Yes, that is a known problem. The only operations allowed from a NIS client side on the netgroup table are the ypmatches, but not ypcat (i.e. no support for yp_first(), yp_next() or yp_all() calls). The netgroup table is kind of unique in this. The reason for this is that the netgroup table format changed quite significantly in NIS+ and the NIS+ server would take a big performance hit in converting the netgroups table to YP (key-value) format.