(KAME-snap 9225) Re: DUPlicate icmpv6 echo replies over wi0

[Sam Leffler]

Greg Troxel wrote:
> The 802.11 mac layer can cause duplicates.  If the receiver hears the
> packet and sends an ack, but the ack is lost, the sender will
> retransmit, leading to two copies of the packet.  In theory a receiver
> could filter dups, but I haven't noticed code to do this.  So I would
> suggest trying with other traffic and seeing if it is really a
> ICMPv6-specific problem.  Your description makes it sound to me like
> something other than 802.11 MAC-layer dups are happening, though.  I
> would also suggest tcpdumping on the host behind the router and the
> hostap machine.
> 

802.11 detects dups at the link layer; there's a sequence number.  For 
wi you wouldn't see code as this is done in the firmware (except 
possibly for hostap operation which isn't going on here).

The best way to isolate out what's going on is to sniff from a 3rd station.

	Sam