dh_installifupdown man page
dh_installifupdown — install if-up and if-down hooks
dh_installifupdown [debhelper options] [--name=name]
dh_installifupdown is a debhelper program that is responsible for installing if-up, if-down, if-pre-up, and if-post-down hook scripts into package build directories.
These files are installed into etc/network/if-*.d/package in the package build directory.
Look for files named debian/package.name.if-* and install them as etc/network/if-*/name, instead of using the usual files and installing them as the package name.
This program is a part of debhelper.
Joey Hess <email@example.com>