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According to this document, you need to open UDP 1024 - 65535 between WLC (source) and APs (dest).

And it's correct - I can see these sessions getting dropped on my firewall since I didn't open those ports.

I only opened CAPWAP 5246-5247 from AP to WLC, and it seems to be working just fine. I can see my APs on my WLC, and configuration changes work.

So my question is : what is the WLC trying to send to my APs with those new UDP sessions ? I cannot find any information anywhere, and cannot run a packet capture.

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    – Ron Maupin ♦
    Dec 31, 2020 at 3:54

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It's right there in the footnote:

Arbitrary port number is assigned to every AP from range 1024 - 65535 when the AP joins the WLC. The WLC uses the number as the Destination Port for CAPWAP Ctl/Data as long as the AP is connected.

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  • If I made this post, that's exactly because I did not understand the footnote. What is the session established by the AP used for then ?
    – pHeoz
    Nov 9, 2020 at 15:18
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The WLC uses the number as the Destination Port for CAPWAP Ctl/Data [...]

In this context "Ctl" (Control) is the management traffic between the A.P. itself and the controller (pushing configuration, gathering information, firmware updates, etc...), and "Data" is the data streams from the wireless clients connected to this A.P.

So when the A.P. contact the WLC at startup, a CAPWAP tunnel is establish between them, on a random UDP port.

All communication between the AP and the WLC as well as all traffic from the wireless clients to the other parts of the network are encapsulated in this capwap tunnel.

Note: you can configure the WLC so the client traffic is locally switched by the A.P. but this mode has some drawback. In this case, only the control traffic will use the CAPWAP tunnel.

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  • That's my entire point : the AP creates a CAPWAP tunnel to the WLC. But once this has been established, the WLC attempts to communicate to the AP on a new, unrelated session ! That means traffic is getting dropped on the FW because I did not allow WLC (source) => AP (destination). I'm trying to understand why the WLC behaves like that.
    – pHeoz
    Nov 9, 2020 at 18:54

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