tension The mobility extension, described in Figure 9.2, is attached to the IPv6 header and allows the exchange of information between the mobile node, on the one hand, and the correspondent node or the home agent, on the other. Payload Proto Header Length MH Type Reserved Checksum Message Data Figure 9.2. Mobility extension format S2c Tunnel Establishment This information relates to the registration of the mobile node with the correspondent node or the host agent, for the association of addresses HoA and CoA. The Next Header field in the header preceding the mobility extension has a value of 135. Proto Payload: this field, coded on one byte, has a value of 59, indicating termination of extensions chaining. Header Length: this field, coded on one byte, defines the size of the extension. MH (Mobility Header) Type: this field, coded on one byte, defines the type of mobility extension: - 0) Binding Refresh Request. This extension is transmitted by the correspondent node or by the home agent to the mobile node in order to update the link between the HoA and CoA. - 1) Home Test Init (HoTI). This extension initializes the Return Routability procedure on the indirect path between the mobile node and the correspondent node. - 2) Care-of Test Init (CoTI). This extension initializes the Return Routability procedure on the direct path between the mobile node and the correspondent node. - 3) Home Test (HoT). This extension is the answer to the HoTI extension. It contains the cryptographic information (Home Keygen Token). -4) Care-of Test (CoT). This extension is the answer to the HoTI extension. It contains the cryptographic information (Care-of Keygen Token). - 5) Binding Update. This extension is transmitted by the mobile node to link the HoA contained in the Home Address option of the Destination extension to the CoA contained in the source address of the IPv6 header or in the Alternate Care-of Address option. - 6) Binding Acknowledgment. This extension is passed by the correspondent node or by the home agent to acknowled