Q: How to get numeric values for infinite sums?

Dear List,

please forgive my ignorance, as I am quite new to maxima. 
In case I oversaw any matching FAQ or manual, please give me an URL:

How can I make maxima to give me a numeric (or algebraic) result for 

  ratsimp(sum(1/k^2,k,1,inf));

? As the sum equals Zeta(2), I would like to get both:

(%i15) zeta(2);
(%o15) 1.644934066848226

and

(%i16)numer:false
(%o16) false
(%i17) zeta(2);
(%o17) %pi^2/6

Of course, I could try to replace "inf" with a high number, but I'd 
rather give an epsilon to limit depth by accuracy.

Thanks for your hints.
Ralf