  The s+- state in which order parameter has different signs in different bands
is a leading candidate for the superconducting state in the iron based
superconductors. We investigate a Josephson junction between s and s+-
superconductors within microscopic theory. Frustration, caused by interaction
of the s-wave gap parameter with the opposite-sign gaps of the s+-
superconductor, leads to nontrivial phase diagram. When the partial Josephson
coupling energy between the s-wave superconductor and one of the s+- bands
dominates, s-wave gap parameter aligns with the order parameter in this band.
In this case the partial Josephson energies have different signs corresponding
to signs of the gap parameters. In the case of strong frustration,
corresponding to almost complete compensation of the total Josephson energy, a
nontrivial time-reversal-symmetry breaking (TRSB) state realizes. In this state
all gap parameters become essentially complex. As a consequence, this state
provides realization for so-called \phi-junction with finite phase difference
in the ground state. The width of the TRSB state region is determined by the
second harmonic in Josephson current, ~ sin(2\phi), which appears in the second
order with respect to the boundary transparency. Using the microscopic theory,
we establish range of parameters where different states are realized. Our
analysis shows insufficiency of the simple phenomenological approach for
treatment of this problem.
