近日服务器安装CentOS8操作系统，想在这台机器安装KVM虚拟机。需要配置网桥，以方便虚拟机能够局域网中的其他机器处于同一网段相通。

Bridge（网桥）是 Linux 上用来做 TCP/IP 二层协议交换的设备，与现实的交换机功能相似。网桥设备实例可以和 Linux 上其他网络设备实例连接。当有数据到达时，网桥会根据报文中的 MAC 信息进行广播、转发、丢弃处理。

此前有写一篇文章讲述CentOS7配置桥接的，直接使用增加、修改 /etc/sysconfig/network-scripts/ifcfg-*配置文件的方式（有兴趣可通过文末链接阅读）。CentOS8中，已经默认不使用network.service管理网络了，默认采用NetworkManager.service管理，本文采用nmcli工具来配置网桥，可以让你更加方便快捷。

nmcli工具博大精深，是很好的网络管理工具～～～

 

在讲述配置的过程中，实时查看现象，以便更直观了解整个过程。

 

查看网络脚本目录，只看到以太网卡eno1的配置：

[root@server ~]# ls -al /etc/sysconfig/network-scripts/
total 8   
drwxr-xr-x. 2 root root   24 Oct  6 22:27 .
drwxr-xr-x. 7 root root 4096 Oct  6 23:15 ..
-rw-r--r--. 1 root root  308 Oct  6 22:27 ifcfg-eno1

查看以太网卡配置文件ifcfg-eno1的内容：

[root@server ~]# cat /etc/sysconfig/network-scripts/ifcfg-eno1 

TYPE=Ethernet
PROXY_METHOD=none
BROWSER_ONLY=no
.
.
.

查看当前连接：

[root@server ~]# nmcli connection 

NAME    UUID                                  TYPE      DEVICE 
eno1    ce6dd316-b6a9-4e58-9032-e0c1b3fcf1b0  ethernet  eno1   
virbr0  979aeccf-7002-4b27-853b-ca0faddf7f0d  bridge    virbr0

新建网桥，名字为br0：(关键步骤1)

[root@server ~]# nmcli connection add type bridge con-name br0 ifname br0 autoconnect yes
Connection 'br0' (6d7894dc-ccb0-45a6-9347-940128de7efa) successfully added.

这时这时/etc/sysconfig/network-scripts目录已经新增一个文件ifcfg-br0

查看连接：[root@server ~]# nmcli connection 

NAME    UUID TYPE DEVICE 

eno1 ce6dd316-b6a9-4e58-9032-e0c1b3fcf1b0 ethernet eno1

virbr0 979aeccf-7002-4b27-853b-ca0faddf7f0d bridge virbr0

br0 6d7894dc-ccb0-45a6-9347-940128de7efa bridge br0

网桥br0桥接至eno1：（关键步骤2）

[root@server ~]# nmcli connection add type bridge-slave ifname eno1 master br0

Connection 'bridge-slave-eno1' (b1788643-bdbb-4f24-adde-265462f172fc) successfully added.

这时/etc/sysconfig/network-scripts目录已经自动新增一个文件ifcfg-bridge-slave-eno1

查看连接：

[root@server ~]# nmcli connection 

NAME               UUID                                  TYPE      DEVICE 
eno1               ce6dd316-b6a9-4e58-9032-e0c1b3fcf1b0  ethernet  eno1   
virbr0             7bbff2fd-12e1-4e9c-8cd6-9f0bd14ad35e  bridge    virbr0 
br0                6d7894dc-ccb0-45a6-9347-940128de7efa  bridge    br0    
bridge-slave-eno1  b1788643-bdbb-4f24-adde-265462f172fc  ethernet  --

查看网络：

[root@server ~]# ifconfig 
eno1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500        inet 192.168.1.100  netmask 255.255.255.0  broadcast 192.168.1.255        inet6 fe80::548:8ed0:e2e:51cd  prefixlen 64  scopeid 0x20<link>        ether 00:d8:61:12:34:61  txqueuelen 1000  (Ethernet)        RX packets 4247  bytes 1606152 (1.5 MiB)        RX errors 0  dropped 0  overruns 0  frame 0        TX packets 1895  bytes 350509 (342.2 KiB)        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0        device interrupt 16  memory 0xdf000000-df020000
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536        inet 127.0.0.1  netmask 255.0.0.0        inet6 ::1  prefixlen 128  scopeid 0x10<host>        loop  txqueuelen 1000  (Local Loopback)        RX packets 220  bytes 20176 (19.7 KiB)        RX errors 0  dropped 0  overruns 0  frame 0        TX packets 220  bytes 20176 (19.7 KiB)        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
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:cc:69:3d  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

关闭eno1：（关键步骤3）

[root@server ~]# nmcli connection down eno1

Connection 'eno1' successfully deactivated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/2)

打开网桥br0：​​​​​​​（关键步骤4）

[root@server ~]# nmcli connection up br0

Connection successfully activated (master waiting for slaves) (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/4)

注意：如果这个过程是远程SSH或VNC操作的，需要耐心等信息返回～

查看连接（可以看到网桥已经生效）：

[root@server ~]# nmcli connection 

NAME               UUID                                  TYPE      DEVICE 
br0                6d7894dc-ccb0-45a6-9347-940128de7efa  bridge    br0    
bridge-slave-eno1  b1788643-bdbb-4f24-adde-265462f172fc  ethernet  eno1   
virbr0             7e63fed2-6839-43e0-9580-636729506f8f  bridge    virbr0 
eno1               ce6dd316-b6a9-4e58-9032-e0c1b3fcf1b0  ethernet  --

查看网络：

[root@server ~]# ifconfig 
br0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500        inet 192.168.1.100  netmask 255.255.255.0  broadcast 192.168.1.255        inet6 fe80::d0f2:879:9ecf:f907  prefixlen 64  scopeid 0x20<link>        ether 00:d8:61:12:34:61  txqueuelen 1000  (Ethernet)        RX packets 200  bytes 74916 (73.1 KiB)        RX errors 0  dropped 0  overruns 0  frame 0        TX packets 72  bytes 10614 (10.3 KiB)        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
eno1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500        ether 00:d8:61:12:34:61  txqueuelen 1000  (Ethernet)        RX packets 4526  bytes 1697104 (1.6 MiB)        RX errors 0  dropped 0  overruns 0  frame 0        TX packets 2026  bytes 367827 (359.2 KiB)        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0        device interrupt 16  memory 0xdf000000-df020000
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536        inet 127.0.0.1  netmask 255.0.0.0        inet6 ::1  prefixlen 128  scopeid 0x10<host>        loop  txqueuelen 1000  (Local Loopback)        RX packets 256  bytes 23716 (23.1 KiB)        RX errors 0  dropped 0  overruns 0  frame 0        TX packets 256  bytes 23716 (23.1 KiB)        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
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:cc:69:3d  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

网桥可以使用了。如不再使用网桥，可关闭，再重新打开eno1即可。