Deco M9 Plus (V2) Guest Wi-Fi DHCP Failure with Wired Backhaul (Firmware 1.9.1)
⚠️ Critical Issue: Deco M9 Plus (V2) Guest Wi-Fi DHCP Failure with Wired Backhaul (Firmware 1.9.1)
Since upgrading my TP-Link Deco M9 Plus (V2) mesh system, the Guest Wi-Fi network is failing to assign DHCP addresses (IP addresses) to connecting devices when the units are configured for Wired Ethernet Backhaul. This represents a severe regression from the previous working firmware version.
Specifics of the Problem
| Detail | Specification |
| Deco Model | Deco M9 Plus V2 |
| Problematic Firmware Version | 1.9.1 Build 20250612 Rel 45690 |
| Previous Working Firmware | 1.8.5 |
| Configuration | Wired Ethernet Backhaul (connecting [Number] Deco units) |
| Impact | Devices connecting to the Guest Wi-Fi fail to get an IP address via DHCP. Devices are stuck on "Obtaining IP Address" or receive a self-assigned/APIPA address (e.g., 169.254.x.x). |
| Main Wi-Fi Status | The main (non-guest) Wi-Fi network functions normally with wired backhaul. |
Confirmation of Regression
The issue is definitively linked to the new firmware and the Wired Ethernet Backhaul configuration:
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The network was operating without issue on Firmware 1.8.5 with the exact same wired setup.
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Switching the system to Wi-Fi Backhaul immediately resolves the Guest Wi-Fi DHCP failure, confirming that the network hardware and core DHCP server are functional.
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The problem recurs immediately upon switching back to Wired Ethernet Backhaul.
This strongly suggests a bug introduced in Firmware 1.9.1 affecting the way the Guest Network's isolation or routing function interacts with the Wired Backhaul.
Action Requested: Please investigate this regression in firmware 1.9.1 Build 20250612 Rel 45690 and provide a fix or a known workaround for the Deco M9 Plus V2 model.
