We study the conductance of metallic carbon nanotubes with vacancies a
nd pentagon-heptagon pair defects within the Landauer formalism. Using
a tight-binding model and a Green's function technique to calculate t
he scattering matrix, we examine the one-dimensional to two-dimensiona
l crossover in these systems and show the existence of metallic tube j
unctions in which the conductance is suppressed for symmetry reasons.