We proposed a nanoplasmonic optical filtering technique based on complementary split-ring resonator structures. Interestingly, the proper plasmonic modes of the nanoring in the side-coupled arrangement can be selected and excited by the proposed structures. It is observed that the non-integer modes can be excited due to the presence of a metallic nano-wall as well as the integer modes. Furthermore, the numerical results indicate that the optical transmission spectrum of the investigated filter can be efficiently modified and tuned by manipulation either the position or the width of the employed nano-wall inside the metal-insulator-metal ring. The antinodes of the magnetic field of these modes, located on the symmetry plane of the proposed structures, can be manipulated by the position of the wall. Additionally, these modes, in particular the fundamental mode, are highly sensitive to the nano-wall dimensions. It indicates that the proposed nanofilter is a promising candidate as a tunable filter in nanophotonics applications.