如图,在六面体\(ABCD-A_{1}B_{1}C_{1}D_{1}\)中,平面\(ABCD/\!/\)平面\(A_{1}B_{1}C_{1}D_{1}\),\(DD_{1}/\!/\)平面\(A_{1}B_{1}BA\),\(DD_{1}/\!/\)平面\(B_{1}BCC_{1}\).
\((1)\)证明:\(DD_{1}/\!/BB_{1}\);
\((2)\)已知六面体\(ABCD-A_{1}B_{1}C_{1}D_{1}\)的棱长均为\(2\),且\(BB_{1}⊥\)平面\(ABCD\),\(∠BAD=60^{\circ}\),\(M\),\(N\)分别为棱\(A_{1}B_{1}\),\(B_{1}C_{1}\)的中点,求四面体\(D-MNB\)的体积.