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charset="utf-8" Content-Transfer-Encoding: quoted-printable Hi Julian, Johannes, Thank you both for the great discussion and perspectives! Putting the two points together gives a very clear and coherent picture: 1. Julian correctly pointed out the real security risk with Hole-196: Attackers can abuse not only unicast ARP replies, but also broadcast GAR= P announcements (sip =3D=3D tip =3D=3D gateway_ip) to poison peer caches i= n a shared-key network. 2. At the same time, as Johannes reminded, Linux already has a dedicated kn= ob for that specific broadcast behavior: `drop_gratuitous_arp`. Looking at the existing architecture, the two knobs complement each other naturally: - `drop_unicast_in_l2_multicast`: strictly enforces the L3/L2 boundary by dropping unicast IP and unicast ARP replies (sip !=3D tip) inside L2 BMC. - `drop_gratuitous_arp`: drops broadcast GARP (sip =3D=3D tip) without tang= ling broadcast filtering logic into the unicast knob. This means users defending against Hole-196 can achieve complete coverage by enabling both knobs on the wireless interface, without needing to overlo= ad `drop_unicast_in_l2_multicast` or change core neighbor learning behavior. This also means [PATCH net v5] (which dropped IP changes and strictly filte= red non-GARP replies) is architecturally aligned. We can document this dual-kno= b recommendation in ip-sysctl.rst so administrators know how to fully secure shared wireless links. Julian, Johannes =E2=80=94 what do you think about this unified direction? Best regards, Star Chang