Round Tripping is a revese engineering technique that allow us to decompile an assembly from a certain application. Ildasm.exe can be used for this purpose, and ILAsm is used to recompiled the assembly . The MSIL Disassembler( Ildasm.exe) is a companion tool to the MSIL Assembler (Ilasm.exe). Ildasm.exe takes a portable executable (PE) file that contains Microsoft intermediate language (MSIL) code and creates a text file suitable as input to Ilasm.exe. This tool is automatically installed with Visual Studio and with the Windows SDK.
The importance of Obfuscation
As mentioned before , Round Tripping is indeed a technique used to reverse engineer assemblies. Therefore, if you want to avoid your assemblies being reversed engineered or even worse, that the code is victim of malicious manipulation using the Ildasm and Ilasm tools, then its is advisable to apply it. There are different kinds of products that can be used for this purpose such as DeepSea, Crypto or Dotfuscator.