Things I found useful or interesting.
# iptables -I FORWARD -m physdev --physdev-is-bridged -j ACCEPT
# ip6tables -I FORWARD -m physdev --physdev-is-bridged -j ACCEPT
If your sound stops working in linux, you may see errors about being unable to connect to ALSA, or mplayer might say "Audio device got stuck!". If you don't want to reboot, killing pulseaudio will usually do the trick:
$ pulseaudio -k