What is the maximum cooldown reduction someone can have in game?

It is possible to have up to 9% from masteries and around 15% from runes in addition to cooldown reduction from items in game. Is this additional 21% included in the maximum capacity from items?

Hypothetically, if the maximum cooldown reduction is 25%, and I have 21% from runes and masteries, would the maximum bonus from an item like nashor's tooth be 4% or would I get the full 25% percent, plus my 21%?

Thank you