What are the OVS (openvswitch) internal ports used for? Why are they reported as down or UNKNOWN? Why is their MTU at 1500 although jumbo frames are used?

Issue

What are the OVS (Open vSwitch) internal ports used for? Why are they reported as down or UNKNOWN? Why is their MTU at 1500 although jumbo frames are used?

[root@overcloud-controller-0 ~]# ip a | egrep 'ovs|br-' | grep -v eth
6: ovs-system: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN 
7: br-ex: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN 
13: br-int: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN 
14: br-tun: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN