802.11n greenfield in a mixed environment

Unanswered Question
Apr 8th, 2009

we plan to have mixed 802.11n deployment coexistence with a/b/g clients. But we want to have some classrooms or labs to run greenfield only where people request 100Mbps bandwidth to transfer large images. What is the best practice to design some small greenfield areas in the mixed environment? And what is the best way to prevent 802.11a users to associate to our 1140s?



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Overall Rating: 3 (2 ratings)
Robert.N.Barrett_2 Wed, 04/08/2009 - 13:18

I can't speak to the interoperability issues, but it seems logical that you can keep 802.11a (and b/g) users off your 802.11n AP's by simply disabling the speeds they can use. The beacon frames will then not list these speeds as being supported, therefore the clients should not attempt to join.

Do you have, or will you have, 802.11a support in some areas? Is it possible you could support 802.11b/g for your legacy clients, and only enable 802.11n for the 5GHz frequencies (and provide no support at all for 802.11a)?

zhenningx Wed, 04/08/2009 - 13:33

Thank you for the reply. It seems I can't disable all the 802.11a speed(at least one has to be enabled). So I have to leave at least 54Mbps?

In our current wireless network, we support all a/b/g clients and we don't want to change that. I am thinking to add one more WLC for greenfield only. We will only add the new 1142 APs to that WLC and do not support 802.11a on that WLC. Are there any better ways to do this?

jeff.kish Wed, 04/08/2009 - 13:40

Additionally, aren't the data rates a global setting? So even if you could disable all rates 54Mbps and under, you wouldn't be able to use 802.11a anywhere, and you're looking to simply devote certain APs to 802.11n.

I honestly don't know how you might accomplish this. I don't have enough experience with 802.11n. Hopefully someone else here does :D

zhenningx Wed, 04/08/2009 - 15:44

Yes the data rates are global settings. So I am thinking to use a dedicated WLC for greenfield APs. I don't want 802.11a users to associate to those small number of APs using non-broadcast SSIDs. I know it is not ideal. But I cannot get any better ideas. :(

zhenningx Wed, 04/08/2009 - 15:45

still cannot get how AP Group can help... Can you set different radio policies to different AP groups?

zhenningx Thu, 04/09/2009 - 06:38

No. From my knowledge, AP Group cannot solve my issue at all. Can you be more specific how AP Group can help on my issue? Thanks.

runningboy01 Thu, 04/09/2009 - 07:29

What controller version are you running? We are running and I am using AP groups and different WLANS to achieve exactly what you are asking. What I did was create a SSID for N only, call it N_Test for example. Also make sure you have WMM and AES encryption on the new SSID. Then create an AP group with only the APs you want the N clients in, assign the new N_Test SSID to that group.

Doing this should help you achieve what you are trying. Only give your N clients the key or access to the N_Test SSID, which would then keep your A clients off.

zhenningx Thu, 04/09/2009 - 07:45

Thank you for that answer. I am using I know I can push different SSIDs to different groups of APs by using AP Group. But the key thing is how to create a N only SSID. The radio policies available under the SSID are:

a only, a/g only, g only and b/g only.

Can you share how did you create a N only SSID?


runningboy01 Thu, 04/09/2009 - 07:48

You are correct, that you can only choose those radios. However, if you create the SSID and only give it the clients you want (The N clients) the key then only they can connect to it. For example, create a SSID with radio policy all, make it WPA2/AES PSK (key is abcdefghijk) for example. Then only give your N clients the key abcdefghijk for the N_Test SSID. Doing so will keep your A clients off of the newly created SSID. You could also do the same thing using 802.1x. Not sure what you are using, but that is how I would do it.

zhenningx Thu, 04/09/2009 - 08:58

Thanks. That might be the best I can do. Even I tell the clients about this N only SSID, they may come with any kind of laptops and connect with A. Even some a/n cards may have some issues in the driver and end up with A. We have no control over what laptops and NICs they will use. It looks Cisco does not have a effective way to block A users completely out of N only network(like the way we block B users out of G only network). Also I cannot find any documents about greenfield design on CCO...


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