Mobile IPv6: the final spec

Keiichi Shima
IIJ Technology Laboratory


Mobile IPv6 is a technical specification to add mobile communication capability to IPv6. Its standardization has been handled by Mobile IPv6 Working Group (MIP6 WG) in the IETF. Many of you may be wondering what has come out of MIP6 standardization because it appears that nothing has happened since the working group submitted the last spec in February 2003. I will introduce you to the progress in Mobile IPv6 standardization work for the last one year.


Standardization status

The latest draft version of Mobile IPv6 is ID 24. ID 24 was approved by IESG on July 17, 2003 as an RFC. Normally, approved spec becomes an RFC in a short period of time, but Mobile IPv6 has not become an RFC as of May 25, partly due to time required by IANA to issue protocol number. Currently, the working group is circulating the last draft to correct wording. MIP6 WG is finally putting an end to the long standardization process that took eight years.


Mobile IPv6 overview

There are three elements in Mobile IPv6: “mobile node” that conducts communication while in move, “home agent” that temporarily responds to communication requests on behalf of mobile nodes, and “correspondent node” that communicates with mobile nodes. Every time a mobile node moves to a different network, tells its home agent its new address and its home address (its address on the home network). This message is called a Binding Update. The home agent conducts appropriate packet forwarding based on the address of the mobile node, so correspondent node can always communicate with the mobile node wherever it is, using home address (figure 1). In addition, a correspondent node supporting IPv6 can directly communicate with a mobile node, with the mobile node sending the correspondent node Binding Updates, after creation of authenticator value by token exchange taking advantage of Return Routability(figure 2).


Figure 1 Home agent forwards packets


Figure 2 Mobile node can move to direct communication


Highlights of last I-D revision

During the last one year, many vague expressions were clarified. Some corrections were also made, reflecting issues found through operation of actual implementation at interoperability tests. Below are some of the more important corrections among them.


Detection of routers with the same link-local address

Earlier specification said that a mobile node confirms that it moved between networks by checking reachability to network default router. Normally, router reachability check is conducted against the link-local address of the router. But the mobile node cannot recognize the change of network if routers on the two networks have the same link-local address. Different routers can have the same link-local address frequently when VLAN is used for multiplexing one physical interface. In Mobile IPv6, router advertisement is enhanced so that router includes its own global address in the prefix information in its router advertisement. New spec recommends the mobile node to check router reachability against the router global addresses. But router needs to implement Mobile IPv6 enhancements to utilize this revised mechanism.

For a more fundamental solution, administrator should be careful not to assign the same link-local address to different routers.


Calculation of authenticator value in De-registration

In Return Routability, authenticator value is calculated using a) token exchanged between the mobile node and the correspondent node, b) care-of address of the mobile node, and c) home address of the mobile node. Authenticator value is used by a mobile node to prove the authenticity of the home address-care-of-address binding it tells to correspondent node. Among the information used for calculation of authenticator value, c) is used only in the binding registration, not in de-registration. De-registration occurs when a mobile node returns its home network. In this case, home address and care-of address are the same, so home address is not necessary for this calculation. But when a mobile node makes a de-registration from foreign network, care-of address is different from home address. Authenticator value in de-registration is to confirm authenticity of the source address of a node making de-registration. Earlier specification used care-of address for this but a mobile node clearly should use its home address when making de-registration on foreign network. This has been corrected in the latest document.


Future of standardization work

Several interoperability testing have been conducted successfully after Mobile IPv6 specification reached the current version. Technological issues have been solved. We are in the stage to add sophistication to the specification based on real world needs from through actual deployments.