Roaming and 2.4 vs 5.0 on 1250 series AP design help

Answered Question
Nov 2nd, 2010

Hello,

I will be upfront and honest and state that although I am familiar with some wireless technologies, most of this stuff is a mystery to me. I have done some homework and have researched quite a bit, but have ind of hit a wall.

I have been handed four Aironet 1250 series AP's all with the dual radio modules (2.4 and 5.0). I really need to use only one of the modules so that we can power it via POE and not enchanced POE (long story).

So, I need help with a design. Here's what I'd like to see.

1.       I would like to setup "roaming" so that when a wireless client goes from one AP to another it is seamless to the user and the users NIC will associate with the strongest AP signal. Can I do this by simply setting the same SSID and security on each AP, or must I have a controller to do this?

2.       Also, I cannot seem to get older legacy clients to communicate with the 5.0 Ghz radio module (they can’t even see it) but they work fine when I switch it out for the 2.4. I know this is a very noob question, but can the older clients (non N) work on the 5.0 module)

I have looked through a ton of documentation but there doesn’t seem to be a configuration guide that I can find for what I need to do.

That’s it. Can someone please have mercy on me and point me in the right direction? I will be looking in the mean time but I have a lot of unknowns. I think if I can get the two questions answered above, then I can mark as resolved and run with it.

Thanks a bushel,

dt

I have this problem too.
0 votes
Correct Answer by Nicolas Darchis about 3 years 5 months ago

Hi Dave,

1. Yes, the conditions for a proper roaming are : same SSID, same security settings, and the APs serving the same client subnet (so that client doesn't have to change its ip address).

This is sufficient for data, Fast roaming is required for applications like voice and you can then look into using cckm as key mechanism and configure one AP to act as WDS to centralize the roaming keys.

2. This is not related. 11n is available on both 2.4 and 5 ghz band. The question is if your old adapters are capable of 802.11a or not. 11a is the 54Mbps speed in the 5ghz band. I would guess they are not capable of it.

Adapters that are on laptop now are often "abgn" meaning they can do N speeds on both 2.4 and 5ghz band. An adapter that would be "bg" or "bgn" would typically be restricted to only 2.4 Ghz.

Hope this helps,

Nicolas

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Correct Answer
Nicolas Darchis Thu, 11/04/2010 - 02:07

Hi Dave,

1. Yes, the conditions for a proper roaming are : same SSID, same security settings, and the APs serving the same client subnet (so that client doesn't have to change its ip address).

This is sufficient for data, Fast roaming is required for applications like voice and you can then look into using cckm as key mechanism and configure one AP to act as WDS to centralize the roaming keys.

2. This is not related. 11n is available on both 2.4 and 5 ghz band. The question is if your old adapters are capable of 802.11a or not. 11a is the 54Mbps speed in the 5ghz band. I would guess they are not capable of it.

Adapters that are on laptop now are often "abgn" meaning they can do N speeds on both 2.4 and 5ghz band. An adapter that would be "bg" or "bgn" would typically be restricted to only 2.4 Ghz.

Hope this helps,

Nicolas

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dwtuggle8309 Thu, 11/04/2010 - 17:41

That is some great information......

I had posted another message asking baout supporting legacy clients but after reading your post, I think I understand the problem and what is required of the data rates. This Cisco world of wireless has been a bit more of a challenge than I thought it'd be. It's nice to know that there are folks out there willing to help a noob like me out.

dt

Leo Laohoo Thu, 11/04/2010 - 18:00

An adapter that would be "bg" or "bgn" would typically be restricted to only 2.4 Ghz.

Interesting.  Mighty interesting.  Cisco was asked to design a study for implementation of WiFi in a public hospital and one of the things they've recommended is disable 802.11b.

I know for a fact that some poorly written wireless codes make some wireless bio-medical equipment talk only in 802.11b and in Australia, alot of laptops/netbooks only have b/g/n radios.  (I have no idea as to the reason why 802.11a is not included.)

I'll be meeting a Cisco WiFi guru from Singapore next week and I'll raise this topic up with him.

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Posted November 2, 2010 at 7:09 PM
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