  In the present paper we study the structure of cyclic DNA codes of even
lenght over the ring $\mathbb{F}_2+u\mathbb{F}_2+u^2\mathbb{F}_2$ where
$u^3=0$. We investigate two presentations of cyclic codes of even lenght over
$\mathbb{F}_2+u\mathbb{F}_2+u^2\mathbb{F}_2$ satisfying the reverse constraint
and reverse-complement constraint.
