Hi, Hope this can help someone.
To connect local network storage, mine is DS1817+. Create port forward and connect thru internet.
Do reply here if you have better or easier configuration! =D
Configuration on Cisco Router:
ip nat inside source static udp 192.168.2.99 137 interface GigabitEthernet5 137
ip nat inside source static udp 192.168.2.99 138 interface GigabitEthernet5 138
ip nat inside source static tcp 192.168.2.99 139 interface GigabitEthernet5 139
ip nat inside source static tcp 192.168.2.99 445 interface GigabitEthernet5 445
Guide on configuring your Windows to connect Synology device via SMB.
https://www.synology.com/en-global/knowledgebase/DSM/help/DSM/Tutorial/store_with_windows@ps
Follow the first part of the video on configuring your Synology device port forwarding to the router.
https://www.youtube.com/watch?v=caN6XGJOYRw&vl=en
SMB connection required.
https://support.microsoft.com/en-us/help/3185535/preventing-smb-traffic-from-lateral-connections