Wifi channel issue

[Sherif Hassan]

Dears,

I am experiencing a significant issue with the Cisco Access Point model 'AIR-AP3802I-B-K9,' where certain devices are unexpectedly disconnecting. When attempting to reconnect, the error message 'Cannot connect to this network' appears on Windows. Upon investigating the root cause, I suspect the issue may be related to the wireless channel configuration. I attempted to resolve it by switching the channel to 1, 6, and 11, but the problem persists.

Edit 23/08/2025 09:53 AM

Second Issue, it takes time to join the network, maybe 45 seconds.

I have 5 Access Points, and I'm controlling them by making one Access Point a Controller

Cisco Aironet 3800 Series Mobility Express

Software Version: 8.5.161.0

Radio Policy: All (5GHz - 2.4 GHz) 

Security Type: WPA2 Personal 

Kindly let me know how I can solve this issue. 

Below is the Access Point Configuration.

Regards

[MHM Cisco World]

show wireless exclusion-list <<- I think this client add to exclusion list

MHM

[Sherif Hassan]

Hello MHM,

No, I didn't add him to the exclusion list because there is no exclusion list I have created.

[MHM Cisco World]

It automatically add if client failed to authc multi times

MHM

[Sherif Hassan]

From where can I find this list

[eglinsky2012]

What software version is the AP/WLC running? What type of authentication is on the SSID, is it 802.1x or WPA2-PSK, etc?

If you haven't already, try going to the list of known networks, "forget" the SSID, then reconnect. Also try updating drivers for the WiFi device, and go through the computer or NIC manufacturer for the latest drivers rather than Windows Update.

[Sherif Hassan]

Hello @eglinsky2012 

I tried to do that by forgetting the Network, then re-joining but the problem still exists, and this issue affects most of the employees, not just one user.

Below are the Access Points Configuration:

Software Version: 8.5.161.0

Radio Policy: All (5GHz - 2.4 GHz) 

Security Type: WPA2 Personal 

[Mark Elsen]

 - @Sherif Hassan        What is the WLC  model ?

  M.

[eglinsky2012]

What software version is the AP/WLC running? What type of authentication is on the SSID, is it 802.1x or WPA2-PSK, etc?

If you haven't already, try going to the list of known networks, "forget" the SSID, then reconnect. Also try updating drivers for the WiFi device, and go through the computer or NIC manufacturer for the latest drivers rather than Windows Update.

[Saikat Nandy]

Interesting..!! Few pointers - 
1. What made you think that the issue could be related to the channels?
2. Secondly, why you had to switch the channels to 1,6 & 11? What were the channels before?
3. What's the WLC model and version running?
4. Have you taken any debug client (AireOS) or RA trace (9800) reproducing the issue?

[Sherif Hassan]

Hello @Saikat Nandy 

1- Because I searched for some reasons for this issue, and I got that maybe the interference between the channels causes that.

2- Before it was automatic, but I got the same issue and I searched and I found that the best channels for 2.4GHz are 1,6,11.

3-Cisco Aironet 3800 Series Mobility Express and Software Version: 8.5.161.0.

4-No, if know know how to do that, please let me know

[Saikat Nandy]

thanks for the response.
Even when it was automatic, it should have been using channels 1, 6 & 11 as these are the only 3 non-overlapping channels available in 2.4Ghz.
there are multiple reasons for the disconnections. 2 things I would suggest - 

1. share the output of 'show run-config' for a review (before running the command you should run 'config paging disable')
2. capture debug reproducing the issue. Command is 'debug client <mac addr>'. It will print the output in the terminal session. Wait for the issue to repro and then stop the debugging by 'debug disable-all'.

[Haydn Andrews]

that image shows clients connected to the WIFI, but cant access the internet

Does the client have an IP address? Can it access the default gateway via ping

Can it resolve DNS entries via nslookup

is it all clients, and all APs?

Is it always affecting these clients or intermittent

[Sherif Hassan]

Hello @Haydn Andrews 

No, it doesn't connect because there are two issues here:-

1- The first one takes a long time to join, maybe 45-50 seconds 

2- After taking a long time, it cannot connect as you see, and there is an error message appearing "Cannot connect to this network.".

- Yes, the client has a static IP address, and I have disabled the DHCP.

- No, it cannot because at this time it isn't connected to the network yet.

- Yes, this issue with all Clients and AP.

- Yes, it is always affecting the clients

Here is the configuration

[JPavonM]

First of all, @Haydn Andrews that screenshot shows Windows unable to connect, the other way will be Connected but no Internet connection:

Few points here:

1. Check your Windows laptops have the latest drivers installed for the wireless adapter. Check the support page of the vendor fisrt, and then also check the support page of the manufacturer (in the case of Intel adapters).
2. Why are you using 2.4 GHz band? You can normally find connectivity issues if the band is congested or occupied by interfering devices, thus leading some clients to not connect, or disconnect.
3. Check you WLC/AP code has no bugs that may point to the issues you are suffering.
4. I've suffered weird issues with AP3802 not receiving enough PoE budget thaus making them to randomly disable radios or dropping clients. Check the PoE budget of the AP.
5. Check if your are reaching the maximum re-association failures, thus leading the WLC to blacklist your MAC address for 180 seconds. Re-association failures may happen if the client send multiple EAPOL messages but they don't reach the RADIUS server, or if the client does not receive the responses and restart the asscoiation in a loop. (Check your RADIUS logs) 
6. Check if you have configured the maximum number of clients per AP/WLAN and you are hitting that figure.
7. Check the RSSI/SNR is proper or if the clients are close to the border of the coverage cell.
8. Check your basic/mandatory data rates, this may be setup to a higher value and the clients may be not able to get those rates becuase they are far from any AP.
9. Finally, check if you may be impacted by a DDoS attack. I have found that untrained admins using Meraki APs use to enable wIPS thus making their APs to send dis-association packets to other neighbour networks if they configured the wIPS feature wrongly.