bridge-utils 1.5-13+deb9u1 / etc / network / if-pre-up.d / bridge

/etc/network/if-pre-up.d/bridge is in bridge-utils 1.5-13+deb9u1.

This file is owned by root:root, with mode 0o777.

It is a symlink to /lib/bridge-utils/ifupdown.sh