What is the new feature Broadcast Enhancement on the WAX630

It's about on-the-fly conversion for certain IPv4 over-the-air broadcasts to UDP unicast, like ARP, and other broadcast addresses - it exists on the WAC5x already for a while. 

Cisco has this covered on the Wireless Conroller under Multicast/Broadcast config

HP Aruba offers it, certainly for converting ARP broadcast to unicast

Extreme Networks covers it under Multiast and Broadcast enhancements.

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Broadcast Enhancements

This page is to configure Broadcast Enhancements feature to reduce the broadcast packets going on wireless medium. This feature reduces the throughput impact which will be introduced by huge broadcast traffic. This configuration applies to all the SSID in an AP. It is recommended to enable this feature only when AP has less than 20 clients in 5 GHz and less than 10 clients in 2.4 GHz. This feature will be disabled by default.

Below are some of the limitations in this feature.

If we have more than 20 clients in a SSID, This feature won't do broadcast enhancement for that particular SSID.

Broadcast enhancement is not applicable for WDS and Mesh backhaul VAP. Because all the broadcast packets to the Extender/Repeater AP clients should not be converted to unicast packets on ROOT/Base station AP.

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Indeed, RaghuHR  Netgear should document this feature a little bit better, e.g. list the IP address ranges for specific broadcast purposes, like reserved link local addresses, global scope addresses, limited scope addresses.