Content of /etc/network in Alpine Linux image

I have an Alpine Linux image installed on a docker container. I was exploring it, and doing ls -lR /etc/network I had this result:

/etc/network/:
total 24
drwxr-xr-x    2 root     root          4096 Jan 16  2020 if-down.d
drwxr-xr-x    2 root     root          4096 Jan 16  2020 if-post-down.d
drwxr-xr-x    2 root     root          4096 Jan 16  2020 if-post-up.d
drwxr-xr-x    2 root     root          4096 Jan 16  2020 if-pre-down.d
drwxr-xr-x    2 root     root          4096 Jan 16  2020 if-pre-up.d
drwxr-xr-x    2 root     root          4096 Jan 16  2020 if-up.d
/etc/network/if-down.d:
total 0
/etc/network/if-post-down.d:
total 0
/etc/network/if-post-up.d:
total 0
/etc/network/if-pre-down.d:
total 0
/etc/network/if-pre-up.d:
total 0
/etc/network/if-up.d:
total 4
-rwxrwxr-x    1 root     root           218 Jan 15  2020 dad

Inside /etc/network/if-up.d/dad I found:

#!/bin/sh
# Block ifup until DAD completion
# Copyright (c) 2016-2018 Kaarle Ritvanen
has_flag() {
    ip address show dev $IFACE | grep -q " $1 "
}
while has_flag tentative && ! has_flag dadfailed; do
    sleep 0.2
done

I’m trying to understand why those folders exist and which is the purpose of dad. I searched on internet, but I didn’t find anything useful. I expected to find something like /etc/network/interfaces, but I can’t understand what’s the purpose of this all. Can somebody explain it?