WiFi AP works, until I change the SSID. How come?

Question

I've followed the excellent instructions at Setting up a Raspberry Pi as an access point - the easy way and have succeeded in setting up my Raspi 3b as a router (Ethernet on the uplink on subnet 192.168.6.0/24, WiFi AP on the internal side with subnet 192.168.8.0/24). Everything is perfect, with an SSID of foo2. However, if I edit the /etc/wpa_supplicant/wpa_supplicant-wlan0.conf file to change the SSID to foo and reboot, nothing can connect. The symptom from the client devices (Android "NETWORK_SELECTION_DISABLED_ASSOCIATION_REJECTION", chromebook "Out of Range", Ubuntu laptop "") is that of an incorrect password. So the foo SSID is visible, and a connection attempt is made, but it fails.

My reason for changing the SSID from foo2 to foo is because I have an existing Ethernet/WiFi router that I'm looking for the Raspi to replace. So once I got the Raspi working, I changed the SSID to that of the old device, which I have turned off.

On the client devices I've tried forgetting the original foo network and reentering the password, but still no joy. All SSIDS (original foo, new foo) have the same password.

        My Router
        /       \        192.168.6.0/24
Old device       Raspi           foo and foo2 both work
  foo             foo2   192.168.8.0/24

______________________________________
        My Router
        /       \        192.168.6.0/24
                 Raspi          foo does not work
                 foo     192.168.8.0/24

I'm seeing WPA: wpa_sm_step() called recursively in the Raspi syslog. I also think I saw that the log file in my failing dhcp-client contains references to the wrong mac address. So maybe there is an ARP cache issue somewhere in the dhcp implementation.

Answer 1

As you say the error message is that of an incorrect password, I was told by another user that he had problems with the length of the password. Could this also be an issue for you? A password with 8 characters definitely works. Maybe your old device accepted shorter passwords. I have also heard about difficulties with quoting the ssid and/or password string so you could try to change these settings. Maybe the ssid must be at least 4 character (don't believe it really)?

For further troubleshooting I would run both access points, the scenario that works. Then associate all stations to foo2 and then switch off foo. If this works then just rename foo2 to foo.

The chromebook reports "Out of Range" so it may be an issue because the RasPi has a lower range.

DHCP could also be an issue. Following the instructions to Setting up an access point and with eth0, with routing then you have enabled the DHCP server build in systemd-networkd with the configuration in /etc/systemd/network/08-wlan0.network. This is meant to be lean and simple and just doing the most needed functions out of the box. Look in man systemd.network at [DHCPSERVER] SECTION OPTIONS what options you can set. With PoolOffset=, PoolSize= you can define the address range that is available to DHCP clients. But you cannot define the DHCP server to be authoritative for the broadcast domain. That's to much for this simple DHCP server. Maybe it is it by default? If you want this option you should use isc-dhcp-server.

I have setup an access point from scratch with this settings:

rpi ~$ sudo cat /etc/wpa_supplicant/wpa_supplicant-wlan0.conf
country=DE
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

network={
    ssid="foo"
    mode=2
    key_mgmt=WPA-PSK
    psk="secretpasw"
    frequency=2412
}

This worked with a debian laptop and an android mobile phone. It may also be an option for you. Switch off the old device, setup the RasPi and associate your stations to it.

Another point could be random numbers. For encrypting keys for secured connections wpa_supplicant needs random numbers. Generating this is very slow on a Raspberry Pi. If it does not have enough entropy to generate encrypting keys wpa_supplicant will reject the authentication. You can look with cat /proc/sys/kernel/random/entropy_avail how many entropy is available. It should be >1000 to work quick enough. Fortunately the RasPi has a True Random Number Generator (TRNG) in hardware. You can use it if you install the service supporting this with:

rpi ~$ sudo apt install rng-tools