What are the most effective and common methodologies or practices of Network security used most companies?

i think SANS is a very good reference on many accords

but it is never wise to adhere to one school of thought throughout your entire network

i myself am always looking for what cons a specific approach or method has rather than just looking at the pros and trusting the method and approach just because it comes from a reputable source

besides, i have found that most of the time i improvise and tailor my own method to solve a problem

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