title: Old class library on new .NET projects
body: <p>Sorry I am old school programmer, where all projects of a solution used to target the same .NET Framework version. However I see developers creating .NET 4.6.1 projects referencing .NET 4.5.1 class libraries.</p>
  <blockquote>
  <p>Is it ok to reference older version of class library inside newer MVC / Web
  Api project?</p>
  </blockquote>
  <p>For green field projects, by mixing different run times are we not headed in similar situation like DLL hell, not to mention performance penalty, if any, caused by simultaneous loading of run times in production server.</p>