Changing WAN to static IP address and Synology NAS
Sophia Terry 
I have a Synology NAS that connects to my AT&T fiber provided modem/router. I have the NAS assigned a static internal IP address like 192.168.1.70. I also have port forwarding rules setup to allow for a webdav/afp connection to my NAS (LAN @ 192.168.1.70) when I am not at home. My modem/routers’ IP address (WAN-facing) is something like 96.76.152.52. As such I can just go to 96.76.152.52:5000 anywhere in the world and access my NAS’s web interface or connect through webdav via 96.76.152.52:5005 with my credentials. This works fine.
However, 96.76.152.52 is a dynamically assigned IP address from my ISP aka it can change (although according to them it rarely will). I wanted to get a static WAN IP address so my router’s IP @ 96.76.152.52 becomes 100.12.122.19 but never changes again. As such, any device connected to my LAN would see 100.12.122.19 when doing findmyip.
So AT&T only leases static IPs as units of 5. Fine. On the phone with the rep, they were telling me that I had to assign my server one of the static IPs, let’s call it 100.12.122.19 and gave me additional details for the subnet mask, gateway, dns server .etc… This is where I got really confused. Why would I configure my server with these IP addresses? Why isn’t my router’s IP of 96.76.152.52 just changing to 100.12.122.19? So I stopped the process so I could better understand what was going on.
To me, I don’t see how changing my server to 100.12.122.19 with a completely different gateway and dns details than my modem/router would work. How would I even connect to my server when I’m local if the IP address isn’t an internal one like 192.168.1.70. I felt like there was a miscommunication, so I explained my setup to them numerous times and the same thing was told to me.
Can anyone shed light on this? Was the rep simply wrong/confused, or am I missing something?
1 Answer
When offering you the "5 IP's" - AT&T are not replacing your current IP address with a new one, rather they are routing a subnet of IP address across your existing IP address for your router to handle. (They are actually giving you 8 IP addresses, but 2 are unusable and 1 is needed by your router leaving 5 for use on your network.
At the bottom of the link in the page you give us it talks about "Static DSL IP to static internet IP". This will provide a single IP address that behaves as you want. If you can get this without the additional IP's - that is ideally what you want. Your router IP address will become a static one and everything else can remain as is. Its wasteful, but if you only get this with a block of static IPs, you could just ignore the block of IP's and it would work as you expect.
A bit more about these Static IP address blocks which might be helpful :
They are useful if you have multiple servers behind your router.To use them you may require a better router then the standard home user router many people have. (You can do this with some knowledge and a SOHO router that runs more advanced software - like dd-wrt)
To use them your router no longer has just a WAN and a LAN - Effectively your router would now heave a WAN and 2 LANS - the existing LAN (in your case with 192.168.70.x on it) and a second LAN with IP addresses your ISP is providing. When devices on your current LAN - ie 192.168.70.x want to reach devices with a static IP address, traffic will go through the router in one LAN interface and out the other.
I do note that if you have less then 6 devices on your LAN you could simply replace your current 192.168.70.x address with new IP addresses your provider gives you, and reconfigure your router. This is likely a bad idea though as your devices are more exposed to the Internet and a lot more likely to be hacked. (Because your current 192.168.70.x is behind NAT the devices can't be reached through the Internet directly unless you do port forwarding)
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