broadcast packets are being lost

michael-dev michael-dev at fami-braun.de
Mon Mar 10 09:18:15 EDT 2014


Hi,

I've been debugging a very similar issue the last few days.
Although I did not find a bug in hostapd, there are some hostapd 
settings that helped me getting much more of the broadcast/multicast 
packets through.

The required hostapd setting is "dtim_period=1" (related to a 
combination of sta and ap issues), and "beacon_int=400" helped too 
(related to ath9k on AP-side).

Alternatively you can try to disable wireless powersaving on *all* 
stations.
That is running
  iw dev wlan0 set power_save off
on all stas.
When there is no sta in power_save mode, the multicast packets won't get 
buffered for bulk delivery at dtim period.

Regards,
  M. Braun

Am 05.03.2014 21:37, schrieb Khaled:
> Hello
> 
> I'm new to hostap and this mailing list, so please redirect me if I'm
> not asking in the right place.
> 
> I'm trying to use a RaspberryPi with a WIFI dongle (containing an
> RTL-8188 chip, I believe) as a WIFI router.
> 
> 
> 
> I'm using this for hostapd.conf:
> 
> #############################################
> ctrl_interface=/var/run/hostapd
> ctrl_interface_group=wheel
> 
> # Some usable default settings...
> macaddr_acl=0
> auth_algs=1
> ignore_broadcast_ssid=0
> 
> # Most modern wireless drivers in the kernel need driver=nl80211
> driver=nl80211
> 
> # Customize these for your local configuration...
> interface=wlan0
> hw_mode=g
> channel=6
> ssid=FuzzWifi4
> wpa=2
> wpa_passphrase=mypassword
> ################################################
> 
> 
> 
> This configuration is mostly working well. All my devices can connect,
> IPs are assigned via DHCP, and regular (unicast) traffic is flowing
> nicely. I've also found it to be reliable, downloading for days
> continuously without issues.
> 
> *However*: I'm noticing strange behaviour with regards to broadcasts.
> When sending broadcast packets from any connected WIFI device, those
> packets are reliably received by the RaspberryPi (the access point)
> itself. However, all other clients on the same WIFI only see about 5%
> of those packets.
> 
> For example, if host (a) and (b) are connected via WIFI and host (a)
> starts broadcasting (for example, with ping -b), the RPi will see 100%
> of those pings, but host (b) will only see the occasional ping (about
> 5% only). Same is true for the reverse: when b is broadcasting, (a)
> doesn't see most broadcasts, but the RPi sees all of them. I'm
> confirming this using tcpdump on all three devices.
> 
> No other issues are observed: clients can send unicast traffic without
> any issues.
> 
> Any ideas what could be the problem here? Any help is appreciated.
> 
> Thanks
> -Khaled
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