ftpsync - Mirror Debian and Debian-like repositories of packages
is part of the ftpsync suite for mirroring Debian and Debian-like
repositories of packages. As there are way too many mirrors of Debian to
populate them all from the machine that generates the archive
("ftp-master"), mirrors are organized in a tree-shaped hierarchy.
Thus, every mirror has exactly one upstream from which it syncs, and each
mirror can have any number of downstreams which in turn sync from it.
Debian mirror team.