[root@os004kvm001 ~]# ovs-vsctl add-br br0
ovs-vsctl: cannot create a bridge named br0 because a bridge named br0 already exists
[root@os004kvm001 ~]# ovs-vsctl show
15cf6dda-9fd3-4bfe-803b-dd5813f42afc
    Bridge "br0"
        Port "br0"
            Interface "br0"
                type: internal
    ovs_version: "2.12.0"
[root@os004kvm001 ~]# ip link set br0 up
Cannot find device "br0"
[root@os004kvm001 ~]# ip link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp4s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether bc:5f:f4:78:73:27 brd ff:ff:ff:ff:ff:ff
3: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:be:e2:09 brd ff:ff:ff:ff:ff:ff
4: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc fq_codel master virbr0 state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:be:e2:09 brd ff:ff:ff:ff:ff:ff