How does AP load balancing work on Aruba APs in ArubaOS 3.3.1?

Aruba Employee

Product and Software: This article applies to all Aruba controllers and ArubaOS OS 3.3.1.

 

Use Case/Application

AP load balancing is a feature that allows the administrator to distribute wireless users between Access Points (APs) in the same area. This feature is used mainly in conference rooms and during events when you have large number of users near one AP, and you have other APs in the same area covering the same location on different channels and with different signal RSSIs.

 

Using this feature, the administrator can avoid having one AP congested, while other APs in the same area are idle or under-utilized.

 

To use AP load balancing, you should:

  •     Have more than one AP covering the same area (ARM will take care of course of having them in different non-overlapping channels).
  •     Disable local-probe response for APs where load balancing is needed. This is to make sure probe requests are processed at the controller.

To disable local-probe response, follow these steps:

 

From GUI:

 

Configuration > AP Configuratoin > <AP Group Name> > Wireless LAN > Virtual AP > SSID Profile > Advanced tab

 

or

 

Configuration > Advanced Services > All Profiles > Wireless LAN > SSID Profile > <SSID Profile name> > Advanced tab

 

load_balance_KB2.gif

 

From CLI:

 

 

configure terminal

 

wlan ssid-profile "loadbalance" 

no local-probe-response

 

The users' wireless card driver should be able to roam to another AP if it fails to connect to the nearest AP. Some old drivers stay with the same high RSSI AP, even if it fails to connect to it many times. Make sure to update your wireless card driver regularly to have the latest features and bug fixes.

 

Parameters to Decide Before Configuring Load Balancing

 

The four major settings in load balancing are:

  •      Low watermark: this can be set for number of users and network utilization.
  •      High watermark: this can be set for number of users and network utilization.
  •      Max Association Retries: this is the number of probes the AP will ignore from the same user to force him to try another BSSID/AP on the same SSID. If the user's driver keeps probing the same BSSID/AP, the AP will respond to him after "Max Retries" of probes. This action is needed to avoid disconnecting users with old or bad drivers. Setting this number very high might disconnect this type of wireless user.
  •      Wait time: time in seconds to wait before enabling or disabling load balancing when the threshold is hit.

High water mark is the threshold that will enable the load balancing state on the AP. In this state, the AP stops responding to probe requests from wireless users. Normal drivers will try another BSSID (another AP), so the number of users is guaranteed not to exceed the high water mark on the AP.

 

When users begin to leave the AP, this AP will stay in the "load balancing" state until the number of user falls below the low water mark. When this happens, the AP leaves the load balancing state and starts responding to probe requests from wireless clients (normal mode).

 

Note that these parameters are per AP-Group in ArubaOS 3.x.

 

The following diagram shows how this feature works in conjunction with the number of users, high water mark (HWM) and low water mark (LWM).

 

load_balance.jpg

 

To configure load balancing in ArubaOS 3.3.1, follow these steps:

 

From GUI:

 

Configuration > AP Configuration > <AP Group Name> > RF Management > RF Optimization Profile

or

Configuration > Advanced Services > All Profiles > RF Management > RF Optimization Profile > <Profile name>

 

load_balance_KB.gif

 

 

From CLI:

 

rf optimization-profile "loadbalance" 
ap-load-balancing 
ap-lb-user-high-wm 20 
ap-lb-user-low-wm 15 
ap-lb-util-high-wm 90 
ap-lb-util-low-wm 80

 

 

Best Practices

 

Keep all values on the default, and change only the following parameters:

 

  •      Enable load balancing if you need this feature.
  •      Change user count low water mark and high water mark based on your requirement and required bandwidth per user. Values of 15 to 25 for high and low water marks are usually used.
  •      Keep a difference of 3 to 5 between user count high and low water marks.

 

How to Monitor Load Balancing

 

When the threshold reached (number of users or utilization on the radio), the following log message is generated:

 

# show log wireless x

 

Jun 1 13:12:40 :404041: <WARN> |AP TEST@192.168.0.234 sapd| AM 00:0b:86:31:8e:a0: Enabling Load Balancing on AP 00:0b:86:31:8e:a1 NU <high-water-mark or higher> (if it is number of users based)

Jun 1 13:12:40 :404041: <WARN> |AP TEST@192.168.0.234 sapd| AM 00:0b:86:31:8e:a0: Enabling Load Balancing on AP 00:0b:86:31:8e:a1 BWR <high-water-mark or higher> (if it is utilization based)

 

If you then issue the "show ap monitor ap-list" command, you will see that load balancing is enabled for all APs that reached the HWM and is disabled for all others.

 

 

(Riyadh_Office) #show ap monitor ap-list ap-name RAP2

 

Monitored AP Table
------------------
bssid essid chan ap-type phy-type dos mt it load-balance nstas avg-rssi curr-rssi wired-macs
----- ----- ---- ------- -------- --- -- -- ------------ ----- -------- --------- ----------
00:0b:86:31:8e:a1 test 6 valid 80211b/g disable 1527 0 enable 2 15 15 3

 

- After load balancing is enabled for the AP (SSID), you will keep receiving the following log messages if you debug stm.

 

Jun 1 13:34:19 :501089: <NOTI> |stm| Probe request: 00:19:7d:1e:8a:b7: Dropped AP 192.168.0.234-00:0b:86:31:8e:a1-TEST for Load Balancing SSID test
Jun 1 13:34:19 :501109: <NOTI> |stm| Auth request: 00:19:7d:1e:8a:b7: AP 192.168.0.234-00:0b:86:31:8e:a1-RAP2 auth_alg 0
Jun 1 13:34:19 :501094: <NOTI> |stm| Auth failure: 00:19:7d:1e:8a:b7: AP 192.168.0.234-00:0b:86:31:8e:a1-TEST Reason AP is resource constrained

 

Also, issuing the "show stm packets" command shows an "assoc-resp" with a resource constrained error code.

 

After the low water mark is reached, the following log message is generated.

 

# show log wireless all

 

Jun 1 13:38:09 :404039: <WARN> |AP TEST@192.168.0.234 sapd| AM 00:0b:86:31:8e:a0: Disabling Load Balancing on AP 00:0b:86:31:8e:a1 BWR X NU <low-water-mark or less> (if it is number of users based)

 

Jun 1 13:38:09 :404039: <WARN> |AP TEST@192.168.0.234 sapd| AM 00:0b:86:31:8e:a0: Disabling Load Balancing on AP 00:0b:86:31:8e:a1 BWR <low-water-mark or less> NU Y (if it is utilization based)

 

 

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Last update:
‎07-10-2014 10:38 AM
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