[Solution] ASUS AiMesh: Ethernet backhaul still works with firmware mismatch — leave “Ethernet Backhaul Mode” OFF! (Tested on RT-AX86U Pro + RP-AX58)

[muckipup]

Background

Many users (myself included) have struggled with AiMesh instability or node detection failures after upgrading their main router to the 3.0.0.6 (“3006”) firmware branch, while their AiMesh nodes are forced to remain on the older 3.0.0.4 / 388 branch.

Typical scenario:

• Router: RT-AX86U Pro or similar, now on 3.0.0.6.102_34406
• Node: RP-AX58 (or similar extender/router) stuck on 3.0.0.4.388_24694
• Connection: direct Cat 6 Ethernet between router LAN → node WAN

The mismatch between the newer AiMesh 3.0 protocol (in 3.0.0.6) and the legacy AiMesh 2.x/3.0 handshake (in 3.0.0.4) causes pairing problems:

When “Ethernet Backhaul Mode” is ON, the router never discovers the node at all.

ASUS’s UI wording implies this setting must be ON for wired setups, which has led to confusion across Reddit, ZenTalk, and SNBForums. In fact, enabling it with mismatched firmware branches prevents discovery completely.

The test setup

• Router: RT-AX86U Pro (3.0.0.6.102_34406)
• Node: RP-AX58 (3.0.0.4.388_24694)
• Connection: direct Ethernet (no switch)
• Setting: AiMesh → System Settings → Ethernet Backhaul Mode = OFF

Observed behaviour

1. Ethernet Backhaul Mode = ON → node never detected.
   
   The router expects the 3.0.0.6-style discovery signature and rejects the RP-AX58’s older 3.0.0.4 response.
2. Ethernet Backhaul Mode = OFF → node discovered immediately via Wi-Fi.
3. Once joined, AiMesh automatically detects the live Ethernet link and switches the uplink to “Ethernet (1 Gbps)”, even though the toggle remains OFF.
4. The RP-AX58’s Network tab confirms:
   
   • Double green line between router and node on Asus UI demonstrating ethernet connection
   • Uplink Type = Ethernet (1 Gbps)
   • Backhaul Information = Ethernet + router MAC
   • LAN speed test (iperf3) ≈ 930 Mbit/s ↔ true wired throughput.
     
   Confirmed outcome

Even with firmware mismatch:

• Leave Ethernet Backhaul Mode = OFF.
• Allow pairing over Wi-Fi.
• Keep the Ethernet cable connected.
• After joining, AiMesh seamlessly promotes the backhaul to wired.

The “Ethernet Backhaul” toggle controls discovery policy, not live-link enforcement.

Once the link is detected, AiMesh uses it automatically, even across branch versions.

Why this isn’t widely known​

Most forum guidance assumes identical firmware branches, where the toggle behaves as intended.

When branches differ (3.0.0.6 ↔ 3.0.0.4), the newer router’s discovery handshake rejects the older node if “Ethernet only” is forced — which looks like a cabling fault.

In reality, it’s just a protocol mismatch.

This nuance isn’t documented by ASUS and doesn’t appear in release notes, so users end up chasing “bad cables” or “defective nodes” when the fix is simply turning the toggle off.

TL;DR​

For mixed-firmware AiMesh (router 3.0.0.6 + node 3.0.0.4/388):

• Leave Ethernet Backhaul Mode OFF.

• Pair via Wi-Fi.

• The node will auto-switch to Ethernet (1 Gbps) once the link is detected.

• Verified on RT-AX86U Pro (3.0.0.6.102) + RP-AX58 (3.0.0.4.388_24694).

 

[bbunge]

Well, we have been recommending the Ethernet Backhaul Mode be left off for quite a while. Even with matched firmware.
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[jplw]

I had the same problem, but hve always had Ethernet backhaul mode off. Is it possible thast adding a 3.0.0.4 node turns it on? I did not check for that.

 

[drabisan]

I may be using AiMesh for too long, but early days it was documented discovery is only done over Wifi.
I build a setup where the 2 devices couldn't seen eachother over wifi. And ethernet cable in between didn't help at all. I had to bring node close.
Older firmware, agree. But even when I rebuild my own on 3.0.0.6 I only turned on Ethernet Backhaul after adding the node and validating the 10G link is good.