802.11a/g SSIDs

[hrios]

Is it true that in a dual-mode environment it is recommended to have different SSID names for your G and A radios?

[smahbub]

Its always better to use Unique SSID names for your G and A radios in a dual mode environment.

[scottmac]

Why? Is it an issues with the IOS interface to both radios, or some security issue?

I use an AP 1231 with a/b/g radios at home (with Cisco a/b/g NICs and others) using EAP-TLS with no issues that I've noticed.

I'm not being argumentative, remain calm, it's just that I can't figure out why it would be an issue and I haven't seen / read / heard anything before that would indicate that it could be an issue.

I'm running IOS ver 12.2(13) JA4.

Thanks!

Scott

[wififofum]

Scott,

I am interested in this as well. Is it possible this influences ADU/CB21AGs radio-association selection algorithm? Scott, do you have any info on how the scan mechanism works with all modes enabled? How do you handle your dual-radio deployments - overlay or complementary cell coverage?

Thanks for any insights.

Bruce

[scottosan]

I beleive it is because if you have 802.11b clients on 802.11g, the ap has to slow all traffic on that radio to 11b.

[scottmac]

The original question was A versus G.

The only reason I can think of would be for access privileges or qos (i.e., forcing a multi-band NIC or device to a specific band for specific service or service level).

I'm still looking around on this one.

FWIW

Scott

[wififofum]

Yes that seems to be the best reason to differentiate SSIDs. When in doubt, diversify. Thanks Scott

[petersage]

Does anyone know which band of a/g will be used by a client if both bands are available with the same SSID. Is it based on signal strength, or is 'a' preferred over 'g'?

Also, once associated to an AP on one band, will a client ever switch to the other band (when using cisco or non-cisco wirless cards), eg if the other band has a better signal?

Thanks

Peter

[jim]

Peter,

Here is a White Paper I found quite useful along those lines.

http://www.cisco.com/warp/public/cc/pd/witc/ao1200ap/prodlit/80211_wp.pdf

HTH

Jim

[petersage]

Great - thanks Jim, that is v useful, exactly what I was after.

I liked the line:

"upcoming dual-band 802.11a/g clients have the intelligence to switch between 5 GHz and 2.4 GHz, taking advantage of 802.11a capacity in areas where it is available and switching to 802.11g (or even 802.11b) when it is not. Client devices will endeavor to maintain data rate over frequency band. For example, a client associated to an 802.11a radio at 54 Mbps will seek out an 802.11g radio supporting 54 Mbps before it “downshifts” from 54 Mbps to a lower data rate on the 802.11a radio."

I wonder if "upcoming" mean that clients dont generally do this yet? :-) One for our Cisco Account SE I think!

Thanks again

Peter

[dixho]

Cisco CB21AG does not have capability to do interband roaming. When CB21AG first comes up, it looks for beacons from 802.11a AP. If there is none, then, it switches to 802.11g band. Finally, it looks for any 802.11b APs.

Interband roaming is pretty tough. It is no easy way to find out the association speed for a particular band at a particular spot. The reason is that there is standard for the AP to broadcast the channel utilization. Thus, a stronger signal receive does not mean higher throughput/speed.