2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/179735We present a critical review about the study of linear perturbations of matched spacetimes including gauge problems. We analyse the freedom introduced in the perturbed matching by the presence of background symmetries and revisit the particular case of spherically symmetry in n-dimensions. This analysis includes settings with boundary layers such as brane world models and shell cosmologies.18 pages, plain LaTeX fileGeneral Relativity and Quantum Cosmologytext