Could it be promiscuous mode?
[root@nas] ~# ifconfig
em0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 1500
options=42098<VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,WOL_MAGIC,VLAN_HWTSO>
ether 68:05:ca:24:f8:35
inet 192.168.0.3 netmask 0xffffff00 broadcast 192.168.0.255
nd6 options=9<PERFORMNUD,IFDISABLED>
media: Ethernet autoselect (1000baseT <full-duplex>)
status: active
em1: flags=8c02<BROADCAST,OACTIVE,SIMPLEX,MULTICAST> metric 0 mtu 1500
options=4019b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,TSO4,VLAN_HWTSO>
ether 0c:c4:7a:03:f3:79
nd6 options=9<PERFORMNUD,IFDISABLED>
media: Ethernet autoselect
status: no carrier
igb0: flags=8c02<BROADCAST,OACTIVE,SIMPLEX,MULTICAST> metric 0 mtu 1500
options=403bb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,TSO4,TSO6,VLAN_HWTSO>
ether 0c:c4:7a:03:f3:78
nd6 options=9<PERFORMNUD,IFDISABLED>
media: Ethernet autoselect
status: no carrier
ipfw0: flags=8801<UP,SIMPLEX,MULTICAST> metric 0 mtu 65536
nd6 options=9<PERFORMNUD,IFDISABLED>
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
options=600003<RXCSUM,TXCSUM,RXCSUM_IPV6,TXCSUM_IPV6>
inet6 ::1 prefixlen 128
inet6 fe80::1%lo0 prefixlen 64 scopeid 0x7
inet 127.0.0.1 netmask 0xff000000
nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
bridge0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
ether 02:fe:4a:c8:9c:00
nd6 options=1<PERFORMNUD>
id 00:00:00:00:00:00 priority 32768 hellotime 2 fwddelay 15
maxage 20 holdcnt 6 proto rstp maxaddr 2000 timeout 1200
root id 00:00:00:00:00:00 priority 32768 ifcost 0 port 0
member: epair2a flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
ifmaxaddr 0 port 11 priority 128 path cost 2000
member: epair1a flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
ifmaxaddr 0 port 10 priority 128 path cost 2000
member: epair0a flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
ifmaxaddr 0 port 9 priority 128 path cost 2000
member: em0 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
ifmaxaddr 0 port 1 priority 128 path cost 20000
epair0a: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 1500
options=8<VLAN_MTU>
ether 02:21:1a:00:09:0a
nd6 options=1<PERFORMNUD>
media: Ethernet 10Gbase-T (10Gbase-T <full-duplex>)
status: active
epair1a: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 1500
options=8<VLAN_MTU>
ether 02:c4:73:00:0a:0a
nd6 options=1<PERFORMNUD>
media: Ethernet 10Gbase-T (10Gbase-T <full-duplex>)
status: active
epair2a: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 1500
options=8<VLAN_MTU>
ether 02:c0:73:00:0b:0a
nd6 options=1<PERFORMNUD>
media: Ethernet 10Gbase-T (10Gbase-T <full-duplex>)
status: active