PermonFLLOP: Parallel implementation of the FETI DDM constraint matrix on top of petsc for the permonfllop package. This paper deals with implementation of the FETI non-overlapping domain decomposition method within our new software toolbox PERMON, combining quadratic programming algorithms and domain decomposition methods. It is built on top of the PETSc framework for numerical computations. Particularly, we focus on parallel implementation of the matrix which manages connectivity between subdomains within the FETI method. We present a basic idea of our approach based on processing local and global numberings of the degrees of freedom on subdomain interfaces.