Cisco Load Balancing Feature

In this post we will learn about Load Balancing feature on WLC.

Normally this feature is called as Aggressive Load Balancing. This feature mainly does the Wireless clients load-balance across APs.

As per my opinion, it’s a very cool feature be able to balance client distribution on the wireless network.

Must Remembering Points:

***Note: Clients are load balanced between access points on the same controller. Load balancing does not occur between access points on different controllers.

***Note: It works at the association phase.

How it works:

When a Client tries to associate to a LAP, association response packets are sent to the client with an 802.11 response packet including status code 17. The code 17 indicates that the AP is busy (Means no more can associate to me, so please find other AP) .

The AP responds with an association response bearing ‘success’ if the AP threshold is not met, and with code 17 (AP busy) if the AP utilization threshold is reached or exceeded and another less busy AP heard the client request.

Now here arises a problem: If AP discarded or sends a status code 17 to Client then client have to decide to ignore it or still use the same AP. Some of client driver uses the same AP for connection once again but most of the other type of clients tries to find other AP for connection. (So this process depends on vendor drivers, you cannot force them to use specific AP).

Globally configuration:

Via GUI:

Wireless > Advanced > Load Balancing

Load-Balance1

 Via CLI:

(WLAN1) >config load-balancing ?
 denial         Configures Aggressive Load Balancing denial count.
 window         Configures Aggressive Load Balancing client window.
(WLAN1) >config load-balancing window ?
 <client count> Number of denials <0 to 20>.
(WLAN1) >config load-balancing denial ?
 <denial count> Number of denials <1-10>.
(WLAN1) >config load-balancing denial 3

Client Window Size:  The client size window and client on least loaded AP determine the load-balance threshold value.

Before configure the load balancing intelligence, remember the formula. An AP is considered busy once it has a number of associated clients equal to the Client Window Size plus the number of clients on the least loaded AP in the area.

Load-balancing threshold = Client window size + number of clients on the least loaded AP

Example: Suppose I have 3 AP.

AP1: 9 Clients
AP2: 7 Clients
AP3: 4 Clients

As per last screenshot I have Client Window Size is 5.

As per the formula, Load balance Threshold is = 5+4 = 9

Means if any new client wants to Join AP1 then client will get the status 17 (Busy) message or in other words this AP (AP1) considered to be busy.

The Maximum Denial Count parameter allows the user to configure the number of times the client associations will be rejected for a particular AP. The Maximum Denial Count can have a value between 0 and 10.

Configuration Per WLAN Basis:

Via GUI:

WLAN > Advanced > Client Load Balancing

Load-Balance2

Via CLI:

(WLAN1) >config wlan load-balance ?
 allow          Allow|Disallow Load Balance on a WLAN.
 (WLAN1) >config wlan load-balance allow  ?
 enable         Allow Load Balance on a WLAN.
 disable        Disallow Load Balance on a WLAN.
(WLAN1) >config wlan load-balance allow  enable 8
 WARNING: Allowing load balance on this WLAN may impact time sensitive application like VOICE. Continue? (y/N)y
(WLAN1) >

Verification:

(WLAN1) >show load-balancing
 Aggressive Load Balancing........................ per WLAN enabling
 Aggressive Load Balancing Window................. 5 clients
 Aggressive Load Balancing Denial Count........... 3
 Statistics
 Total Denied Count............................... 0 clients
 Total Denial Sent................................ 0 messages
 Exceeded Denial Max Limit Count.................. 0 times
 None 5G Candidate Count.......................... 0 times
 None 2.4G Candidate Count........................ 0 times
(WLAN1) >show wlan 8
 WLAN Identifier.................................. 8
 Profile Name..................................... Test
 Network Name (SSID).............................. Test
 .
 .
 Band Select...................................... Enabled
 Load Balancing................................... Enabled
(WLAN1) >

That’s all about this feature 🙂

Advertisements

7 Comments

  1. Hi!!,
    good explanation! but I have a doubt, if i have 3ap´s in a conference room and monitoring i have:

    ap1: 70 clients
    ap2: 8 clients
    ap3: 5 clients

    How can i do to put a great part of clients from ap1 to ap2 or ap3?? turn down tx power for ap1? all ap´s inthe same level of tx power?

    what is on the least loaded ap for ap1…..i have 70 clients???
    how do i put the load balance trheshold to 40 clients in ap1?
    i enable windows size to 5
    denial count to 8?
    check in client load balancig?

    Thanks for your help!

    Golbert

  2. Hi!!,
    good explanation but i have a doubt, if i have 3 ap´s in a conference room: when i am monitoring i see:

    ap1: 70 clients
    ap2: 15 clients
    ap3: 8 clientes

    how can i do in order to put great part of de clients from ap1 towards ap2 or ap3???

    maybe put in the same level the tx power all aps??
    enable windows size to 5?
    denial count to 8 maybe??
    check for client load balancing?

    how i can determinate the load balance threshold for that figure??…i would like to put ap1 only for 40 clients and the rest can go to ap2 or ap3…is this possible?
    in what moment ap1 will get status 17???

    thanks for your help!!!

    Golbert

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s