2.4 GHz WLC Data Rates - Supported rates less than Mandatory

brettlarkins · ‎07-22-2016

I'm looking at some Cisco WLC configs for a customer and under 2.4GHz settings, 11mb is Mandatory, and 5.5, 6, and 9 are set as Supported. 1 and 2 mbps are disabled. There is no other Mandatory rate set on the band.

Can anyone give me an example of why you would want to do this?

Unless I'm mistaken, all mgmt frames are sent at the lowest Mandatory rate... So then wouldn't supporting data rates below the lowest Mandatory rate lead to connectivity issues?

I've always thought that the lowest data rate you want your clients to use would be the one set to Mandatory (And if you had lots of multicast traffic you would set a second, higher, rate to Mandatory as well).

Anybody else see this, have experience with this, or configure things like this?

Thanks!

George Stefanick · ‎07-22-2016

Soooooo... Ive seen similar in the field. I know some cisco and Aruba guys do like 9 supported 12 mandatory on g/a.

I dont feel comfortable with what you mentioned. On 2.4 GHZ its 1,2,5.5, and 11. The 6 is for 802.11g.

Ive seen 5.5 supported and 11 mandatory. The idea having 1 rate supported under a mandatory rate allows a client to step down to TX or RX. The idea of having 2 mandatory, like 12 and 24 is for multicast traffic. Multcast will trigger at a mandatory rate. If all clients are in 24 PHY the ap will trigger at 24. If one client is in 12 phy, then multicast will trigger at 12. And yes, lowest mandatory is for management frames.

"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
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brettlarkins · ‎07-25-2016

Thank you for the reply, George.

I also do not feel comfortable with the configuration and am leaning toward changing it.

Can a client downshift it's data transmission rate below a Mandatory rate and keep a reliable connection? I assumed that if it lost the management frames from the AP, then it would lose it's connection, or at least have a poor connection since that is where the beacons and CSMA/CA all take place isn't it?

There are still some 802.11b clients, so I will need to keep one of the "b" rates enabled and Mandatory... just not sure if I should leave it as-is or change the Mandatory rate to 5.5 since it is already set to supported. Here is how it's currently setup:

1 Mbps Disabled

2 Mbps Disabled

5.5 Mbps Supported

6 Mbps Supported

9 Mbps Supported

11 Mbps Mandatory

12 Mbps Supported

18 Mbps Supported

24 Mbps Supported

36 Mbps Supported

48 Mbps Supported

54 Mbps Supported

Rasika Nayanajith · ‎07-22-2016

if this environment needs to support 802.11b devices, then only you require to enable 1,2,5.5, 11Mbps.

It is recommended to disable these low data rates (& leave 12Mbps mandatory & rest of higher rates as supported). Here is how I set up it in my production network

HTH

Rasika

brettlarkins · ‎07-25-2016

Thank you for your reply, Rasika. I believe there are still a few 802.11b devices in production so I will need to keep one of the rates enabled. The environment is dense enough to disable 1 & 2 mbps for sure, but I am not sure if it is dense enough to disable 5.5mbps for the "b" clients.

Do you see any reason why a data rate lower than the lowest Mandatory rate should be set to "supported"? That is where my confusion is... below is how the customer has their data rates currently set and it does not make sense to me... seems that clients would lose connection or have poor connection if they downshifted below the lowest Mandatory rate since all mgmt frames are sent at Mandatory rate...???