home Agent address and mobile node's Home Address. If not, the foreign agent SHOULD send the Reply with Code MISSING_HOME_AGENT (98) or MISSING_HOMEADDR (99) respectively.
When the Mobile Node NAI extension is present in the Registration Request, the Home Address field MAY be set to zero (0) to request that a home address be assigned.
Four error codes are defined for Registration Reply: NONZERO_HOMEADDR_REQD (96), MISSING_NAI (97), MISSING_HOME_AGENT (98), and MISSING_HOMEADDR (99). All fall in the foreign-agent rejection range (64–127).
The Mobile Node NAI Extension carries the user's Network Access Identifier in a Mobile IP Registration Request, using Type 131 (skippable). It contains a one-byte Type, one-byte Length, and a variable-length MN-NAI string formatted per RFC 2486.
When the IPCP IP Address Configuration Option has IP address zero, the PPP peer allocates and assigns a co-located care-of address to the mobile node. If the option carries a nonzero address, that address is assigned as the co-located care-of address.
IANA assigns Type value 131 to the Mobile Node NAI extension as a skippable Mobile IP registration extension, and records the four error Code values (96–99) defined in Section 5 as foreign-agent rejection codes.
Mobile IP registration messages are authenticated and the authentication is verified by the recipient. The specification does not prohibit sending the NAI in the clear over the network, but this is not considered a security issue since NAIs are not secret credentials.
The Mobile Node NAI extension encoding: Type (1 byte, value 131), Length (1 byte, length of MN-NAI field in bytes), MN-NAI (variable, NAI format string per RFC 2486).