N+N redunancy

[hanwucisco]

Could any of you please explain or send me a link on what an N+N redunancy is? why is it used on some Controllers' design?

thanks,

Han

[Leo Laohoo]

In addition, certain controllers, such as Cisco Wireless Services Module (WiSM) blades on the Cisco Catalyst® 6500 Series Switches, perform various other functions, including application inspection using the Cisco Network Analysis Module, enhanced security with a full stateful firewall and intrusion detection system, and more. Placing the controller in a centralized location simplifies N+1 or N+N redundancy, depending on the size of the network. This redundancy means that for each wireless controller (N) there is at least one backup controller (+1). The backup controller is not positioned to actively contribute to normal system operation but provides a reliable way to protect the network in case of any failure or downtime on the component being used to manage network access.

This is what you are looking for?

[hanwucisco]

Leo,

What i was trying to understand was a sentence,

" N+N redundancy configuraiton allows logically grouping access points on controllers to miniminze intercontroller roaming events"

So, first, I should understand the concept of N+N, is it like this?

for each of the N devices, there is a backup device.

thanks,

Han

[weterry]

N = Number of Active WLCs

N + 1 would mean that if you have 5 WLCs full of APs, you have 1 backup controller to pick up the load should any 1 of your 5 fail.

N + N would mean that if you have 5 WLCs full of APs, you have 5 backup controllers (N + N = 5 + 5) to pick up the load should all 5 of your active controllers fail.

N + N + 1 would mean that if you had 5 WLCs full of APs, you have 6 backup controller (5 + 5 + 1) so that should all 5 active WLCs fail, you could also lose 1 backup WLC and still work...

With all that said,  with licensing and capacity planning,   you could load 250 APs each on 4 controllers, but have all 4 controllers at 500 License, and that might be considered N + N, because you really have 2 WLCs of 500 and 2 spare (just with the load distributed across all 4 (250 + 250 + 250 + 250).....

[hanwucisco]

Weterry,

thanks, it makes sense. But what these redundancy methods have to do with "minimize the roaming events"?

regards,

Han

[Nicolas Darchis]

Well, the less WLCs you have, the less inter-WLC roaming will happen right ?

So in that regards, the Wism or Wism2 since they support 300 or 500 APs respectively, can be a nice backup solution. By opposition to having 84 2106 to support your 500APs for example :-)