@jumbo125 The guy setting up the router doesn't seem to know what he was talking about fully. 

Who is your service with?

What they need to do is set their router into bridged mode. Not routed mode. Then you will be able to put the static IP in your Deco and it would work.

A small few ISP's like AT&T demand that you use their gateway and say it can't be removed. But you should ask two questions to someone that knows what they're talking about:

1- Is it absolutely required that I have your router in the mix? Or can we remove it and I only use mine?

2- If they insist you must use theirs in the mix then back to what I said, you need to have them put their router in bridged mode.

This makes theirs stop acting as a router and it will just pass the traffic through and let your Deco be the main router.

The first option is the best. The second is alright. And if they tell you they can't set their router into bridged mode, or maybe they call it pass through mode or even DMZ+ for AT&T... (or they dont understand what those mean) then they probably don't know what they're doing and you might want to ask for a higher tier. 

Btw, the reason your static won't work is because the ISP's modem is using it on its WAN interface, then it is using NAT (since it's in routed mode) and it will assign something like a 192.168.1.1 address to your Deco's WAN interface I can almost guarantee. (Yep, you just said this in your post so all I said is going to be valid and true).

Then you would have to create a different internal network scheme for inside your Deco (LAN) such as 192.168.1.x or 192.168.5.x or whatever. This would be for the internal, aka LAN side. Deco then would be given 192.168.0.1 (by their router... since your Deco WAN is set to DHCP/Dynamic)..
 

If they're the same it's going to clash and cause problems.

This is a situation called double NAT and it's not ideal, because if you're running anything inside that requires a port forward or similar; say you're running a web server or something on a certain port, it's probably not going to pass the traffic unless you do all the same stuff in the other router as well and it just gets to be a headache.

i would also make sure you cut off the wifi on their router if it has it so it doesn't cause interference with your Deco signals.

so- until they can make any changes with their gear you just leave Deco WAN/internet port as dynamic and let it take 192.168.0.1... and then go into "LAN IP" and a set that to 192.168.1.1.

it should automatically adjust DHCP range to 192.168.1.50 to 192.168.1.200 or whatever range. After those things are set you should probably reboot and it should work for the time being.

You would then call the ISP and have them do the bridged mode like I said and then you will have to change your "internet connection" to static mode and use your static info. Once you do that you could leave the LAN IP stuff as 192.168.1.1 no need to change that.

And I would make this final comment - once you're online with what I just said, you probably do have a static IP it's just on their router. Go to something like whatismyip (dot com) or ipchicken (dot com) and you should see it report your static. 
 

Depends why you wanted a static IP. If you just want it to be the same for some reason then you really can leave it be with the double NAT.

If your reason is to set up a web server, gaming server... use VPN stuff or media streaming from outside your network and connect to a machine inside your home... then you're probably going to find it doesn't connect up properly or has other issues and I would absolutely try to do the first two ideal options to make sure it works as you want.

Hope that helps you. Let me know if you have any more questions.

  @YourStupid 

I'm get my internet from the A1 provider in Austria.

The technical team said to me, that they only can setup the router in Router-Modus or in NAT-Mode.

When they set it to Nat-Mode, the Mainrouter will set the DHCP and i can use the Deco as access point. 

When thy set it to routing-Modem the Maintrouter get the intertnet via the wan port and routing it to the next router (Deco, or pc, or what else....)

So... if the mainrouter is set into routing mode, and i conect my laptop via lan with the mainrouter i need to setup my pc with a fix ip. that ip need to be the same, like my satic public ip. the gatway ist the mainrouter static-ip.

When i fill in this infos, the pc get internet an all work. The technic man said, i need to set a firewall or a router or something else after the mainrouter and i need to setup a fix ip. Only when the devices have this fix ip, the mainrouter routing the internet on it.

  @jumbo125 

When you setup the the deco with static ip and with IP-adress 80.120.xx.xx, does the Deco show it can access Internet?

When you connect a device to the Deco, can that device access Internet?

Where do you see that the ip-adress of the deco is 192.168.0.1?

Do you see that in the "Internet Connection" ?

The Deco (in Router mode) has two distinct addresses, and they must be different: 

1. one address on the Internet side, and it should be 80.120.xx.xx.  That is configured on the Deco via "Internet Connection".
2. one address on the LAN side, for your domestic network, and 192.168.0.1 looks like a perfect address for that side.

  @YourStupid I believe this is just a confusion caused by the translation from German to English.
The ISP box is currently configured in "bridge" mode, without DHCP.

  @yves_b here is the problem.

when i set the static ip to 80.xxx.xx.xx and the gateway also static to 80.xxx.xxx.xx the deco doesn't have internet. and when i open the deco in the app, i see, that the ip is: 192.168.0.1. i can read it "under" the mac adress.

  @jumbo125 Ok, I see now.

" when i open the deco in the app, i see, that the ip is: 192.168.0.1. i can read it "under" the mac adress." 

Please let us know where you see this 192.168.0.1 address at. This is important. If it's on the main Deco node screen below description and MAC address then that should be fine... but let's continue with this below anyway.

It sounds to me like maybe DHCP isn't working or the Deco is possibly in access point mode..?

So I will say this again so I am sure to understand.

When you hook the laptop up to the provider device, you cannot access the internet until you put in the 80.x.x.x numbers as a static IP, yes? And it succeeds?

So as @yves_b says, there are two different types and areas for IP, local or LAN and internet or WAN.

Let's see this— 

Go into the TP Link app. Go to More... then Internet Connection.

IP4 Connection... type should be static IP. Put in the 80 address here, the subnet that your provider gave you, and the gateway. The gateway IP is usually close to the same as the static IP but the last number is a few lesser. So IP may end in 87 and the gateway may end in 86 or 85, usually. 
 

So make sure that is all correct.

For DNS, if they gave you two of them, put their first one in the 1st box. For the second DNS, use Google to test... so put 8.8.8.8 there. 
 

This checks in case they have DNS issues we have a more reliable backup one. Then we save.

Next we go to More again.. then Advanced.

We need to make sure the mode is set to Router mode and not Access point or we will have problems.

Save.

Next we go to LAN IP and just to be safe, let's try using 192.168.5.1 as the address and 255.255.255.0 for subnet.

Save.

DHCP server now under More.

Check that this is under the same range as the last setting, so this should be 192.168.5.50 to 192.168.5.200 or close. Last numbers not super important but need to start after 1 (since x50 is using .1) and maybe end at 250?

You can also test DNS by putting the same DNS here as you did in the section above. 
 

Save all, unplug the laptop..

Make sure Deco is now plugged into the provider equipment and then restart Deco. 

Also make sure the laptop itself is changed OFF of static and the 80 address is removed from that. It needs to be set to automatic/DHCP/dynamic again or it will try and use the same IP as your Deco, and will not work. We want the Deco to tell the laptop what it wants the laptop address to be, we don't want the laptop telling the Deco. This is why we set laptop to automatically get an address and we have the Deco in router mode and not access point mode. If it is in access point mode, the laptop will not be getting an IP and you will not get online. 

Test and see. Are you online now?

If all of this does not work still, we can try one last thing and set "Ignore ping from WAN" to off. We want to try allowing it for testing. 
 

If none of this works there is something strange going on. This should work. Next step we may try to reset to factory condition (the Deco) and set this up from the start using the same above settings. 
 

Let us know the results.