Creating a valid software configuration of a product line can require laborious customizations involving multiple configuration file types, such as feature models, domain-specific languages, or preprocessor defines in C header files. Using configurable off-the-shelf components causes additional complexity. Without checking of constraints across file types boundaries already at configuration time, intricate inconsistencies are likely to be introduced--resulting in product defects, which are costly to discover and resolve later on. Up to now, at best ad-hoc solutions have been applied. To tackle this problem in a general way, we have developed an approach and a corresponding plug-in infrastructure. It allows for convenient definition and checking of constraints across configuration file types and product line boundaries. Internally, all configuration files are converted to models, facilitating the use of model-based constraint languages (e.g., OCL). Converter plug-ins for arbitrary confi...