@mjp79 

Thanks for reaching out. I understand you are trying to reconfigure your Deco Mesh system (including XE75 Pro and M5 units) for a new FTTH connection with Plusnet, which requires switching from Dynamic IP to PPPoE with credentials, and you are concerned about making these changes without an active internet connection. You also want to know if a full reset of all Deco units is necessary and why you can't make configuration changes when the main Deco is offline.

Here are some important points and troubleshooting steps:

1) Deco App Requires Internet for Configuration Changes:
• The Deco app typically needs the main Deco to be online (connected to the internet) to make most configuration changes, including changing the WAN type to PPPoE and entering new credentials. If the main Deco is not connected to the internet, the app may not allow you to proceed with setup or change WAN settings. This is a known limitation.

2) Setting Up Deco with a New ISP (Plusnet FTTH):
• Connect the main Deco directly to the Openreach ONT (which acts as the modem).
• When prompted during setup, select 'PPPoE' as the internet connection type and enter your Plusnet username and password.
• If you are unable to access the setup process because the Deco is offline, you may need to perform a reset on the main Deco to start the setup process from scratch.

3) Do You Need to Reset All Deco Units?
• If you are changing ISPs and WAN settings, it is generally recommended to reset the entire Deco network and set up a new network from the beginning. This ensures all units are properly configured for the new connection.
• To reset, press and hold the reset button on each Deco unit for about 1 second until the LED blinks yellow, then release. Set up the main Deco first, then add the others.

4) Additional Troubleshooting Tips:
• Make sure only one Deco unit is powered on during the initial setup.
• Ensure the main Deco is connected to the ONT with a good Ethernet cable.
• If you encounter errors such as 'Ethernet Cable is Not Connected' or 'No Internet Connection,' try different cables or ports, and reboot both the ONT and Deco.
• If you have internet on a PC when connected to the ONT but not on Deco, check if MAC Clone is needed (see https://www.tp-link.com/support/faq/2925/).

5) Web Interface Limitations:
• Deco's web interface is very limited and does not allow WAN configuration or advanced settings. All main setup and changes must be done via the Deco app.

6) Further Help:
• For more detailed troubleshooting, refer to: https://www.tp-link.com/support/faq/2239/
• If you continue to have issues, please contact TP-Link support for further assistance.

In summary: Yes, a full reset is usually necessary when switching ISPs and WAN types, and configuration changes require the main Deco to be online. The Deco app is the only way to make these changes, and the web interface cannot be used for WAN setup.

  @mjp79 

Hi, welcome to the community.

Here are some details for your reference:

• Deco also served as a DHCP router in default mode. In other words, the Deco and Plusnet router(is it Plusnet Hub Two?) are substituted.

• "Because the Plusnet router doesn't support or need to support a Bridge mode as the Open Reach ONT acts as the modem. The Virgin router had a "modem" mode."

-Do you want to keep both the Plusnet router and Deco?

Case one:

If you plan to keep the Plusnet router and have already configured PPPOE in the Plusnet router,  you don't need to have a full reset on the Deco, and when the Deco is plugged behind the Plusnet router, it should be plug-and-play.

(If you don't want to have double NAT, you can change the operation mode under Deco APP>More>Advanced>Operation Mode to "Access Point" mode.)

Case two:

If you only want to use Deco, you will need to configure PPPOE on the Deco APP.

After switching to Plusnet and connecting Deco to the Open Reach ONT, there is still no need to do a full reset on Deco, and you can change the Internet Connection type from Dynamic IP to PPPOE under Deco APP>More>Internet Connection> IPv4 Internet Connection type.

(You'll need to connect to the Deco WiFi to make the changes. Deco APP also supports local management, so please don't worry, the Deco WiFi temporarily had no internet access during the ISP switch.)

Wait for your reply.

Best regards.

  @mjp79 

Go with @David-TP answer first he works for tp-link I'm just free labor :)