If you check the ‘ifconfig -a’ after a fresh install of RHEL/CentOS 6,7 system, you would find the interfaces virbr0 name. Here is an example from freshly installed CentOS 7 system.
# ifconfig -a
....
virbr0: flags=4099[UP,BROADCAST,MULTICAST] mtu 1500
inet 192.168.122.1 netmask 255.255.255.0 broadcast 192.168.122.255
ether 52:54:00:d5:f2:0c txqueuelen 1000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
virbr0-nic: flags=4098[BROADCAST,MULTICAST] mtu 1500
ether 52:54:00:d5:f2:0c txqueuelen 1000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
What is virbr0 interface
The virbr0 bridge interface is created by libvirtd’s default network configuration. libvirtd is the service which provides a basis for the host to act as a hypervisor. So in case you are not using xen virtualization, you can either prevent libvirtd’s default network from being activated on boot, or you could prevent libvirtd itself from activating on boot. The former will prevent any VM guest attached to libvirtd’s default network from having network connectivity and the latter would prevent VMs from running at all. Which is fine if you are not using it.
Disable libvirtd default network
1. You can disable libvirtd’s default network temporarily using the virsh command. This will not persist across reboot.
# virsh net-destroy default
2. To permanently disable the libvirtd default network from being created at boot:
# virsh net-autostart default --disable
Remove libvirtd default network
To permanently remove the libvirtd default network:
# virsh net-undefine default
To permanently disable the libvirtd service from starting at boot on RHEL5 and RHEL6:
# chkconfig libvirtd off
To permanently disable the libvirtd service from starting at boot on RHEL7:
# systemctl disable libvirtd.service
