In APP Configuration Errors when setting up Guest Network/changing SSID of 2nd and 3rd bands

Question

Background:&nbsp; Originally setup system in 2021 and have had no issues since.&nbsp; Power surges in neighborhood this week caused a factory reset (or something similar), all my customizations were lost.&nbsp; In trying to re-customize back to the 3 custom SSID's and guest network, I kept getting a "Configuration Error".&nbsp; I have done a reboot and also a hard factory reset.&nbsp; I was able to get my primary band SSID custom rename back after a full reset and re-installation with the App, however when I try to custom name the other two bands, or create a guest network, the APP keep spinning, or immediately says "Configuration Error."&nbsp; No other coding or info is being relayed by the APP.&nbsp;Additional Info:Model R8000P Tri-BandRouter. Firmware: V1.4.4.94&nbsp; App Version 2.27.0.77I use a CenturyLink Modem to bring in high speed Internet.&nbsp; ALL SSID's are hidden and turned off of CL Modem so the only thing it does it it is hard cable the Internet directly into the Nighthawk Modem.&nbsp; This worked perfectly for more than two years so I understand how to configure these joint systems.&nbsp;What I don't understand is what happened this week where the Netgear router chose to remove my custom SSID settings, and now won't let me recustomize.&nbsp; When I did the factory reset, it checked for hardware updates and it says it is up to date.&nbsp; With the reset, it did let me create a custom name for the first 2.4Ghz band, and yet when I try to configure the other two bands and the guest network, it just says "Configuration Error."&nbsp;I've read all the Support materials and checked the community already.Anyone have any ideas please?&nbsp;&nbsp;

michaelkenward · Answer

DalySio&nbsp;wrote:
I use a CenturyLink Modem to bring in high speed Internet.&nbsp; ALL SSID's are hidden and turned off of CL Modem so the only thing it does it it is hard cable the Internet directly into the Nighthawk Modem.&nbsp; This worked perfectly for more than two years so I understand how to configure these joint systems.
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Turning off the wifi does not disable the router bit of your modem/router. So you are piling router on router, a recipe for chaos.
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The fact that it worked before just means that the two devices configured themselves to coexist at some stage. If you have a backup of those old settings, then you could try restoring them. Failing that you are going to have to take the whole network through the setup process in the correct order.
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The first thing to do is to forget about using an app to set up your network. This gives much less control than the browser graphical user interface (GUI).
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Then you need to address the "two routers" issue.
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Two routers on your network can cause headaches. For example, you can end up with local address problems. Among other things, the other router can misdirect addresses that the Netgear router usually handles, such as routerlogin.net or the usual IP address for a router, 192.168.1.1.This explains some of the other drawbacks.What is Double NAT? | Answer | NETGEAR SupportUnless you have specific reasons for using two routers – to create two separate networks for example – it is often easier to use just one router and then to set up the second router as a wifi access point. Netgear advises this, as does just about every site you will visit.It may be possible to put the modem/router into modem only (bridge) mode and then to use the second device as the router. 
I've read all the Support materials and checked the community already.
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I'm surprised that you missed the "double NAT" mentions. It usually crops up several times a day.

DalySio · Answer

Thank you for your detailed reply.&nbsp; When I set it up I was very careful to deactivate anything with the CL Modem that effectively was its router function, and unfortunately I didn't take any notes about what I did to effectively make it work great for almost 3 years.&nbsp;I agree that there's a possibility of NAT errors and was hoping I wouldn't have to start from scratch but that may be what I need to do.&nbsp;&nbsp;&nbsp;Again, I appreciate your comments.

Kitsap · Answer

Does your Century Link Modem/Router device have a model number?&nbsp;Does your internet service come over a DSL connection?&nbsp;&nbsp;

DalySio · Answer

CL Modem is a C2100T.&nbsp; It's an older model but we 100% own it.&nbsp; It became too slow as a router which is why I reconfigured it for modem only and bought the Nighthawk.&nbsp;We have high speed fiber, not DSL.We're very happy with our CenturyLink service and speed since they installed the fiber.

michaelkenward · Answer

DalySio&nbsp;wrote:
When I set it up I was very careful to deactivate anything with the CL Modem that effectively was its router function, and unfortunately I didn't take any notes about what I did to effectively make it work great for almost 3 years.
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That is not normally how you "bridge" a modem router. It is impossible to disable everything associated with being a router. Hence the "NAT" hangover.
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Deactivating things and adding a router may have done no more than prompting the new router to adapt its settings to work alongside the other router. Some Netgear routers can do this.
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If you subsequently play around with the router, it may break those settings.
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What you really need is a "mode" setting that disables all the router features. Not all modem routers have this option.
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Your C2100T is a cable modem/router. It looks like it has a genuine bridge mode:
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c2100t bridge mode - Google Search
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Rather than trying to track down your long forgotten settings, the best strategy would be to do what Netgear, and most experienced users here, advise and to bridge the modem/router and then to set up the R8000P from scratch.
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When you have done that create a backup of the router's settings so that the next time you have problems you have a fall back to restore.
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How do I back up the router configuration settings on my Nighthawk router? | Answer | NETGEAR Support
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In APP Configuration Errors when setting up Guest Network/changing SSID of 2nd and 3rd bands

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