Setting up a kvm bridge on fedora 26.

A network  connects more network segments. A  software bridge behaves like a virtual network switch to which any physical or virtual devices can be connected.

1.Adding a bridge.

#brctl addbr br0

Check the bridge status.

#brctl show | grep br0
br0 8000.000000000000 no

2.Create a configuration file for the bridge and add  enp9s0 to it.

# brctl addif br0 enp9s0

Configuration for enp9s0
$ cat /etc/sysconfig/network-scripts/ifcfg-enp9s0
TYPE=Ethernet
PROXY_METHOD=none
BROWSER_ONLY=no
BOOTPROTO=none
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=yes
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=yes
IPV6_FAILURE_FATAL=no
IPV6_ADDR_GEN_MODE=stable-privacy
NAME=enp9s0
UUID=dafcc998-f948-39e5-9d0a-041dd2188707
ONBOOT=yes
AUTOCONNECT_PRIORITY=-999
DEVICE=enp9s0
#IPADDR=192.168.15.15
#PREFIX=20
#GATEWAY=192.168.0.4
IPV6_PRIVACY=no
DNS1=4.2.2.2
DNS2=8.8.8.8
DOMAIN=server.sand.box
ZONE=
BRIDGE=br0

Configuration for br0

DEVICE="br0"
ONBOOT=yes
TYPE=Bridge
BOOTPROTO=static
IPADDR=192.168.15.15
NETMASK=255.255.255.240
BROADCAST=192.168.15.255
STP=no
PROXY_METHOD=none
BROWSER_ONLY=no
PREFIX=28
GATEWAY=192.168.0.4
DNS1=4.2.2.2
DNS2=8.8.8.8
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=no
NAME="br0"
UUID=d2d68553-f97e-7549-7a26-b34a26f29318

#check bridge

#brctl show | grep br0
br0 8000.001c2301fbdc no enp9s0

###additionally you can add gateway in /etc/sysconfig/network
GATEWAY=192.168.0.4