ftp servers referenced from data.gov metadata (count is many urls on each server are in the data.gov metadata):
901441 "rockyftp.cr.usgs.gov"
259 "ghrc.nsstc.nasa.gov"
185 "acdisc.gsfc.nasa.gov"
158 "ftp2.census.gov"
119 "podaac-ftp.jpl.nasa.gov"
73 "gpm.nsstc.nasa.gov"
71 "airbornescience.nsstc.nasa.gov"