Various tool:
ifconfig ( and a file # if configuration )
brctl ( bridge-utils package) create bridge, it will be attach to a "host interface" and will have an IP@, tipical usage: mgt bridge or second interface/back up link
virsh ( libvirt ) create virtual network, internal vbridge, only between VM.
nmcli ( CLI version of networkmanager )
ip addr ... ( replacing ifconfig ) configure l2 and l3 parameters
[root@hp8300 me]# nmcli device
[root@hp8300 me]# nmcli connection
br0 is connected thru eno1 to the LAN ( used for management )
Create a virtual network with virsh
main directory: /etc/libvirt/qemu/networks/
virsh net-define virbr1.xml
virsh net-start virbr1
virsh net-autostart virbr1