  We investigate how T-duality and solving the boundary conditions of the open
bosonic string are related. We start by considering the T-dualization of the
open string moving in the constant background. We take that the coordinates of
the initial theory satisfy either Neumann or Dirichlet boundary conditions. It
follows that the coordinates of T-dual theory satisfy exactly the opposite set
of boundary conditions. We treat the boundary conditions of both theories as
constraints, and apply the Dirac procedure to them, which results in forming
$\sigma$-dependent constraints. We solve these constraints and obtain the
effective theories for the solution. We show that the effective closed string
theories are also T-dual.
