John,
Others on the list have responded and given some good answers to your question.
Let me add my experience and 2 cents.
At Emory we have 1500 APs running in two Aruba systems - one for the Academic
side of the house and one for our Healthcare organization. Needless to say,
our Healthcare organization demands high availability :-)
Our architecture is similar on each side - one set of redundant master
controllers and multiple local controllers. In the Aruba architecture, the
masters' function is to manage overall global issues - configuration, user and
AP lists, heat maps, IDS correlation functions, etc. Masters can also support
AP connections, like the local controllers.
We don't have any APs homing to our master controllers (but we could if we
wanted to). Instead, we home APs to local controllers. We also have a
dedicated local controller as a "back-up", i.e., if any of the local
controllers fail, the APs would re-home to the backup. We have one local
backup/system, and can withstand ONE controller failure at a time. Initially
this a bit pricy, but as we've expanded, we find that a single backup
controller works very well. In the past two years, we've only lost one
controller (bad sup card), so our backup controllers are idle virtually all of
the time.
BTW - it is EASY (and necessary) to direct an AP or group of APs to specific
controllers. In the command line, the syntax (vers 2.5 and below) is "ap
location <location code> lms-ip <specific controller IP address>". You can
also set the backup controller using (again, ver 2.5 and below) "ap location
<location code> bkplms-ip <backup controller IP address>".
There are a number of ways to build redundancy with the Aruba system, with the
best way dependent on your situation.
The method you mentioned with interleaving APs to different controllers WILL
work because of Aruba's mobility/roaming capability. The problem arises if you
only have one master and one local. Losing the master will prevent the global
functions from happening (heat map, configuration, IDS correlation, etc) and
the loss of "servicing" APs that are homed to it. Losing the local results in
loss of ability to service the APs homed to it.
Aruba licenses each controller to support a set number of APs. If you lose a
controller, those APs will home where you told them to go, but if that backup
doesn't have capacity (based on it's licensing) to handle those APs, they are
effectively down. That's why we use an N+1 local controller model for our
redundancy - a dedicated backup can handle all APs on any active controller -
but sits idle most of the time.
I realize that my ramblings on this subject may not be quite clear - so if you
need additional explanations, or just want to pick my brain, touch base with me
off the list. I've gone over a number of different redundancy scenarios as
we've built our network, and may be able to offer some useful advice.
>>-> Stan Brooks - CWNA/CWSP
Emory University
Network Communications Division
404.727.0226
[EMAIL PROTECTED]
AIM: WLANstan Yahoo!: WLANstan MSN: [EMAIL PROTECTED]
-----Original Message-----
From: John Rodkey [mailto:[EMAIL PROTECTED]
Sent: Tuesday, May 22, 2007 7:24 PM
To: [email protected]
Subject: [WIRELESS-LAN] 'Clustering' and 'failover' in the context of Aruba
We are currently considering expanding our existing wireless environment to
cover additional dorms.
By doing so, we will exceed the capacity of our current controller, and can
either add an additional controller card or for a slight incremental cost, add
another controller. We planned to add the additional controller, with the idea
that the controller would allow redundancy/failover/clustering to happen, so
that if one controller were to go down, for instance, the other would take over.
We were subsequently told that this was a faulty understanding of the failover
function.
So we thought we might be able to try another approach: every other WAP would
be controlled by alternating controllers.
That way, if controller A, with waps 1,3,5,7,9... on it were to go down, the
coverage in any given building would be halved, because controller B, with waps
2,4,6,8 ... would continue to run.
Nope, that is a bad idea, says the contact: each controller will maintain its
own heat map and routing info, etc. and as a result, there would be nowhere to
look for a unified picture of the wireless network.
So I'm confused: what is the exact nature of controller clustering or failover
under Aruba?
Given somewhere in the neighborhood of 200 APs, how should one configure the
controllers
John
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