Windows XP Service Pack 2 (SP2) , there is no version officially named ".NET Framework 3.1". Instead, you likely need .NET Framework 3.5 Service Pack 1 (SP1) , which is the last version fully supported on XP SP2. Microsoft Learn Critical Prerequisites Before installing .NET 3.5 SP1, ensure your system has Windows Installer 3.1

. The .NET 3.5 installer will fail if this component is missing. Microsoft Learn Offline Installer Download To install without an internet connection, you must use the Full Redistributable Package (approx. 231 MB) rather than the standard web bootstrapper. Official Link: Microsoft .NET Framework 3.5 SP1 (Full Package) Alternative Support: For direct archive links, technical communities like maintain historical offline installer lists. Installation Steps Microsoft .NET Framework 3.5 Service pack 1 (Full Package)

Unfortunately, .NET Framework 3.1 does not exist. This is a common confusion between two different Microsoft technologies:

.NET Core 3.1 was released in 2019 and does not support Windows XP — its minimum supported OS is Windows 7 / Windows Server 2012 R2.

Error 3: "File Hash mismatch" or "Cabinet file corrupt"

Fix: Your downloaded dotnetfx35.exe is truncated or corrupted. Redownload it. Compare the file size: Exactly 231,256,432 bytes (varies slightly by language, but roughly 231 MB). If you have 50 MB, you have the web installer.

1. .NET Framework 3.5 SP1 (full offline installer)

On Windows XP, this offline installer works without an internet connection, but you may need to extract it first:
dotnetfx35.exe /x (to extract to a folder), then run setup.exe.

What you likely need for Windows XP SP2

If you are running software that asks for a “.NET Framework 3.1” dependency, it probably means .NET Framework 3.5 (which includes 2.0 and 3.0). Alternatively, the software might need .NET Framework 4.0 (up to 4.0.3).

Warning – Avoid Fake “.NET 3.1” Downloads

Many third-party sites (like downloadmicrosoft.net, allexe-downloads.com) offer “NET Framework 3.1 offline installer.exe” (~2–5 MB). These are dangerous because: