Internet access is not required to install SQL Server. However, you do need to work out what components will also be installed when you do your SQL Server install and where their install media is.
One of the biggest problems is .Net 3, especially with Windows 2012 / 2012 R2. .Net3 cannot just be enabled on W2012, it has to be installed using platform-specific install media.
This link http://sqlserverfinebuild.codeplex.com/wikipage?title=Install%20.Net%203.5
says when the .Net3 install media is ready to run and where it must be downloaded. For W2012 R2 and Windows 8.1, you need to get the install media from the \sxs folder for those operating systems as they use different files to W2012 and Windows 8.
Take a look at http://sqlserverfinebuild.codeplex.com/wikipage?title=SQL%20Media%20Preparation
and click on the SQL version you want to install. Then scroll down to find the mandatory software you must have to complete the install.
Original author: SQL Server FineBuild 1-click install and best practice configuration of SQL Server 2017 2016, 2014, 2012, 2008 R2, 2008 and 2005. 1 Dec 2016
: now over 39,000 downloads.
Disclaimer: All information provided is a personal opinion that may not match reality.
Quote: "When I give food to the poor they call me a saint. When I ask why they are poor they call me a communist." - Archbishop Hélder Câmara