When you ask for a web site, you ask for a domain name resolution from an authenticating authority. Typically this is your ISP's DNS server, Although you can change this to any of the publicly available ones, like Google's. (8,8,8,8 and 8,8,4,4) This service takes a name, such as http://www.microsoft.com or http://www.asustor.com and converts it to an IP. This IP represents the actual physical address of the machines on the internet or even on your own network.
A dynamic DNS server is one that your device or software you install on a PC or NAS that periodically checks the WAN IP and then goes to a DDNS server and "reports" it's IP to that service. Such as http://www.myasustor.com or http://www.asuscomm.com if you have an Asus brand router. Since the tail end of the name tells the DNS who the main authenticating authority is, it sends that request out to that authority, in this case to myasustor.com or asuscomm.com, depending...
Since yo logged into your NAS with your user ID and registration, etc. You are going to have a free DDNS with Asustor, you just need to turn it on. Then your ID is going to be something like mine... XXXXX.myasustor.com (The X's are replaced with my user IP for the service.) I can get to anything I want on my NAS by forwarding a port and remembering the port number and typing in http://XXXXX.myasustor.com:port#. Each port number is an important part of the address, too... The http (or https) tells the machines involved what type of traffic, in this case web pages, and the XXXXX.,myasustor.com goes to my NAS. But to get to Plex, I need to include the 32400, PlexPy 8181, etc.
The XXXX.myasustor.com is like a phone number, giving country code, state and city. The port number following this ":" actually tells it what the last 4 digits of the phone number is, so to speak. It's telling the server what service you have running on it that you want to access.
The ADM uses port 8000 and 8001. 8001 is for secure or https traffic.
Plex uses 32400 and any additional ports you may have configured in the software.
PlexPy uses 8181 by default.
SABnzb+ uses 8088
Sonarr uses 8989
Couchpotato uses 5050.
So if you want to access all of these services on your NAS from outside of your local network EACH of them will need a Port Forward rule made on the router.
This rule says something like this: Traffic inbound from the world on port XXXX goes to internal IP of the NAS (this is set static on the router for your NAS) like 192.168.1.15. Pulling up the page http://yourIDhere.myasustor.com:8000 should show you the same results as http://192.168.1.15:8000 does. One goes out to resolve the name, the other stays local. This rule basically translates a request on port XXXX to automatically go to device 192.168.1.15, regardless of who it might actually need to go to. So if you have 2 machines running SABnxb+ on your network, a rule for 8088 external forwards to .15 on port 8088 and then 8090 forwards to .16 on port 8088. (This can get a bit tricky, so best not to run more than one service of a given type on your network unless you know WTH you are doing. You can possibly screw everything up and the world will implode...) (OK, maybe not implode...) (Just lots of sparks...) (OK, no sparks, but nothing works right for SABnzb+ on your network until you fix it...)
If you try to use the 192 one when you are at work and your NAS is at home it's going to fail.... 192..... can't be reached.
If you don't forward the port, then going to http://yourIDhere.myasustor.com:8000 is also going to fail as the router doesn't have a route set for that port. (If you turn off NAT and uPnP which every self respecting network guy in the world is going to tell you to do anyway.)
A lot of detail here, and some of it might be old hat. Some of it might be new. If it doesn't make much sense, I suggest reading a bit on internet and the design of it. Wiki is your friend, and so is google. You can search for and read as much as you want from them. I give you the plans to build the boat, but you gotta buy the wood and the screws and put it all together...
I sure hope this rambling makes sense. I'm hot, sticky and tired. It was a long day today..... We set a new temp record and I was running a shovel for a goodly part of it.
My router does not support DHCP on WAN interface.