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
  +---------------+---------------+-------+-------+---------------+
  |     Kind      |     Length    |Subtype|(rsv)|E|  Address ID   |
  +---------------+---------------+-------+-------+---------------+
  |           Address (IPv4: 4 octets / IPv6: 16 octets)          |
  +-------------------------------+-------------------------------+
  |   Port (2 octets, optional)   |                               |
  +-------------------------------+                               |
  |                Truncated HMAC (8 octets, if E=0)              |
  |                               +-------------------------------+
  |                               |
  +-------------------------------+