A network interface apparatus for connecting incoming and subscriber coaxial transmission lines and having a coaxial transmission line surge arrestor connected in series between the coaxial transmission lines, the surge arrestor comprising a gas discharge tube having a hollow conductive housing and a center conductor having a longitudinal axis parallel to the direction of signal transmission, the interior surface of the hollow housing and the exterior surface of the center conductor being symmetric with respect to the longitudinal axis, ratio of the inner diameter of the conductive housing to the outer diameter of the center conductor being varied within the gas discharge tube for matching the impedance of the surge arrestor to that of the transmission line.