To make a new bridge do:
ip link add <bridgename> type bridge
This command will show all bridges:
ip link show type bridge
Assign an ip address to the bridge (this will be the IP of the host machine)
ip address add <ip address/prefix length> dev <bridgename> scope global
for example:
ip link add testbr0 type bridge
ip address add 10.3.11.254/24 dev testbr0 scope global
Then, if you want to add a host interface to the bridge, you run:
<code bash> ip link set dev <interface> master <bridgename> </code bash>
similarly, use nomaster
to remove it from the bridge.
https://www.linux-kvm.org/page/Networking
https://help.ubuntu.com/community/KVM/Networking
Excellent resource on all iproute2 tools: