John- Which memory and CPU are you referencing? And do you mind saying which manufacturer and models/code you are using?
-Lee Badman ________________________________________ From: The EDUCAUSE Wireless Issues Constituent Group Listserv [[email protected]] On Behalf Of John Wheeler, Mr. [[email protected]] Sent: Thursday, May 06, 2010 5:06 PM To: [email protected] Subject: Re: [WIRELESS-LAN] Dual SSIDs Hello, My 2 yen: I don’t know if this was covered, sorry if it is repetition. Some architectures have GRE tunnels for each AP, band (2.4 & 5 GHz), and network (number of SSIDs). This overhead tends to build up fast. If you have 2000+ dual band APs with 2 SSIDs, you will be handling 8000 GRE tunnels. Add an SSID or two across the board and watch your free memory and CPU start to creep into uncomfortable areas. Having said that, we run 4 SSIDs on our network (wpa/wpa2, captive portal, Eduroam, and Guest). One of the networks had to be removed from 5GHz to accommodate the load on that CPU. New Controller hardware will help give us some more breathing room. I would say that the GRE tunnel limitation has affected us more than SSID overhead of answering probes and beacon transmissions. Although, I may not be looking at the SSID overhead problem closely enough. Our campus network is running with over 2200 APs in the downtown core of the city. On any given day I can see 6000-11000 foreign SSIDs. It was only when we double the SSID count under a beginning of semester load that our controllers slammed into the wall. Guess who is no longer on 5GHz ;) Cheers, John Wheeler Wireless Network Specialist Network Infrastructure Team – McGill NCS (514) 398-7388 [email protected] From: The EDUCAUSE Wireless Issues Constituent Group Listserv [mailto:[email protected]] On Behalf Of Greg Williams Sent: Thursday, May 06, 2010 2:40 PM To: [email protected] Subject: Re: [WIRELESS-LAN] Dual SSIDs Hello, My two cents: As people have already pointed out, the limiting factors are the overhead from beacons as well as responses to client probe requests. When you consider that each BSSID will be transmitting beacon frames as well as responding to client probe requests (and each AP will respond simultaneously to these probes typically), and that in a typical deployment you have multiple overlapping AP coverage areas (especially in 2.4GHz with greater penetration, which also has only three non-overlapping channels).... you get the point. The overhead from this traffic can add up very quickly. That being said, depending on 1.) how many APs are overlapping in a given area and 2.) whether or not all of the APs are set on the same channel or not in a given area and 3.) the number of clients in the area, we have found that 4-6 SSIDs is where noticeable performance drop-off begins occurring. Hope that helps. Greg Williams Product Manager 415.203.5630 meraki.com<http://meraki.com/> ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.
