FreeBSD после 2950,
#tcpdump -i em1
что ето такое ?

11:14:29.906051 01:00:0c:cc:cc:cd (oui Unknown) > 00:12:00:3f:7f:58 (oui Unknown) snap ui/C
        0x0000:  0100 0ccc cccd 0012 003f 7f58 8100 e087  .........?.X....
        0x0010:  0032 aaaa 0300 000c 010b 0000 0000 0080  .2..............
        0x0020:  8700 0c85 a5b0 0000 0000 1380 8700 1200  ................
        0x0030:  3f7f 4080 1801                           ?.@...
11:14:29.907302 01:00:0c:cc:cc:cd (oui Unknown) > 00:12:00:3f:7f:58 (oui Unknown) snap ui/C
        0x0000:  0100 0ccc cccd 0012 003f 7f58 8100 e088  .........?.X....
        0x0010:  0032 aaaa 0300 000c 010b 0000 0000 0080  .2..............
        0x0020:  8800 0c85 a5b0 0000 0000 1380 8800 1200  ................
        0x0030:  3f7f 4080 1801                           ?.@...
11:14:29.908801 01:00:0c:cc:cc:cd (oui Unknown) > 00:12:00:3f:7f:58 (oui Unknown) snap ui/C
        0x0000:  0100 0ccc cccd 0012 003f 7f58 8100 e089  .........?.X....
        0x0010:  0032 aaaa 0300 000c 010b 0000 0000 0080  .2..............
        0x0020:  8900 0c85 a5b0 0000 0000 1380 8900 1200  ................
        0x0030:  3f7f 4080 1801                           ?.@...
11:14:29.910676 01:00:0c:cc:cc:cd (oui Unknown) > 00:12:00:3f:7f:58 (oui Unknown) snap ui/C
        0x0000:  0100 0ccc cccd 0012 003f 7f58 8100 e098  .........?.X....
        0x0010:  0032 aaaa 0300 000c 010b 0000 0000 0080  .2..............
        0x0020:  9800 0c85 a5b0 0000 0000 1380 9800 1200  ................
        0x0030:  3f7f 4080 1801                           ?.@...

• Хелп, 2950 и FreeBSD,s90, 13:27 , 09-Ноя-07

не обращай внимания, просто твой интерфейс воткнут в железку с VLAN, то что ты видишь это работа протокола Per-VLAN Spanning Tree
http://en.wikipedia.org/wiki/Spanning_tree_protocol
http://ru.wikipedia.org/wiki/STP