MT7621 arp broadcast issue

Symptoms:

• all WiFi clients has internet access
• after some time, cannot reach WiFi client from another client (WiFi or Wired)

Affected routers:

• My devices: Netgear R6220 MediaTek MT7621 ver:1 eco:3
• D-Link DIR-882 (MediaTek MT7621A SoC)
• Cudy WR2100, MT7621 chipset, MT7603E Wifi.

Problem introduced by Kernel: [PATCH v2] net: dsa: tag_mtk: add padding for tx packets

OpenWrt issue:

• ARP/broadcast issues for wireless clients on Mediatek-based routers using OpenWrt as dumb AP in pfSense/OPNsense bridged LAN firewall setups on 22.03.3 release, present since OpenWrt 22.03.0-rc2 #11942
• Device stops passing broadcast packets to wireless interfaces after 24H of uptime
• Other chipsets - similar problem: ARP requests are not forwarded to Wifi Client after some time --> devices unreachable #9555
• Maybe related Clients in same WLAN can’t reach each other

• broadcasts delivery problem #598

Reported as fixed in:

• r22186-9307c2753980
• >= v22.03.4

Problem still occurs in:

• OpenWrt 23.05-SNAPSHOT r24041-a07a531329

Potential fix:

• Re: Potential Broadcast Issues After GTK Key Exchange on ath11k with IPQ8072A (QCN5024/QCN5054)
• https://github.com/openwrt/openwrt/issues/9555#issuecomment-2563690019

Workaround:

• execute command `wifi` on remote OpenWrt