iPhone 7 unable to access LAN via 5GHz radio (2.4GHz works)

Hi.

I recently changed the stock firmware on a TP-Link Archer C20 (Router and Wireless AP) to OpenWrt 22.03 and configured it as a "Dumb AP" on my home LAN, as per the instructions on the OpenWrt website.

All my devices seem happy to access the LAN via 2.4GHz radio or 5GHz radio except my Apple iPhone 7. I have plenty of other Apple devices that can connect and see the LAN on 5GHz, although it might be worth noting that they are all older than the iPhone 7.

The first sign that there was a problem was when I moved into the room where the OpenWrt router is located and my phone lost internet connection, although it was still connected to the AP. At this stage, I had configured the 2.4GHz and 5GHz radios with the same SSID, so the iPhone would automatically switch to the 5GHz radio with the same SSID when I entered the room and switch to 2.4GHz when I left and moved away from the AP.

When on 5GHz, my iPhone would be unable to access the LAN, and therefore was unable to get an IP via DHCP. After a long attempt, it would give up and assign itself a 169.254 address. Even if I manually assigned an IP on the iPhone (disabling DHCP client on the iPhone), I was still unable to access any machines on the LAN from the iPhone. Note that the AP is not running a DHCP server, as described in the "Dumb AP" setup instructions from OpenWrt. My gateway (Ubiquiti EdgeRouter) is running the DHCP server.

On the AP's Luci UI, I can see the iPhone connecting on the Network->Wireless "Associated Stations" list, but it cycles between appearing and disappearing on that list (on wlan1, the 5GHz radio).

No other devices have a problem connecting to the 5GHz radio, seeing the LAN and getting an IP from the gateway via DHCP.

I have since assigned a separate SSID to the 5GHz radio, which confirms the the problem in only when connecting on 5GHz, and only with the iPhone 7.

The OpenWrt AP is replacing a dual-band ASUS AP, which the iPhone had no trouble using on 5GHz.

I would appreciate help and ideas to solve this problem. I am stumped.

If you have enabled "WPA2/WPA3 mixed mode" for your 5GHz wifi config on router, try temporarily change it to WPA2 only and set "802.11w Management Frame Protection" to "optional" (or even "disabled").
Also, temporarily set 36 channel for 5GHz wifi.
Let me know if any of this helps.

Thanks Alex. I tried what you recommended, but unfortunately I still have the same problem.

WPA2/WPA3 mixed mode was not enabled on 5G (it was WPA2-PSK).
Setting 802.11w Management Frame Protection to "optional" did not fix the problem (it was "disabled").
Setting 5GHz channel to 36 did not fix the problem.

It seems like connecting to the AP's 5G radio and authenticating is working fine, but bridging from WLAN1 to the LAN is not working for just this one client device, my iPhone 7. It doesn't seem to matter what MAC the iPhone uses (I can turn on the privacy function that randomises the MAC address of the iPhone's 5G radio and the problem remains). My iPad Air 2 has no problem connecting to the AP's 5G radio and getting access to the LAN.

When I test the iPhone 7 connecting to the 5G radio of my Ubiquiti UniFi AP (running stock firmware), it has no problem and can see the LAN 192.16.1.0/24. That AP has mixed WPA2/WPA3 authentication enabled. The problem doesn't seem to be authentication related, as far as I can tell.

My iPhone also had no problems connecting to an Asus 5G AP (stock firmware) and seeing the LAN.

So it's still a mystery why my iPhone works fine with other (non OpenWrt) 5G APs, the OpenWrt 5G AP works fine with other clients, but the combination of my iPhone and the OpenWrt 5G AP does not work (connection and authentication look fine, but iPhone has no access to the LAN).

iOS has a very low, but still non-zero-chance of getting into a half broken config state. At least this happens to me occasionally during some iOS version update. Things like single iOS buttons no longer working or WiFi issues.

just to be sure, that its not due to an iOS broken config, you might also try one of the typical IT crowd actions:

  • resetting iOS network settings
    and/or
  • resetting all iOS settings (careful, there is also a reset all settings+all content, you dont want to pick that)

Thanks Pico.

I tried "reset network settings", but it didn't fix the problem.
I tried "reset all settings", still not fixed.

