Plain Debian 10 uses the following mechanism to trigger events on link up/down
```
$ cat /lib/udev/rules.d/80-ifupdown.rules
# Allow rfkill for users in the netdev group
KERNEL=="rfkill", MODE="0664", GROUP="netdev"
# Handle allow-hotplug interfaces
SUBSYSTEM=="net", ACTION=="add|remove", RUN+="ifupdown-hotplug"
```
VyOS 1.3 and 1.4 both only have two scripts which get executed on link-state changes:
- [[ https://github.com/vyos/vyos-1x/blob/04724ed189553ce43f8504f68fef8024ef5796de/src/etc/netplug/linkdown.d/dhclient | /etc/netplug/linkdown.d/dhclient ]]
- [[ https://github.com/vyos/vyos-1x/blob/04724ed189553ce43f8504f68fef8024ef5796de/src/etc/netplug/linkup.d/dhclient | /etc/netplug/linkup.d/dhclient ]]
Despite the arguably ancient Perl content, this scripts can also be invoked by a vyos-ifupdown wrapper script or directly. Also the invocation is limited to bridge, ethernet and bond interfaces [[ https://github.com/vyos/vyos-build/blob/f0cbc17bdaa24633cbe0bfb5b0228b8df7e65b26/data/live-build-config/includes.chroot/etc/netplug/netplugd.conf | /etc/netplug/netplugd.conf ]]