def METHOD_NAME(self) -> int:
    """Get length of KNX/IP body."""
    data_size = len(self.data) + (len(self.data) % 2) if self._has_data() else 0
    return (
        _TunnellingFeature.HEADER_LENGTH
        + _TunnellingFeature.FEATURE_ID_LENGTH
        + data_size
    )