Diameter Mobile IPv6: Support for Network Access Server to Diameter Server Interaction
Extracted elements (23)
Dynamic assignment of MIPv6 home registration information via AAA is preferred over static provisioning because static approaches do not address load balancing, failover, opportunistic home link assignment, local HA proximity, or adaptation to topological changes.
It is RECOMMENDED that MIP-Home-Agent-Host is always included in MIP6-Agent-Info so that the HA can be associated with the realm of the Diameter entity that added the AVP via the Destination-Realm sub-AVP, aiding realm-based routing.
MIP-Home-Agent-Address takes precedence over MIP-Home-Agent-Host when both appear in MIP6-Agent-Info because MIP-Home-Agent-Address points to a specific home agent, while MIP-Home-Agent-Host may identify a group of HAs within the same realm.
The MIP6-Agent-Info ABNF allows up to two MIPv6 HA addresses to support deployments where the HA has both IPv6 and IPv4 addresses, particularly addressing Dual Stack Mobile IPv6 (DSMIPv6) deployment scenarios.
This document does not define a new Diameter application; instead the new AVPs can be used with any present and future Diameter applications where permitted by the command ABNF. This avoids requiring new application negotiation for MIPv6 bootstrapping.
The MIP6-Feature-Vector AVP (code 124) and MIP6-Home-Link-Prefix AVP (code 125) are allocated from the RADIUS Attribute Type space (values 0-255) to maintain RADIUS backward compatibility, while MIP6-Agent-Info (code 486) is allocated from the normal Diameter AVP Code space.
The NAS-to-HAAA interface described in this document is not tied to DHCPv6 as the only mechanism to convey MIPv6-related configuration parameters from the NAS/Diameter client to the mobile node; other mechanisms are permitted.
This specification covers bootstrapping of MIPv6 HA information and home link prefix assignment, but explicitly does not address creation of the Security Association between the MN and HA for MIPv6 purposes; SA creation is out of scope.
If both the MIP-Home-Agent-Address and MIP-Home-Agent-Host AVPs are present in the MIP6-Agent-Info, the MIP-Home-Agent-Address SHOULD have precedence over the MIP-Home-Agent-Host because it points to a specific home agent whereas MIP-Home-Agent-Host may identify a group.
Sending and receiving the MIP6-Feature-Vector AVP with value 0 MUST be supported, although it does not convey specific bootstrapping guidance.
The MIP6-Home-Link-Prefix AVP MUST encode the home network prefix as the 8-bit prefix length (one octet) followed by the 128-bit prefix field (16 octets), with trailing bits after the prefix length set to zero.
When the MIP6-Agent-Info AVP is present in a message, it MUST contain either the MIP-Home-Agent-Address AVP, the MIP-Home-Agent-Host AVP, or both AVPs.
The LOCAL_HOME_AGENT_ASSIGNMENT flag (0x0000000000000002) in the MIP6-Feature-Vector AVP signals that a local home agent outside the home realm is requested (in request) or authorized (in answer). The local HA may be assigned by the NAS, LAAA, or VAAA depending on deployment.
The MIP-Home-Agent-Address AVP (AVP Code 334, from RFC 4004) is of type Address and contains the IPv6 or IPv4 address of the MIPv6 home agent. It may carry both IPv6 and IPv4 addresses to support Dual Stack Mobile IPv6 deployments.
The MIP-Home-Agent-Host AVP (AVP Code 348, from RFC 4004) is of type Grouped and contains the identity of the assigned MIPv6 home agent via Destination-Realm and Destination-Host sub-AVPs, offering DNS-based indirection. It is RECOMMENDED that the Destination-Host AVP identifies exactly one HA.
The MIP6-Agent-Info AVP (AVP code 486) is of type Grouped and contains necessary information to assign a home agent to the mobile node. It MUST contain either the MIP-Home-Agent-Address AVP, the MIP-Home-Agent-Host AVP, or both. It may also include an optional MIP6-Home-Link-Prefix sub-AVP.
The MIP6-Feature-Vector AVP (AVP Code 124) is of type Unsigned64 and carries a 64-bit flags field indicating supported capabilities of the NAS/ASP. It is used bidirectionally: the NAS advertises capabilities to the Diameter server, and the server echoes back which are authorized.
The MIP6_INTEGRATED flag (0x0000000000000001) in the MIP6-Feature-Vector AVP indicates support for the Mobile IPv6 integrated scenario bootstrapping. When set by the NAS it signals NAS capability; when set by the Diameter server it confirms authorization.
IANA created a new 'Mobility Capability' registry for MIP6-Feature-Vector flags. Initial values are MIP6_INTEGRATED (0x0000000000000001) and LOCAL_HOME_AGENT_ASSIGNMENT (0x0000000000000002). New values must be powers of two (2^x, x >= 2) and require Specification Required policy.
Three new AVPs are registered: MIP6-Agent-Info (AVP code 486) in the Diameter AVP Code space, and MIP6-Feature-Vector (124) and MIP6-Home-Link-Prefix (125) in the RADIUS-compatible space.
Security associations protecting Diameter messages that enable global positioning and allocation of home agents must be carefully configured. Diameter messages may traverse AAA brokers or proxies, so NAS-to-server security relies on the security properties of all intermediate Diameter agents.
The security considerations from the Diameter base protocol (RFC 3588), Diameter NASREQ (RFC 4005), and Diameter EAP application (RFC 4072) are applicable. Developers should pay special attention to securing messages conveying HA assignment and bootstrapping parameters.
The MIP6-Home-Link-Prefix AVP (AVP Code 125) is of type OctetString encoding the home network prefix as one octet of prefix length followed by 16 octets (128 bits) for the prefix value in network byte order. Trailing bits after the prefix length MUST be set to zero.