[ASUS RT-AC58U] No IPv4 on WAN interface - OpenWrt 25.12.1 (Regression)

Installing and Using OpenWrt
1

Hi everyone,

I'm experiencing a persistent issue with the WAN interface on my ASUS RT-AC58U (v1, IPQ4018) after upgrading to OpenWrt 25.12.1 (Kernel 6.12.74). The router fails to obtain an IPv4 address via DHCP on the WAN port, although it worked perfectly on the 24.10.x branch.

Symptoms:

  • The wan interface (DSA, wan@eth0) shows as UP with the correct MAC address.
  • udhcpc stuck in broadcasting discover loop and ends with no lease, failing.
  • The same behavior occurs when running udhcpc directly on eth0.
  • Physical link is detected, but no IPv4 traffic seems to pass through to the CPU.

What I've already tried:

  1. Verified MAC address (matches ISP binding).
  2. Set clientid to 0 and tried empty Client ID to avoid Option 61 issues.
  3. Disabled Software/Hardware flow offloading.
  4. Disabled VLAN filtering on the wan device.
  5. Tested with and without "Broadcast flag" in DHCP settings.

Technical Data: ip link output:

wan@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP qlen 1000
    link/ether 78:44:76:fe:d3:95 brd ff:ff:ff:ff:ff:ff

udhcpc manual attempt:

root@OpenWrt:~# udhcpc -i wan -n -q
udhcpc: started, v1.37.0
udhcpc: broadcasting discover
udhcpc: broadcasting discover
udhcpc: no lease, failing

It seems like a regression in the qca8k-ipq4019 switch driver or Device Tree mapping for this model in the 25.12 branch.

Is anyone else seeing this on IPQ40xx devices? Any suggestions on how to debug the DSA switch further would be appreciated.

2

The solution can be found here: Problem with DHCP client and forced ClientID in v25.12