strange ethernet messages from other stations

[hiro]

I set up a simple wifi router with a usb wifi stick using hostapd and
dnsmasq and iptables masquerading.

this is the stick that gets used with rt2800usb:
07d1:3c16 D-Link System DWA-125 Wireless N 150 Adapter(rev.A2) [Ralink RT3070]

Most things work fine, but some strange packets get sent to all
stations. On STA1 (my laptop)  I receive the following messages when I
look at tcpdump. STA2 is actually only doing some TCP traffic with
someone else if I listen on the AP's interface, but this is what all
stations seem to get whenever another station like STA2 creates some
traffic:

13:38:48.546200 hostapMAC (oui Unknown) > STA2MAC (oui Unknown) Null
Information, send seq 0, rcv seq 16, Flags [Command], length 72
13:38:48.549741 hostapMAC (oui Unknown) > STA2MAC (oui Unknown) Null
Information, send seq 0, rcv seq 16, Flags [Command], length 352
13:38:48.553400 hostapMAC (oui Unknown) Null > STA2MAC (oui Unknown)
802.1B I Information, send seq 0, rcv seq 16, Flags [Command], length
352
13:38:48.610008 hostapMAC (oui Unknown) Null > STA2MAC (oui Unknown)
802.1B I Information, send seq 0, rcv seq 16, Flags [Command], length
352
13:38:52.908946 hostapMAC (oui Unknown) Null > STA2MAC (oui Unknown)
SNA Information, send seq 0, rcv seq 16, Flags [Command], length 121
13:38:53.051504 hostapMAC (oui Unknown) Null > STA2MAC (oui Unknown)
IP Information, send seq 0, rcv seq 16, Flags [Command], length 76
13:38:53.076772 hostapMAC (oui Unknown) Null > STA2MAC (oui Unknown)
Unknown DSAP 0x08 Information, send seq 0, rcv seq 16, Flags
[Command], length 1494
13:38:53.084375 hostapMAC (oui Unknown) Null > STA2MAC (oui Unknown)
Unknown DSAP 0x08 Information, send seq 0, rcv seq 16, Flags
[Command], length 352
13:38:53.349303 hostapMAC (oui Unknown) Null > STA2MAC (oui Unknown)
Unknown DSAP 0x0a Information, send seq 0, rcv seq 16, Flags
[Command], length 76
13:38:53.350993 hostapMAC (oui Unknown) Null > STA2MAC (oui Unknown)
Unknown DSAP 0x0a Information, send seq 0, rcv seq 16, Flags
[Command], length 123
13:38:53.443855 hostapMAC (oui Unknown) Null > STA2MAC (oui Unknown)
Unknown DSAP 0x0c Information, send seq 0, rcv seq 16, Flags
[Command], length 76
13:38:54.411598 hostapMAC (oui Unknown) Null > STA2MAC (oui Unknown)
ProWay NM Information, send seq 0, rcv seq 16, Flags [Command], length
724

I tried to enable AP isolation (ap_isolate=1), but although this
nicely prevents traffic from one STA to reach an other, I still see
the strange packets.

$ hostapd -v
hostapd v1.0
User space daemon for IEEE 802.11 AP management,
IEEE 802.1X/WPA/WPA2/EAP/RADIUS Authenticator
Copyright (c) 2002-2012, Jouni Malinen <j at w1.fi> and contributors

kernel is 3.0.21

hiro