How do I optimize multicast traffic?

By Arunkumar posted Jul 02, 2014 09:10 AM


Product and Software: This article applies to all Aruba controllers that run ArubaOS 3.4 or later.


Without any special tuning, multicast packets are sent at either basic rate or support rate, whichever is lower. For example, if you have the following rates:


802.11a Basic Rates 18 24 802.11a Transmit Rates 6 9 12 18 24 36 48 54
Multicast/broadcast packets are sent at 6 Mb/s (when the 5 GHz channel is used) because it is the lowest of all rates. This applies to 'N' as well.


BC/MC Rate Optimization


When this feature is enabled, the control rate is used instead of the lowest of the basic rate and transmit rate. The multicast traffic rate could go up to 24 Mb/s. Note that the multicast traffic is still sent to the multicast MAC address.


For more information on these three rates, refer to KB Answer ID 435.


Dynamic Multicast Optimization


The controller keeps a record of the stations in each multicast group, converts the multicast MAC to unicast MAC (destination IP address remains as multicast), and sends to that station at the unicast rate.


To enable it:


(controller) (Virtual AP profile "default") #dynamic-mcast-optimization?


dynamic-mcast-optimiz.. Enable/Disable dynamic multicast optimization (DMO)
dynamic-mcast-optimiz.. Maximum number of HT STAs in a multicast group
beyond which dynamic multicast optimization stops.
Allowed range [2-255]

(controller) (Virtual AP profile "default") #dynamic-mcast-optimization ?

(controller) (Virtual AP profile "default") #dynamic-mcast-optimization-thresh ?
<dynamic-mcast-optimi.. Maximum number of HT STAs in a multicast group
beyond which dynamic multicast optimization stops.
Allowed range [2-255]


(controller) #show wlan virtual-ap default


Virtual AP profile "default"
Parameter                                 Value
---------                                 -----
Virtual AP enable                         Enabled
Allowed band                              all
AAA Profile                               default
802.11K Profile                           default
SSID Profile                              default
VLAN                                      N/A
Forward mode                              tunnel
Deny time range                           N/A
Mobile IP                                 Enabled
HA Discovery on-association               Disabled
DoS Prevention                            Disabled
Station Blacklisting                      Enabled
Blacklist Time                            3600 sec
Dynamic Multicast Optimization (DMO)      Disabled <<<<<<<<<
Dynamic Multicast Optimization (DMO)      Threshold 6 <<<<<<<<<
Authentication Failure Blacklist Time     3600 sec
Multi Association                         Disabled
Strict Compliance                         Disabled
VLAN Mobility                             Disabled
Remote-AP Operation                       standard
Drop Broadcast and Multicast              Disabled
Convert Broadcast ARP requests to unicast Disabled
Band Steering                             Disabled
WMM Traffic Management Profile            N/A


Works on all APs (legacy or 11n), however, only works on newer platform (M3 or 3000 series controllers).


· Needs to enable IGMP proxy.


· IGMP query always optimized and send to each station by the controller.


· DMO threshold is per virtual AP profile and per AP, not per radio. For example, consider a dual-radio AP that has the DMO threshold configured as 6 and there are six users on the 5 GHz band. When the seventh user joins, regardless of the RF band, the DMO falls back to the traditional behavior. No multicast to unicast conversion occurs. Multicast is sent as multicast into the air.


This is important if VLAN pooling is configured. In that case, a higher DMO threshold is desired. The number depends on the combination of several factors such as the size of the VLAN pool, the number of receivers, and the density of the receivers.




When you optimize multicast traffic, DO NOT enable "broadcast-filter all" in the virtual AP profile. This feature is designed to reduce excessive multicast and broadcast traffic when the customer has a flat LAN (for example, a /16 IP subnet). When this feature is enabled, the controller drops all broadcast and multicast traffic except for DHCP.


For more details on "broadcast-filter" usage.