  We study the efficiency of DUNE, a next generation long baseline oscillation
experiment to resolve two major unknowns in neutrino oscillation physics. These
are, octant of $\theta_{23}$ (i.e. if $\theta_{23}$ is $< 45^\circ$ or
$>45^\circ$) and Dirac CP phase $\delta_{CP}$. We mainly focus on the role of
antineutrinos when they travel 1300 km baseline of DUNE. We observe that for
DUNE, the antineutrino runs help to remove parameter degeneracies even in the
parameter space where the antineutrino probability suffers from various
degeneracies. We study these points in detail and find that, due to enhanced
matter effect longer baseline experiments create an increased tension between
the neutrino and the antineutrino probabilities which helps to increase total
sensitivity in case of combined runs. We also find that, antineutrino run
increases overall CP sensitivity due to its ability to abolish
octant-$\delta_{CP}$ degeneracy.
