Create A Network Bridge on CentOS 7 / RHEL 7

ADVERTISEMENT

Create A Network Bridge on CentOS 7 / RHEL 7
Create A Network Bridge on CentOS 7 / RHEL 7

Sometimes you may need to setup network bridge adapter in Linux; particularly during the configuration of KVM (Kernel-based Virtual Machine), and, also while setting up Linux containers. This bridge network allows virtual machines to have access to the external network and vice-versa, follow this guide to setup network bridge on CentOS 7 / RHEL 7.

Install Module:

CentOS 7 comes with bridging module loaded on system boot by default, verify it by using below command.

ADVERTISEMENT
Article will continue after the ad
# modinfo bridge
 filename:       /lib/modules/3.10.0-327.el7.x86_64/kernel/net/bridge/bridge.ko
 alias:          rtnl-link-bridge
 version:        2.3
 license:        GPL
 rhelversion:    7.2
 srcversion:     905847C53FF43DEFAA0EB3C
 depends:        stp,llc
 intree:         Y
 vermagic:       3.10.0-327.el7.x86_64 SMP mod_unload modversions
 signer:         CentOS Linux kernel signing key
 sig_key:        79:AD:88:6A:11:3C:A0:22:35:26:33:6C:0F:82:5B:8A:94:29:6A:B3
 sig_hashalgo:   sha256

If the module is not loaded, you can load it using the following command.

# modprobe --first-time bridge

Install bridge-utils for controlling the network adaptors.

# yum install bridge-utils -y

Create a Network Bridge:

To create a network bridge, create a file called “ifcfg-virbrN” replacing “N” with a number, such as “0” in the “/etc/sysconfig/network-scripts/“.

File doesn’t necessarily to be “virbrN“, you can also give a name like “brN

# vi /etc/sysconfig/network-scripts/ifcfg-virbr0

Place the following content into that file, modify it according to your environment.

DEVICE="virbr0"
BOOTPROTO="static"
IPADDR="192.168.12.10"
NETMASK="255.255.255.0"
GATEWAY="192.168.12.2"
DNS1=192.168.12.2
ONBOOT="yes"
TYPE="Bridge"
NM_CONTROLLED="no"

Now, it’s the time to modify the network configuration of the existing adaptor in such a way that it points to a bridge interface. In this guide, I will use my existing adaptor “eno16777736” for bridging.

# vi /etc/sysconfig/network-scripts/ifcfg-eno16777736

Place the content like below.

DEVICE=eno16777736
TYPE=Ethernet
BOOTPROTO=none
ONBOOT=yes
NM_CONTROLLED=no
BRIDGE=virbr0

Restart the network using the following command.

# systemctl restart network

Use ifconfig command to see interface details.

# ifconfig
eno16777736: flags=4163  mtu 1500
        inet6 fe80::20c:29ff:fe6a:692  prefixlen 64  scopeid 0x20
        ether 00:0c:29:6a:06:92  txqueuelen 1000  (Ethernet)
        RX packets 3822  bytes 302382 (295.2 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 192  bytes 42924 (41.9 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10
        loop  txqueuelen 0  (Local Loopback)
        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: flags=4163  mtu 1500
        inet 192.168.12.10  netmask 255.255.255.0  broadcast 192.168.12.255
        inet6 fe80::20c:29ff:fe6a:692  prefixlen 64  scopeid 0x20
        ether 00:0c:29:6a:06:92  txqueuelen 0  (Ethernet)
        RX packets 1454  bytes 109258 (106.6 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 179  bytes 34372 (33.5 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Reference:

Redhat Documentation

Thanks for reading, do let us know your thoughts in comments section.

ADVERTISEMENT

POSTS YOU MAY LIKE -:)

Share This Post

  • Charliemopps

    And if the interface is has a dynamic IP?

    • Replace it with this.

      DEVICE=”virbr0″
      BOOTPROTO=”dhcp”
      ONBOOT=”yes”
      TYPE=”Bridge”
      NM_CONTROLLED=”no”

  • techietubby

    Thanks very a very interesting and useful article. Just two small points:

    1. If you set NM_CONTROLLED to No you don’t see the entry under nmcli.

    2. Disabling NM_CONTROLL also breaks libvirt connections if the interface/connection is now hidden.

    I spent a long time getting this to work and found it best to create the bridge script first with a temporary IP and then reboot and check you can access both addresses. Make a copy of your work ethernet connection script from /etc/sysconfig/network-scripts, and then edit it as above.

    This way if you restart the network you should still be able to get in using the temp. IP.

    Reboot again and check, and if everything is working, just change the bridge IP back to the proper one and comment-out or remove the NM_CONTROLLED entries and reboot again and everything should be working as expected.

Shares