code: func (d *DUIDLLT) MarshalBinary() ([]byte, error) {
  	// 2 bytes: DUID type
  	// 2 bytes: hardware type
  	// 4 bytes: time duration
  	// N bytes: hardware address
  	b := buffer.New(nil)
  
  	b.Write16(uint16(d.Type))
  	b.Write16(d.HardwareType)
  	b.Write32(uint32(d.Time / time.Second))
  	b.WriteBytes(d.HardwareAddr)
  
  	return b.Data(), nil
  }
docs: // MarshalBinary allocates a byte slice containing the data from a DUIDLLT.