ipv6: Strange packet leaked locally to bpf with fxp.

Hi,

I'm seeing a strange packet in tcpdump when sending ICMP6 echo-requests to
the all nodes multicast address (ff02::1) in both -stable and -current.  This 
packet does not appear to get out over the wire, since a 3rd party host will
not observe this packet when attached to a real hub.  However when capturing 
locally, this packet appears before and after the ICMP6 echo request.

These packets seem to contain the ipv6 packet to be sent but offset incorrectly
and with the wrong data.  The destination MAC address seems to be the start 
of the ipv6 packet.  What are these null I packets?  Are they particular 
to fxp?  

[root_at_nemo root]$ tcpdump -vvvvi fxp3
tcpdump: listening on fxp3
08:05:20.213988 3a:40:fe:80:0:0 > 60:0:0:0:0:10 null I (s=1,r=112,C) len=38
                         81ff fe00 f6bf ff02 0000 0000 0000 0000
                         0000 0000 0001 8000 e7c9 3904 0000 b03e
                         7c3f b843 0300
08:05:20.214004 fe80::2e0:81ff:fe00:f6bf > ff02::1: icmp6: echo request (len 16, hlim 64)
08:05:20.214044 3a:40:fe:80:0:0 > 60:0:0:0:0:10 null I (s=1,r=112,C) len=38
                         81ff fe00 f6bf fe80 0000 0000 0000 02e0
                         81ff fe00 f6bf 8100 6dac 3904 0000 b03e
                         7c3f b843 0300
08:05:21.218031 3a:40:fe:80:0:0 > 60:0:0:0:0:10 null I (s=1,r=112,C) len=38
                         81ff fe00 f6bf ff02 0000 0000 0000 0000
                         0000 0000 0001 8000 1eb9 3904 0001 b13e
                         7c3f 8053 0300
08:05:21.218047 fe80::2e0:81ff:fe00:f6bf > ff02::1: icmp6: echo request (len 16, hlim 64)
08:05:21.218086 3a:40:fe:80:0:0 > 60:0:0:0:0:10 null I (s=1,r=112,C) len=38
                         81ff fe00 f6bf fe80 0000 0000 0000 02e0
                         81ff fe00 f6bf 8100 a49b 3904 0001 b13e
                         7c3f 8053 0300
08:05:22.208128 3a:40:fe:80:0:0 > 60:0:0:0:0:10 null I (s=1,r=112,C) len=38
                         81ff fe00 f6bf ff02 0000 0000 0000 0000
                         0000 0000 0001 8000 cade 3904 0002 b23e
                         7c3f d32c 0300
08:05:22.208143 fe80::2e0:81ff:fe00:f6bf > ff02::1: icmp6: echo request (len 16, hlim 64)
08:05:22.208183 3a:40:fe:80:0:0 > 60:0:0:0:0:10 null I (s=1,r=112,C) len=38
                         81ff fe00 f6bf fe80 0000 0000 0000 02e0
                         81ff fe00 f6bf 8100 50c1 3904 0002 b23e
                         7c3f d32c 0300
^C
9 packets received by filter
0 packets dropped by kernel

Note that ipv6 works fine, it's just that these packets prevent me from 
verifying that my other hardware isn't leaking or misformatting packets.

All the best,

Mark
atkin901 at nospam dot yahoo dot com
(!wired)?(coffee++):(wired);