A new IPv6 extension header, the mobility header, is designed to contain the MIPv6 signalling messages. The mobility header is used by Mobile Nodes, Home Agents and Correspondent Nodes for all messaging related binding creation and management. The format of the mobility header is illustrated in Figure 10-3.

The mobility header is identified by a next header value of 135 (decimal) in the IPv6 header (or an alternative preceding header if there is one). The ‘MH Type’ field identifies the specific mobility message in question and can be one of the following:

• Home Test Init (HoTI)
• Care-of Test Init (CoTI)
• Home Test (HoT)
• Care-of Test (CoT)
• Binding Request (BR)
• Binding Update (BU)
• Binding Acknowledgement (BA)
• Binding Missing (BM).

Due to the use of the new mobility header, the piggybacking of MIPv6 signalling with data is no longer possible. However, a separate extension to the protocol that will allow piggybacking in the presence of the mobility header may become available in the near future.