/etc/network/ifupdown-scripts-zg2.d/ is in ifupdown-scripts-zg2 0.6-1.
This file is owned by root:root, with mode 0o755.
..
/etc/network/ifupdown-scripts-zg2.d/00README.linkdir
/etc/network/ifupdown-scripts-zg2.d/address
/etc/network/ifupdown-scripts-zg2.d/common-functions
/etc/network/ifupdown-scripts-zg2.d/delstate
/etc/network/ifupdown-scripts-zg2.d/eth-interfacename
/etc/network/ifupdown-scripts-zg2.d/flags
/etc/network/ifupdown-scripts-zg2.d/link
/etc/network/ifupdown-scripts-zg2.d/lo-linkup
/etc/network/ifupdown-scripts-zg2.d/proxy-arp
/etc/network/ifupdown-scripts-zg2.d/redirects
/etc/network/ifupdown-scripts-zg2.d/specialcommands
/etc/network/ifupdown-scripts-zg2.d/staticroutes
/etc/network/ifupdown-scripts-zg2.d/vlan