What is the impact of Airgroup on BCMC Optimization?

Aruba Employee

Customer has deployed Broadcast Multicast Optimization in this network. This article is to explain if that would hinder Airgroup deployment by any means.

 

The BCMC Optimization knob is used for controlled flooding of the outgoing broadcast/ multicast traffic. By default this option is disabled. One must enable this knob for controlled flooding of BCMC traffic, with following exceptions: 

 

  • All DHCP traffic will continue to be allowed
  • ARP request packets will continue to be flooded
  • mDNS multicast packets will be allowed

 
The BCMC knob is applied on a VLAN, and will control the BCMC traffic flooding on all VLAN member ports. 

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The AirGroup feature is enabled by default, and will send out limited required multicast mDNS packets, on need basis, bypassing the BCMC knob as listed above. The regular multicast mDNS traffic received by the mobility controller, gets terminated in the control plane, and is not transmitted out. This is independent of the BCMC knob status.
 
If a customer chooses to disable the AirGroup feature, the outgoing mDNS multicast traffic will meet the following treatment:

 

  • If BCMC knob is disabled, all outgoing mDNS multicast traffic will be allowed
  • If BCMC knob is enabled, all outgoing mDNS multicast traffic will continue to be allowed. 

 
With the BCMC knob enabled and AirGroup feature disabled, if a customer chooses to drop the outgoing mDNS multicast traffic, it has to configure an ACL to block multicast mDNS traffic destined to udp port 5353.

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‎06-27-2014 05:46 AM
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We have BCMC enabled on some virtual-aps for multicast IPTV. We were one of the fiest BCMC users.

 

The VLAN setting is fairly recent. We have recently deployed AirGroup. What is the interaction between Virtual-ap BCMC & AirGroup?

Broadcast-Multicast optimization is a VLAN-specific feature within the Aruba controller which when enabled drops most broadcast or multicast traffic on the VLAN member ports, preventing that traffic from flooding the VLAN and thus conserve bandwidth.

Drop Broadcast and Multicast (or broadcast-filter-all) is a VAP-based feature which when enabled drops broadcast/multicast traffic egressing the VAP into the air.

 

When AirGroup is enabled on a controller, it automatically creates exceptions for mDNS traffic to bypass the above knobs.

 

In the Integrated deployment model, enabling or disabling the above controls on the AirGroup controller has no impact on AirGroup functionality. It is however, recommended that both features be enabled to minimize broadcast/multicast traffic on the user VLAN and in the air.

 

In the overlay model, however, the access controller needs to forward mDNS (i.e., multicast) packets to the overlay controller (using the mDNS redirect ACL). Enabling BC-MC optimization on the access controller will cause it to drop broadcast/multicast packets before any ACL can be applied to them. This will cause AirGroup to break.

 

VAP-based broadcast controls on the access controller can be enabled and will not affect Airgroup services using Integrated deployment model but doing so will prevent the overlay controller from pro-actively learning new Airgroup services on the WLAN. AirGroup services will only be learnt when AirGroup servers send out unsolicited mDNS responses.

 

Thanks,
Anshul Bharthan

 

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