Deco M9 Plus (V2) Guest Wi-Fi DHCP Failure with Wired Backhaul (Firmware 1.9.1)
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.
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Actually tried to install it. The same file is available on the non-us en forum.
Looked into the binary that v2.2 is supported by it, but apparently the device rejects the file based on same version number and ignores the build and release information.
No error though, looks like everything goes smoothly but fw version stays the same after reboot.
Based on thread https://community.tp-link.com/en/home/forum/topic/796490
the issue is really widespread when we now know the keywords to look for.
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