Multicast packets dropped on atheros wireless link

Nate Nielsen nielsen-list at memberwebs.com
Fri Dec 16 15:41:23 PST 2005


Certain multicast packets are not making it through an Atheros based
802.11 wireless link. Other drivers/cards (ie: wi) work fine.

Two boxes sitting next to each other running FreeBSD 6.0. The cards are
set up simply:

ifconfig ath0 inet 172.28.2.18/30 ssid tel2 channel 52 \
	mediaopt adhoc

An OSPF daemon is running on both sides of the wireless link, causing
multicast packets to be sent over the ath0 NICs on both boxes. The
multicast packets link local multicast (ie: not routeable multicast).
Although I'm using OSPF it seems any multicast packets would have the
same behaviour.

Running 'tcpdump -pnti ath0' on the first box (which indicentally is the
BSSID for the adhoc link) shows packet pairs like this:

> IP 172.28.2.18 > 224.0.0.5: OSPFv2, Hello, length: 48
> IP 172.28.2.17 > 224.0.0.5: OSPFv2, Hello, length: 44
> IP 172.28.2.18 > 224.0.0.5: OSPFv2, Hello, length: 48
> IP 172.28.2.17 > 224.0.0.5: OSPFv2, Hello, length: 44

These are packets from both OSPF daemons showing up on the ath0 NIC.
This is the expected behaviour.

However running 'tcpdump -pnti ath0' on the second box we see only:

> IP 172.28.2.17 > 224.0.0.5: OSPFv2, Hello, length: 44
> IP 172.28.2.17 > 224.0.0.5: OSPFv2, Hello, length: 44

The packets from the BSSID box never make it over the wireless link.

FWIW, setting up the two boxes as hostap/client mode doesn't fix the
problem. The multicast packets from the hostap box aren't received on
the client.

Any ideas on where I should poke around?

Cheers,
Nate



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