Wireless Access

Hi Guys

Something came to my attention recently after an update, and after some investigation, I came to the bottom of it.

After an AP reboot / Upgrade, the command "show ap bss-table" shows several 5 GHz bss, but it cannot be seen by clients. After some time (about 5-6 minutes) the ssid can be seen.

After asking around, some members of my team said they experienced the same, but only with 5 GHz SSID. And, it seems like it is like that from an 8.6 version onwards.

Did anyone experience something similar or has an explanation for it? Because, if I remember correctly, because of regulatory, the 5 GHz must wait and scan for one minute and then goes up contrary to the 2.4 GHz Band.

We're running a standalone Wireless controller with now version 8.6.0.3, but some colleagues also saw it on MM/MD constructs as well.

Best Regards

Have you tried removing DFS channels from the regulatory domain configuration? Do you have any system logs that point to a delay in the 5Ghz BSSIDs from coming up?

Hi Dustin

No, I have not tried that. But as I said, this should not take this long, even with DFS enabled. Maybe I can give it a try.

No, there are no log entries pointing to something connected to this. That's why I am here, asking you guys about it.

Regards

René

To further Dustin's line of thought (which matches my first line of thinking), is this delay consistent across all the APs' 5GHz radios, or only certain AP(s)? You can use the same "show ap bss-table" to confirm whether the delay correlates to APs operating in DFS channels or not.

Lastly, which AP model(s) are you experiencing the delay with?

When this is happening try running 

show ap remote bss-table <ap-name>

That will query from the AP directly instead of the controller STM process.

Hi Marcus

I will try that, thanks

you can use "show ap active" and check if the  AP in question has a "Q" flag in its flags list. Q being "DFS CAC timer running".

In some regulatory domains the Q flag can remain for up to 15 minutes - which is quite a while especially if the AP is serving a specific area.

you were right. Your Answer correlates to a different answer from the most competent Aruba employee I know (user sadams) that I received in the german airheads. I post it here to give you a complete view:

This sounds like the 5Ghz radio observing mandatory wait times before using a DFS channel ? show ap active has a flag which indicates the radio is in this status: Q = DFS CAC timer running; Channel Availability Check Time: The time a system shall monitor a channel for presence of radar prior to initiating a communications link on that channel Defined by the ETSI EN 301 893 standard, the CAC is 60 seconds, but some frequencies require 10 Minutes. NOTE 1: For channels whose nominal bandwidth falls completely or partly within the band 5 600 MHz to 5 650 MHz, the Channel Availability Check Time shall be 10 minutes. The SSID appears after what seems like 5-6 minutes because the timer has started 4-5 minutes prior to the display time being established. This behavior is common to all Aruba (in fact all 802.11 compliant products) products and versions, the CAC time may change based on the newest ETSI standard. If you observe what appears to be problematic behavior, take a look at the ap tech-support logs (contain driver specific log entries about radio status) and the output of "show ap active" and "show ap bss-table".

nice one, thanks for cross posting - that's a much better answer - inline with the verbosity and detail we know and expect from Shawn

Hi Charlie

Yes, the delay is consistent, if I get that correct.

We use the AP-515 and AP-325.