>Does IIS support the migration of a setup from Windows Server 2003 to 2012? As there are a lot of Web sites on a specific server, we would like to avoid having to reconfigure all that.

2003 -> 2012? No way. Heck you can barely upgrade from 2012 -> 2016.

2003 used a completely different metabase setup than later versions so no way that will migrate unless there's some custom tool that does it explicitly using the Admin APIs. Nothing that is built in for sure though.

Frankly - you'd probably want to make sure you do this manually since so much has changed between these versions.

+++ Rick ---