Broadcast filtering

Each WLAN profile supports the option to filter unnecessary broadcast multicast frames prior to forwarding in addition to converting specific ARP requests destined to wireless stations to unicast. Broadcast filtering applies to all broadcast multicast frames transmitted by AP radios for all forwarding modes. When enabled in a WLAN profile, the AP will filter specific broadcast and multicast frames prior to transmission except the broadcast multicast frames that are permitted by the filtering option.

When no broadcast filtering is applied to a WLAN profile, all broadcast multicast frames propagated over a user VLAN with active wireless stations will be forwarded over the air at the lowest configured transmit data rate. This includes layer 2 and layer broadcast and multicast frames which include spanning-tree bridge protocol data units (BPDUs), virtual router redundancy protocol (VRRP) advertisements, multicast DNS (MDNS) and more. All transmitted broadcast and multicast frames are received by all wireless stations associated with the BSSID regardless of actual assigned VLAN.

Recommendation

WLAN profiles support four broadcast filtering options. HPE Aruba Networking recommends configuring most restrictive filtering option ARP for each WLAN. When the ARP option is selected, the AP filters all broadcast and multicast frames except DHCP, ARP, IGMP and IPv6 neighbor discovery unless DMO is enabled. When DMO is enabled, MDNS and SSDP multicast frames will be forwarded. Additionally, ARP requests destined for wireless stations originating from the LAN or an overlay tunnel are converted to unicast and forwarded to the recipient wireless station as its unicast data rate.

Configuration

Broadcast filtering is enabled within each WLAN profile. In classic Central, broadcast filtering is configured for each WLAN under Broadcast filtering

New Central includes intelligent defaults for each WLAN profile based on the Network Configuration selection. The selected Network Configuration option determines the broadcast filtering option that is applied to each WLAN profile:

• Most Compatible – Disabled
• Balanced – ARP
• High Density – ARP
• Custom – User defined

A custom broadcast filtering option is configured under Broadcast Filtering

Before and after

The following packet capture depicts the broadcast multicast traffic received by a wireless station when no broadcast filtering is applied to the WLAN profile. Note the variety of broadcast multicast frames that are forwarded and received by the wireless stations:

The following packet capture depicts the broadcast and multicast frames received by a wireless station when the recommended broadcast filtering ARP is applied to the WLAN profile. Note that only necessary broadcast multicast frames are forwarded and received by the wireless stations: