The Mobility Header Type field identifies the type of Mobility message. Table B-29 is an overview of the Mobility messages.
Table B-29. Mobility message types
Binding Refresh Request
Sent by CN requesting the MN to update its binding.
Home Test Init
Sent by the MN to initiate the Return Routability Procedure and request a Home Keygen token from a CN. Sent to the CN through the tunnel via HA.
Care-of Test Init
Sent by the MN to initiate the Return Routability Procedure and request a Keygen token from a CN. Sent to the CN directly.
Home Test Message
Response to a Home Test Init message (type 1). Sent from the CN to MN. Contains a cookie and a Home Keygen token for the authorization in the Return Routability Process. Sent through the tunnel via HA.
Care-of Test Message
Response to Care-of Test Init message (type 2). Sent from CN to MN. Contains cookie and a Care-of Keygen token for the authorization in the Return Routability Procedure. Sent to the MN directly.
Sent by MN to notify a change of its care-of address. This message is explained in more detail later in the chapter.
Sent as acknowledgement for receipt of a Binding Update message. This message is explained in more detail later in the chapter.
Sent by CN to signal an error related to mobility, such as an inappropriate attempt to use the Home Address destination option without an existing binding. The status field can have the following values:
1 = unkown binding for Home Address Destination option
2 = unrecognized MH type value
Fast Binding Update
Identical to binding update message, only with slightly different processing rules.
Fast Binding Ack
Sent as acknowledgement for receipt of a Fast Binding Update message.
Fast Neighbor Advertisement
Sent by mobile node to announce itself to its new access router.
Values 8, 9, and 10 have been assigned in RFC 4068 "Fast Handovers for Mobile IPv6." Find all message and option types as well as status codes at http://www.iana.org/assignments/mobility-parameters.
Table B-30 shows the status values of the Binding Update. Values in the range of 0 to 127 indicate that the Binding Update has been accepted. Values above 128 indicate that the Binding Update has not been accepted.
Table B-30. Status values in the Binding Acknowledgement
Binding Update accepted
Accepted but prefix discovery necessary
Home Registration not supported
Not home subnet
Not home agent for this mobile node
Duplicate Address Detection failed
Sequence number out of window
Expired home nonce index
Expired care-of nonce index
Registration type change disallowed
Mobile Router Operation not permitted
Not Authorized for Prefix
Forwarding Setup failed
Table B-31 shows an overview of the currently defined options for mobility messages.
Table B-31. Mobility options
Used to insert one padding Byte. This option has a special format; it contains only a type field, and no fields for length and data.
Used to insert two or more padding Bytes.
Binding Refresh Advice
Indicates the remaining time until the MN should send a new home registration to HA. Only valid in Binding Acks sent from the HA in response to a home registration. The interval must be shorter than the lifetime value in the Binding Acknowledgement. A time unit is four seconds.
Alternate Care-of address
Contains an address to use as the care-of address for the binding rather than using the Source address of the packet as the care-of address. Only in Binding Update messages.
Has two additional fields besides the Type and Length field. The Home Nonce Index field tells the CN which nonce value to use when producing the Home Keygen Token. The Care-of Nonce field indicates the value for generating the Care-of Keygen Token. Valid only in the Binding Update message sent to a CN, and only when present together with a Binding Authorization Data option.
Binding Authorization Data
Contains a cryptographic value that can be used to determine that the message in question comes from the right authority. Rules for calculating this value depend on the authorization procedure used. Must always be the last option in the MH. Only valid in Binding Update and Binding Acknowledgement. Used for the Return Routability process. In this case, the calculation of the Authenticator value is based on care-of address of MN, IPv6 address of CN, and data from the MH.
Mobile Network Prefix Option
Included in the Binding Update to indicate the prefix information for the Mobile Network to the HA.
Mobility Header Link-Layer Address option
Link-layer address option carried in an MH; used for Fast Handovers.
Optional suboption in the MH to specify the type of identifier used to identify the MN.
When receiving a binding update, the HA must check the timestamp field. If it is invalid, it replies with a binding acknowledgment including this status code.
Defines the type of mobility option.
Contains the home address of MN. Sent by MN when away from home to indicate its home address to the receiver. Carried in a Destination Options header. Must be inserted after Routing header and before Fragment, AH, or ESP header (if present).