  The work of Greither and Pareigis details the enumeration of the Hopf-Galois
structures (if any) on a given separable field extension. For an extension
$L/K$ which is classically Galois with $G=Gal(L/K)$ the Hopf algebras in
question are of the form $(L[N])^{G}$ where $N\leq B=Perm(G)$ is a regular
subgroup that is normalized by the left regular representation $\lambda(G)\leq
B$. We consider the case where both $G$ and $N$ are isomorphic to a dihedral
group $D_n$ for any $n\geq 3$. Using the normal block systems inherent to the
left regular representation of each $D_n$,(and every other regular permutation
group isomorphic to $D_n$) we explicitly enumerate all possible such $N$ which
arise.
