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6.5. Destination Advertisement Object Acknowledgement (DAO-ACK)

The DAO-ACK message is sent as a unicast packet by a DAO recipient (a DAO parent or DODAG root) in response to a unicast DAO message.

6.5.1. Format of the DAO-ACK Base Object​

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID |D|  Reserved   |  DAOSequence  |    Status     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
+                                                               +
|                                                               |
+                            DODAGID*                           +
|                                                               |
+                                                               +
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Option(s)...
+-+-+-+-+-+-+-+-+

The '*' denotes that the DODAGID is not always present, as described below.

Figure 17: The DAO ACK Base Object

  • RPLInstanceID: 8-bit field indicating the topology instance associated with the DODAG, as learned from the DIO.

  • D: The 'D' flag indicates that the DODAGID field is present. This would typically only be set when a local RPLInstanceID is used.

  • Reserved: The 7-bit field, reserved for flags.

  • DAOSequence: Incremented at each DAO message from a node, and echoed in the DAO-ACK by the recipient. The DAOSequence is used to correlate a DAO message and a DAO ACK message and is not to be confused with the Transit Information option Path Sequence that is associated to a given Target Down the DODAG.

  • Status: Indicates the completion. Status 0 is defined as unqualified acceptance in this specification. The remaining status values are reserved as rejection codes. No rejection status codes are defined in this specification, although status codes SHOULD be allocated according to the following guidelines in future specifications:

    • 0: Unqualified acceptance (i.e., the node receiving the DAO-ACK is not rejected).
    • 1-127: Not an outright rejection; the node sending the DAO-ACK is willing to act as a parent, but the receiving node is suggested to find and use an alternate parent instead.
    • 127-255: Rejection; the node sending the DAO-ACK is unwilling to act as a parent.

  • DODAGID (optional): 128-bit unsigned integer set by a DODAG root that uniquely identifies a DODAG. This field is only present when the 'D' flag is set. Typically, this field is only present when a local RPLInstanceID is in use in order to identify the DODAGID that is associated with the RPLInstanceID. When a global RPLInstanceID is in use, this field need not be present.

  • Unassigned bits of the DAO-ACK Base are reserved. They MUST be set to zero on transmission and MUST be ignored on reception.

6.5.2. Secure DAO-ACK​

A Secure DAO-ACK message follows the format in Figure 7, where the base format is the DAO-ACK message shown in Figure 17.

6.5.3. DAO-ACK Options​

This specification does not define any options to be carried by the DAO-ACK message.

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