"dfs band 3 block" default on Cisco AP's

[amercer00]

Does anyone know why band 3 is blocked by default?

Is it OK to enable it, and are the any advantages or disadvantage to doing so for an indoor network?

Thanks,

Allen

[Metin Ozturk]

Hi,

Did you enable the DFS? If so, It is related with country that you select.

Metin

[amercer00]

Yep.  I enabled all bands for my indoor access points.  I'm in the USA.  That should be OK to do, correct?

[Metin Ozturk]

If you set  "world-mode dot11d country-code US indoor" the DFS band 3 is blocked by default. You can use the command "no dfs band block" to unblock all frequencies for DFS.

[amercer00]

I never set "world-mode dot11d country-code US indoor" on my access points, however band 3 was being blocked.  I did "no dfs band block" and it unblocked it.  Now I'm using all of the bands.  That should be OK to do for indoor access points in the USA, right?

[Metin Ozturk]

Which model are you using?

In US The UNII-1 band is designated for indoor operations (5.15-5.25-GHz), The UNII-2 and UNII-2 (5.25-5.35 GHz and 5.47-5.725 GHz) extended bands are for indoor and outdoor operations, and the UNII-3/ISM (5.725 to 5.825 GHz) band is intended for outdoor bridge products and may be used for indoor WLANs as well.

The DFS band blocks are blow;

1—5.150 to 5.250 GHz

2—5.250 to 5.350 Ghz

3—5.470 to 5.725 GHz

4—5.725 to 5.825 GHz

Now you open all frequencies for DFS. If a client device configured to work only in UNII-1 band and your ap operates other than UNII-1 band like 5.350 GHz, the client will not see your ap and can not connect.

[amercer00]

I am using 1600 and 1700 series access points.  We a using iphones, android devices, and various laptops.  Don't most devices support all 4 bands now?  Should I re-disable band 3?

[Metin Ozturk]

You should better disable the band 3 for indoor usage and use the frequencies that do not need DFS.

If your AP operates at these channels, I hope you dont have any problem with any device.

Frequencies and channels at 20Mhz that do not require DFS.

Channel 36 - Frequency 5180

Channel 40 - Frequency 5200

Channel 44 - Frequency 5220

Channel 48 - Frequency 5240

Channel 149 - Frequency 5745

Channel 153 - Frequency 5765

Channel 157 - Frequency 5785

Channel 161 - Frequency 5805

[amercer00]

Cool, thanks.  So I should do a "dfs band 2 3 block" and that should do it?

Just one more question, why do you block the dfs channels?  Why not just let dfs do it's thing and choose a channel for me?

[Metin Ozturk · Accepted solution]

Yes, it will do.

First of all, it is important which channels your clients support in your network. Many older clients may not support UNII-2 and UNII-2 Extended channels.If the clients do not support a channel it should not connect to your APs.

If your location is close to an area that may contain a weather radar than you can not use some DFS channels (116-132). When your AP detects a radar in the area, it will be forced to move another channel and that channel may already be in use by another AP which causing channel interference. This channel changes will cause your clients disconnect/connect again and it will be problem for some applications like VoIP or sensitive devices that do not tolerate channel hopping.