Windows DHCP option 43 not working
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07-25-2023 03:31 PM
Access Point keeps registering to the wrong WLC, ignoring the WLC I specified in option 43. I confirmed the HEX value is correctly entered on the DHCP server using multiple generators. Any suggestions?
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07-25-2023 03:33 PM
What is wlc platform you have?
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07-25-2023 03:41 PM
Hi @tachyon05
It may depend on the DHCP server. The option 43 does not work the same way in all vendor. The other option you have is add the WLC on the AP manually by using the command
capwap ap {primary-base | secondary-base | tertiary-base}controller-name controller-ip-address
You can also add the WLC you want on the Internal DNS. AP always try to resolve the URL CISCO-CAPWAP-CONTROLLER
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07-25-2023 03:50 PM
I have 9800 WLC, and it looks like putting "00" in front of the HEX value doesn't make any difference.
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07-25-2023 03:56 PM
Can I know hex you use as op43?
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07-25-2023 05:02 PM
Still waiting
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07-25-2023 05:04 PM
I used these 2 generators to produce the HEX value, and they produce the same result. I tried with and without the leading 00 since some people said leading 00 are needed for Windows DHCP. I also set the AP to factory default using the WLC GUI, but the AP still registers with the wrong WLC.
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07-25-2023 05:05 PM
What is hex and what tlv you use in dhcp server ?
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07-25-2023 05:13 PM
If you select correct tlv (043) and use correct hex for IP' then last thing prevent ap from choosing wlc in dhcp it have IP of old wlc which have priority than new one learn via dhcp.
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07-25-2023 07:02 PM
What is the HEX value?
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07-25-2023 07:07 PM

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07-26-2023 06:26 AM
Cisco option 43
F1 (addresses x4)(Address in hex)
lets take a single address of say 10.20.30.40, so your code would be
F1040A141E28
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07-26-2023 08:48 AM
Thanks Everyone. Using the 10.20.30.40 IP as an example, both generators I linked above produced the same result "F1040A141E28". This suggests the generators are working correctly. I am not sure what is TLV. On Windows DHCP server, I enabled and added option 43 just like I would for option 150 for TFTP server for phones. The only difference is you can enter IPs in ASCII for option 150.
How do I make my AP forgot the old WLC?
Sorry, but I do not wish to disclose the HEX value.
Thanks for your understanding
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07-26-2023 09:20 AM
Ok' we get your point'
Can you share screen shoot the window Server config you use.
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07-27-2023 05:32 AM - edited 07-27-2023 05:33 AM
The only way to work out how/why the AP is doing that is from the full console log of the AP from power-on. That will tell you exactly what it learns and what decision it makes.
Since you refuse to share any useful diagnostics we cannot help you with interpreting that so you will have to do that yourself.
Keep in mind that AP HA settings will *always* override option 43.
If the AP fails to join the option 43 WLC for any reason (there can be many) then it will try all the others it remembers and can discover (using all possible discovery methods). Again console log will reveal this.
Good luck but if you want more detailed technical help you'll have to provide more technical detail.
You can of course share info with key details obfuscated.
> How do I make my AP forgot the old WLC?
Factory default reset
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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