Mix together the cake mix and eggs. Fold in the sour cream.
Mix in the vanilla, 1 cup sugar, oil and pecans.
Pour half of batter into a 9 x 13 inch pan.
Combine the ground cinammon and brown sugar.
Sprinkle over the batter.
Pour the other half of the batter over top.
Bake at 350 degrees F (175 degrees C) for 50 minutes.
To make Icing: Bring to a boil 1/2 cup butter or margarine, 1 cup sugar, buttermilk and baking soda. Prick cake all over with fork and pour hot icing on cake.