I might try a full factory reset after backing up my content.

youu can skip the full iOS factory reset. So far if there really were config related issues, resetting settings and network were sufficient from my experience

Looking at OpenWrt System logs for my iPad Air 2 successfully connect to the 5GHz radio (wlan1). MAC has been replaced with XX:XX:XX:XX:XX:XX

Sat Oct  1 16:36:04 2022 daemon.info hostapd: wlan1: STA XX:XX:XX:XX:XX:XX IEEE 802.11: authenticated
Sat Oct  1 16:36:04 2022 daemon.info hostapd: wlan1: STA XX:XX:XX:XX:XX:XX IEEE 802.11: associated (aid 1)
Sat Oct  1 16:36:04 2022 daemon.notice hostapd: wlan1: AP-STA-CONNECTED XX:XX:XX:XX:XX:XX
Sat Oct  1 16:36:04 2022 daemon.info hostapd: wlan1: STA XX:XX:XX:XX:XX:XX WPA: pairwise key handshake completed (RSN)
Sat Oct  1 16:36:04 2022 daemon.notice hostapd: wlan1: EAPOL-4WAY-HS-COMPLETED XX:XX:XX:XX:XX:XX

Now the logs of my iPhone 7, connecting, but not able to access the LAN.
MAC has been replaced with ZZ:ZZ:ZZ:ZZ:ZZ:ZZ

Sat Oct  1 16:41:23 2022 daemon.info hostapd: wlan1: STA ZZ:ZZ:ZZ:ZZ:ZZ:ZZ IEEE 802.11: associated (aid 2)
Sat Oct  1 16:41:23 2022 daemon.notice hostapd: wlan1: AP-STA-CONNECTED ZZ:ZZ:ZZ:ZZ:ZZ:ZZ
Sat Oct  1 16:41:23 2022 daemon.info hostapd: wlan1: STA ZZ:ZZ:ZZ:ZZ:ZZ:ZZ WPA: pairwise key handshake completed (RSN)
Sat Oct  1 16:41:23 2022 daemon.notice hostapd: wlan1: EAPOL-4WAY-HS-COMPLETED ZZ:ZZ:ZZ:ZZ:ZZ:ZZ

Differences:

  1. The first log line for the iPad, "authenticated", is missing for the iPhone.
  2. The second log line for the iPad has "associated (aid1)". The corresponding line for the iPhone has "associated (aid2)"

On the LUCI Wireless Associations list, the working iPad connection to the 5GHz radio shows the following in the "Rx Rate / TX Rate" column:

24.0 Mbit/s, 20 MHz
325.0 Mbit/s, 80 MHz, VHT-MCS 7, VHT-NSS 1, Short GI

The problematic iPhone connection shows:

6.0 Mbit/s, 20 MHz
6.0 Mbit/s, 20 MHz

OpenWrt system log after setting 5GHz security to "No Encryption (open network)" and connecting with iPhone 7, which still fails to see the LAN and get an IP from DHCP server running on the gateway:

Sat Oct  1 22:10:09 2022 daemon.info hostapd: wlan1: STA XX:XX:XX:XX:XX:XX IEEE 802.11: authenticated
Sat Oct  1 22:10:09 2022 daemon.info hostapd: wlan1: STA XX:XX:XX:XX:XX:XX IEEE 802.11: associated (aid 1)
Sat Oct  1 22:10:09 2022 daemon.notice hostapd: wlan1: AP-STA-CONNECTED XX:XX:XX:XX:XX:XX

The lack of an "authenticated" line in the logs for the iPhone connecting to wlan1 (5GHz) from my earlier post seems to have been a red herring. I do see the "authenticated" line in subsequent tests and the problem still remains.

Sun Oct  2 07:06:57 2022 daemon.info hostapd: wlan1: STA XX:XX:XX:XX:XX:XX IEEE 802.11: authenticated
Sun Oct  2 07:06:57 2022 daemon.info hostapd: wlan1: STA XX:XX:XX:XX:XX:XX IEEE 802.11: associated (aid 1)
Sun Oct  2 07:06:57 2022 daemon.notice hostapd: wlan1: AP-STA-CONNECTED XX:XX:XX:XX:XX:XX
Sun Oct  2 07:06:57 2022 daemon.info hostapd: wlan1: STA XX:XX:XX:XX:XX:XX WPA: pairwise key handshake completed (RSN)