Solved: Client getting the IP of the Access Point as DNS

DJay11 · ‎05-31-2023

Some of our access points have problem recovering after a power interruption (No UPS). The clients connected to it are getting the IP of the Access Point as DNS. We need to restart the AP to restore the correct DNS of Clients.

- We have a separate DHCP Server

- AP are connected to Cisco Switch 9200 - PoE

- AP Model is C1920AX1-A

- Controller is Cisco Catalyst 9800-40 Wireless Controller v 17.6.3

- We have 70 Access Points associated in the controller and around 10-15 AP encounter this problem

- We have adjusted the TX power but same issue

Rich R · ‎06-01-2023

1. Update software as per TAC recommended below - 17.6.5 or 17.9.3 currently.

2. Clients can't magically get the AP IP as DNS so most likely some sort of rogue DHCP server handing that out. Either something else on the network or maybe the AP itself is switching to EWC mode with local DHCP? What type of client? On windows "ipconfig /all" will show the DHCP server IP.

3. Are you putting clients and IPs on the same subnet? Ideally you should have a dedicated subnet for managing the APs and clients should be on a separate VLAN.

If EWC is the culprit then you need to disable EWC - via direct AP CLI config, or DHCP option 43 or by removing the EWC software completely using the process at https://www.cisco.com/c/en/us/support/docs/wireless/catalyst-9120axi-access-point/217537-repairing-c9120-c9115-access-points-from.html to totally re-flash the AP.

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Please click Helpful if this post helped you and Select as Solution (drop down menu at top right of this reply) if this answered your query.
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TAC recommended codes for AireOS WLC's and TAC recommended codes for 9800 WLC's
Best Practices for AireOS WLC's, Best Practices for 9800 WLC's and Cisco Wireless compatibility matrix
Check your 9800 WLC config with Wireless Config Analyzer using "show tech wireless" output or "config paging disable" then "show run-config" output on AireOS and use Wireless Debug Analyzer to analyze your WLC client debugs
Field Notice: FN63942 APs and WLCs Fail to Create CAPWAP Connections Due to Certificate Expiration
Field Notice: FN72424 Later Versions of WiFi 6 APs Fail to Join WLC - Software Upgrade Required
Field Notice: FN72524 IOS APs stuck in downloading state after 4 Dec 2022 due to Certificate Expired
- Fixed in 8.10.190.0, latest 9800 releases, 8.5.182.11 (8.5 mainline) and 8.5.182.108 (8.5 IRCM)
Field Notice: FN70479 AP Fails to Join or Joins with 1 Radio due to Country Mismatch, RMA needed
How to avoid boot loop due to corrupted image on Wave 2 and Catalyst 11ax Access Points (CSCvx32806)
Field Notice: FN74035 - Wave2 APs DFS May Not Detect Radar After Channel Availability Check Time
Leo's list of bugs affecting 2800/3800/4800/1560 APs

View solution in original post

Leo Laohoo · ‎05-31-2023

Sounds like CSCvt29946/CSCvv13646.

DJay11 · ‎06-02-2023

We will look into this. Thank you.

Rich R · ‎06-01-2023

1. Update software as per TAC recommended below - 17.6.5 or 17.9.3 currently.

2. Clients can't magically get the AP IP as DNS so most likely some sort of rogue DHCP server handing that out. Either something else on the network or maybe the AP itself is switching to EWC mode with local DHCP? What type of client? On windows "ipconfig /all" will show the DHCP server IP.

3. Are you putting clients and IPs on the same subnet? Ideally you should have a dedicated subnet for managing the APs and clients should be on a separate VLAN.

If EWC is the culprit then you need to disable EWC - via direct AP CLI config, or DHCP option 43 or by removing the EWC software completely using the process at https://www.cisco.com/c/en/us/support/docs/wireless/catalyst-9120axi-access-point/217537-repairing-c9120-c9115-access-points-from.html to totally re-flash the AP.

------------------------------
Please click Helpful if this post helped you and Select as Solution (drop down menu at top right of this reply) if this answered your query.
------------------------------
TAC recommended codes for AireOS WLC's and TAC recommended codes for 9800 WLC's
Best Practices for AireOS WLC's, Best Practices for 9800 WLC's and Cisco Wireless compatibility matrix
Check your 9800 WLC config with Wireless Config Analyzer using "show tech wireless" output or "config paging disable" then "show run-config" output on AireOS and use Wireless Debug Analyzer to analyze your WLC client debugs
Field Notice: FN63942 APs and WLCs Fail to Create CAPWAP Connections Due to Certificate Expiration
Field Notice: FN72424 Later Versions of WiFi 6 APs Fail to Join WLC - Software Upgrade Required
Field Notice: FN72524 IOS APs stuck in downloading state after 4 Dec 2022 due to Certificate Expired
- Fixed in 8.10.190.0, latest 9800 releases, 8.5.182.11 (8.5 mainline) and 8.5.182.108 (8.5 IRCM)
Field Notice: FN70479 AP Fails to Join or Joins with 1 Radio due to Country Mismatch, RMA needed
How to avoid boot loop due to corrupted image on Wave 2 and Catalyst 11ax Access Points (CSCvx32806)
Field Notice: FN74035 - Wave2 APs DFS May Not Detect Radar After Channel Availability Check Time
Leo's list of bugs affecting 2800/3800/4800/1560 APs

DJay11 · ‎06-04-2023

Sending join request to 192.168.1.1 through port 5262 (from AP Logs)

Seems that the AP is connecting to another Controller with 192.168.1.1 with mac address 0000.5e00.0101 (Not our network) with WLC IOS version 17.6.1.13. We got this from the logs of the AP. Note that we only have 1 valid WLC.

The client are still getting the correct dhcp server. The only problem is the DNS IP which is the IP of the AP.

The Client and AP Mangement are on different subnet.

Thank you for this. I have shared all of these to our 3rd party support and TAC.

Great Help.

We already have