DNS Update Exchange (GSS-TSIG hook)

     ,-------------.                ,----------.
     |Kea D2 server|                |DNS server|
     `------+------'                `----+-----'
            |DNS update request (signed) |
            |---------------------------->
            |                            |
            |DNS update response (signed)|
            |<----------------------------
     ,------+------.                ,----+-----.
     |Kea D2 server|                |DNS server|
     `-------------'                `----------'