Bug 87355

              Not really a bug in the system, it is a bug in the FreeBSD
Handbook: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/network-wireless.html

Section 26.3.3.2.2
states that you should

# sysctl net.link.ether.bridge.enable=1
# sysctl net.link.ether.bridge.config="wi0,xl0"
# sysctl net.inet.ip.forwarding=1

On FreeBSD versions earlier than 5.2, you need to use the following
options instead:

# sysctl net.link.ether.bridge=1
# sysctl net.link.ether.bridge_cfg="wi0,xl0"
# sysctl net.inet.ip.forwarding=1


but the line # sysctl net.link.ether.bridge.config="wi0,xl0"

has a comma between wi0 and x10 that should not be there

this little error in the handbook has made me spend about 4-5 hours trying
to debug it.

The manual pages for the wi and ath both have the correct syntax.  Please
fix this so that other users trying to set up a bridge will not run into
this problem... I had absolutely no idea what was wrong - and neither did
the first 3 ppl that tried to help me.

Fix: 

Just change the line in the handbook from
# sysctl net.link.ether.bridge.config="wi0,xl0"
to
# sysctl net.link.ether.bridge.config="wi0 xl0"