1. A computer program product to provide a substitute filter for an existing filter in a router installed in a network, said existing filter being specifically written for said router after said router was installed in said network, said computer program product comprising: a computer readable media; first program instructions to identify based on at least one feature of said existing filter one of a multiplicity of pre-written filters which matches said existing filter; and second program instructions to write the identified one of a multiplicity of pre-written filters into a file for installation in said router to substitute for said existing filter; and wherein said first and second program instructions are recorded on said computer readable media.