Power management is on. The router has a setting to set a static ip on the MAC address.
Iwconfig on the pi:
pi@pi3:~ $ sudo iwconfig
wlan0 IEEE 802.11 ESSID:"Telekom-2.4"
Mode:Managed Frequency:2.432 GHz Access Point: 18:90:D8:94:FC:56
Bit Rate=65 Mb/s Tx-Power=31 dBm
Retry short limit:7 RTS thr:off Fragment thr:off
Encryption key:off
Power Management:on
Link Quality=50/70 Signal level=-60 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:199 Invalid misc:0 Missed beacon:0
eth0 no wireless extensions.
lo no wireless extensions.
pi@pi3:~ $
Even so, why it’s still accesible from the outside of the network on the public IP. Power management should turn off the entire internet access, not only local.