Bridge interfaces are virtual bridges. When you add an existing interface to a bridge it's just like patching a network port into a physical bridge.
When creating a bridge interface, the new bridge interface becomes the primary interface that you talk to. It assumes control of whatever your original physical interface was doing. This is dangerous if you are bridging your primary ethernet interface because if you don't setup the bridge correctly you will be locked out of your machine.
Using brctl you can add new bridge interfaces and add other interfaces to it.
brctl addbr br0 brctl addif br0 eth0
This replaces eth0 with a bridge interface, br0. You don't need to use brctl to add the bridge or add interfaces to it.
Edit /etc/network/interfaces. Remove any sections like this:
auto eth0 iface eth0 inet static address 10.10.10.37 ...
Replace it with a section like this:
auto br0 iface br0 inet static address 10.10.10.37 netmask 255.255.255.0 gateway 10.10.10.1 bridge_ports eth0 bridge_hello 1 dns-nameservers 10.10.10.2 dns-search example.com
ssh -o Tunnel=ethernet -f -w 0:0 10.10.10.7 true
ifconfig tap0 up brctl addbr br0 brctl stp br0 on ifconfig br0 up brctl addif br0 tap0 ip route add 10.10.10.0/24 dev br0 ip route add default via 10.10.10.1