Re: [Madwifi-devel] multicast filter bug?

[Sam L. <sa...@er...>]

>> My Linux box is IPv6 enbabled kernel,
>> But it can't assign IPv6 address because of
>> DAD(Duplicate Address Detection) failure.
>> 
>> DAD uses multicast.
>> I think it caused by receiving mcast packet which sent by itself.
>> 
>> Does anyone use IPv6 on ath? device?
> 
> ath0: duplicate address detected!
> ath0: duplicate address detected!
> ath0: duplicate address detected!

Look for this code in wlan/if_ieee80211subr.c:

#ifdef IFF_SIMPLEX
                        if ((ifp->if_flags & IFF_SIMPLEX) &&
                            IEEE80211_IS_MULTICAST(wh->i_addr1) &&
                            IEEE80211_ADDR_EQ(wh->i_addr3, dev->dev_addr)) {
                                /* 
                                 * In IEEE802.11 network, multicast packet
                                 * sent from me is broadcasted from AP.
                                 * It should be silently discarded for
                                 * SIMPLEX interface.
                                 */
                                DPRINTF(ic, ("%s: discard multicast echo\n",
                                                dev->name));
                                goto out;
                        }
#endif

In BSD systems IFF_SIMPLEX is a flag each network interface sets to
indicate   the interface cannot hear it's own transmissions:

#define IFF_SIMPLEX     0x800           /* can't hear own transmissions */

When I ported the wlan code I could find no equivalent for Linux so I left
the issue unresolved.  It's likely the cause of your problems.  You can
probably just enable the code but it would be better to do "the right
thing" when committing a fix.

	Sam