DHCP Options for Home Information Discovery in Mobile IPv6 (MIPv6)
Extracted elements (28)
Despite completing a home information discovery procedure, a mobile node may continue using its old home agent to avoid losing current sessions. Discovery and switching are decoupled to support seamless mobility.
IPv4 transport to a home agent is supported by encoding the IPv4 address as an IPv4-Embedded IPv6 address using the Well-Known Prefix (RFC 6052), rather than defining separate IPv4-specific options. This keeps the option set consistent while enabling dual-stack operation per RFC 5555.
Three distinct Home Network Information option types (Visited, Identified, Unrestricted) are defined to cover the three principal discovery scenarios: local home agent discovery, home-domain-specific discovery, and operator-administered discovery. This separation lets clients signal precisely what kind of home agent they seek.
Mobile nodes MAY obtain MIPv6 configuration information during either a stateful DHCPv6 exchange (RFC 3315) or a stateless exchange (RFC 3736); both modes are supported with the same option set.
The NAS (Network Access Server) is assumed to be co-located with a DHCP relay agent or DHCP server for the bootstrapping scenario described in RFC 5447. If the NAS is not co-located, the server may be unable to provide home network information obtained from the NAS.
A client that requests any of the three Home Network Information options in the ORO MUST also request the Home Network ID FQDN option, the Home Network Prefix option, the Home Agent Address option, and the Home Agent FQDN option.
A client that sends more than one Home Network ID FQDN option MUST also request the Home Network ID option in the ORO, to allow the server to correlate responses.
A DHCP server that maintains a Home Network ID FQDN table SHOULD include an Identified Home Network Information option for each matching FQDN found in the client's request.
A mobile node requesting the Identified Home Network Information option MUST include a Client Home Network ID FQDN option identifying the MSP. The target MSP may be the mobile node's home MSP or any MSP with a trusted roaming relationship.
Each Identified Home Network Information option sent by a relay agent must contain a Home Network ID FQDN option identical to the one sent by the client, so the client can identify which network each response pertains to.
If a Home Network Information option does not contain complete configuration information, the client MUST silently discard that option. Options received outside any Home Network Information container (unencapsulated) MUST also be silently discarded.
If a misconfigured server returns an Identified Home Network Information option that does not contain a Home Network ID FQDN corresponding to one the client requested, the client MUST silently discard that option.
If the DHCP server responds to a MIPv6-related stateless configuration request with an Information Request Timer option, the mobile node SHOULD attempt to reconfigure when the IRT expires.
If the mobile node has no preference for a particular home network, it SHOULD request the Unrestricted Home Network Information option and SHOULD NOT request the Visited or Identified variants.
Mobile nodes obtaining MIPv6 configuration via stateful DHCPv6 SHOULD include the same options in every message sent to the server. For stateless exchanges, mobile nodes SHOULD reconfigure whenever a change in the attached network is detected.
Relay agents that supply home network information MUST encapsulate those options in a Relay-Supplied Options option per RFC 6422. Identified Home Network Information options included by relay agents MUST correspond to Home Network ID FQDNs in the client request.
OPTION_MIP6_HNIDF (code 49) is a new DHCPv6 option used by mobile nodes to communicate an FQDN identifying the target home network for which configuration is requested. When a server responds with an Identified Home Network Information option, this option MUST be encapsulated within it to identify the home network.
OPTION_MIP6_IDINF (code 69), the Identified Home Network Information option, is used by relay agents and DHCP servers to provide information about a home network identified by a specific Home Network ID FQDN option sent by the mobile node.
OPTION_MIP6_UDINF (code 70), the Unrestricted Home Network Information option, is used by relay agents and DHCP servers to provide home network information as configured by the DHCP administrator, with no specific target network constraint.
OPTION_MIP6_VDINF (code 50), the Visited Home Network Information option, is used by relay agents and DHCP servers to provide information about the local (visited) home network. It acts as a container carrying sub-options for the local ASP.
IANA assigned seven new DHCPv6 Option Codes: 49 (OPTION_MIP6_HNIDF), 50 (OPTION_MIP6_VDINF), 69 (OPTION_MIP6_IDINF), 70 (OPTION_MIP6_UDINF), 71 (OPTION_MIP6_HNP), 72 (OPTION_MIP6_HAA), 73 (OPTION_MIP6_HAF) in the DHCPv6 parameters registry.
Attackers cannot trick mobile nodes into using incorrect home agents in a meaningful way because MIPv6 communication between mobile nodes and home agents employs mutual authentication; the authentic source of home agent information is MIPv6 signaling, not DHCP.
Secure delivery of home agent and home network information relies entirely on DHCP security mechanisms; the new options introduce no additional DHCP security impact. Operators must also ensure secure delivery of mobile IP information to the DHCP server through out-of-band mechanisms.
These mechanisms may allow attackers to enumerate home agent addresses, which is valuable in IPv6 where brute-force address scanning is impractical. Leaked topology and prefix information could assist targeted attacks, and DHCP manipulation could cause denial of service by redirecting mobile nodes to suboptimal or unreachable home agents.
OPTION_MIP6_HAA (code 72) carries a 16-byte IPv6 Address field for the home agent. For IPv4-only infrastructures, the address is encoded as an IPv4-Embedded IPv6 address using the Well-Known Prefix per RFC 6052.
OPTION_MIP6_HAF (code 73) carries a variable-length FQDN field encoded per RFC 3315 Section 8, resolving to one or more A or AAAA records for the home agent. It must appear only inside one of the three Home Network Information container options.
OPTION_MIP6_HNIDF (code 49) carries a variable-length Home Network Identifier FQDN field encoded per RFC 3315 Section 8 (DNS wire format). The option header is the standard 2-byte option-code plus 2-byte option-len.
OPTION_MIP6_HNP (code 71) carries a 1-byte Prefix-len field followed by the variable-length IPv6 home network Prefix. It must appear only inside one of the three Home Network Information container options.