I've created a bridged network Mac OS X 10.8.5 using ifconfig and TUNTAP for OS X to bridge my wireless connection, en0, with a virtual interface, tap0, which I can use for guest VMs:

    $ sudo sysctl -w net.inet.ip.forwarding=1
    $ sudo sysctl -w net.link.ether.inet.proxyall=1
    $ sudo sysctl -w net.inet.ip.fw.enable=1

    $ sudo ifconfig bridge0 create
    $ sudo ifconfig bridge0 addm en0 addm tap0
    $ sudo ifconfig bridge0 up

    $ ifconfig
    en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        ether 28:cf:xx:xx:xx:xx
        inet6 xxxx::xxxx:xxxx:xxxx:xxxx%en0 prefixlen 64 scopeid 0x4
        inet 192.168.100.64 netmask 0xffffff00 broadcast 192.168.100.1
        media: autoselect
        status: active
    bridge0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        ether ac:de:xx:xx:xx:xx
        Configuration:
            priority 0 hellotime 0 fwddelay 0 maxage 0
            ipfilter disabled flags 0x2
        member: en0 flags=3<LEARNING,DISCOVER>
                 port 4 priority 0 path cost 0
        member: tap0 flags=3<LEARNING,DISCOVER>
                 port 8 priority 0 path cost 0
    tap0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
        ether ca:3d:xx:xx:xx:xx
        open (pid 88244)

However, if I tcpdump -i tap0, I only see broadcast traffic. Shouldn't I see a mirror of everything on en0? (192.168.100.33, the host doing the broadcasting, is another unrelate, noisy server on my LAN.)

(I asked a similar question here and will probably close it.)