Broadcast multicast optimization

When broadcast multicast traffic is flooded over a user VLAN, the gateways must replicate each broadcast multicast frame and transmit it to each AP with active stations participating in the user VLAN via device designated gateway (DDG) tunnels. One gateway in each cluster is assigned a DDG role for each AP that is tunneling traffic to that cluster. Each gateway is responsible for replicating and forwarding unfiltered broadcast multicast frames to each AP that it assumes the DDG role for. The replication and forwarding of broadcast multicast traffic to DDG tunnels can consume significant CPU/thread resources on the gateways in busy network environments impacting application and user experience. The forwarding of unnecessary broadcast multicast traffic also increases the load on APs as each AP must inspect each received broadcast multicast frame received from the overlay tunnels to make a forwarding or discard decision. If no broadcast multicast optimization is enabled in the WLAN, all received broadcast multicast frames will be forwarded to wireless stations participating in the user VLAN the frames were received at the lowest configured transmit data rate consuming valuable airtime. Broadcast multicast optimization can be enabled per user VLAN and is disabled by default. When enabled, the gateways will prevent unnecessary broadcast and multicast traffic from reaching the APs via DDG tunnels. The gateways will discard all unnecessary broadcast and multicast traffic except DHCP, ARP, VRRP and MDNS/SSDP.

Recommendation

HPE Aruba Networking recommends enabling broadcast multicast optimization for each user VLAN to prevent unnecessary broadcast multicast frames from reaching the APs. The feature should be enabled for each user VLAN unless a specific broadcast multicast application that needs to be forwarded is being filtered. To provide the best possible filtering, this feature should be combined with the WLAN profile recommendations outlined in previous sections.

Configuration

Broadcast multicast optimization is enabled within each user VLAN. In classic Central, broadcast multicast optimization is enabled for a user VLAN within the gateway configuration group or device under Other Options.

In new Central, broadcast multicast optimization is enabled within each VLAN profile under Gateway Specific Parameters

Before and after

The following depicts the CPU/thread utilization on customers 7210 series gateway prior to broadcast multicast optimization being enabled on the user VLANs. Without optimization, the average CPU/thread utilization on the gateway was 54%.

The following depicts the CPU/thread utilization on the same 7210 series gateway after broadcast multicast optimization was enabled on the user VLANs. The average CPU/thread utilization was reduced by 40%.