A network bridge is nothing but a device that joins two local networks into one network. It works at the data link layer (layer 2 of the OSI model). Network bridges often used with virtualization software. For example, popular software such as KVM, LXD, or Docker users can configure bridges instead of NAT-based networking. The nmcli command-line tool can create a persistent bridge configuration without editing any files. This page shows how to create a bridge interface using the Network Manager command-line tool called nmcli on an Ubuntu 20.04 LTS Linux server.
Tutorial requirements | |
---|---|
Operating system/app | Ubuntu 18.04/20.04 LTS server |
Root privileges required | Yes |
Difficulty | Easy (rss) |
Estimated completion time | 5m |
Ubuntu 20.04 add network bridge (br0) with nmcli
The procedure to create and add a bridge interface on Ubuntu version 20.04 is as follows when you want to use Network Manager:
- Open the Terminal app or log in using the ssh command
- Find out information about the current Ubuntu network connection:
sudo nmcli con show - Then, add a new bridge called br0:
sudo nmcli con add ifname br0 type bridge con-name br0 - Create a slave interface for br0 using enp0s31f6 NIC:
sudo nmcli con add type bridge-slave ifname enp0s31f6 master br0 - Turn on br0 interface to get an IP via DHCP:
sudo nmcli con up br0 - Static IP settings are discussed below for the br0 interface
Let us see all examples and instructions in detail to create a network bridge in Ubuntu Linux version 20.04 LTS server.
Prerequisite for creating a Linux network bridge on Ubuntu 20.04
First thing, obtain information about the current Ubuntu Linux interface and IP address as we need this information later. Hence, type the following commands:
$ nmcli con show
$ nmcli connection show --active
Outputs:
NAME UUID TYPE DEVICE ETH0 71a189f2-9cb9-49f0-8464-37a6801740e3 ethernet enp0s31f6
So my server has an “ETH0” which uses the enp0s31f6 Ethernet interface. I am going to set up a bridge interface named br0 and add (enslave) an interface to enp0s31f6.
Step 1 – Creating a network bridge named br0
The syntax is:
$ sudo nmcli con add ifname br0 type bridge con-name br0
$ sudo nmcli con add type bridge-slave ifname enp0s31f6 master br0
$ nmcli connection show
Step 2 – Disable or enable STP for network bridge
The primary purpose of Spanning Tree Protocol (STP) is to ensure that you do not create loops when you have redundant paths in your network. We can disable STP or enable as follows for br0:
$ sudo nmcli con modify br0 bridge.stp no
## Ubuntu 20.04 Linux nmcli command to enable STP with br0 ##
$ sudo nmcli con modify br0 bridge.stp yes
## Verification ##
$ nmcli con show
$ nmcli -f bridge con show br0
Outputs:
bridge.mac-address: -- bridge.stp: yes bridge.priority: 32768 bridge.forward-delay: 15 bridge.hello-time: 2 bridge.max-age: 20 bridge.ageing-time: 300 bridge.group-forward-mask: 0 bridge.multicast-snooping: yes bridge.vlan-filtering: no bridge.vlan-default-pvid: 1 bridge.vlans: --
Step 3 – Set up static or DHCP based IP for network bridge interface
We have not allocated any static IP address to our br0 interface. Hence, if the DHCP server is available, it should provide IP addresses and other settings. However, on servers, we typically set up a static IP address. In this example, I am converting existing enp0s31f6 IP network settings to br0 settings as follows:
IPv4 br0 settings
$ sudo nmcli connection modify br0 ipv4.addresses '192.168.2.25/24'
$ sudo nmcli connection modify br0 ipv4.gateway '192.168.2.254'
$ sudo nmcli connection modify br0 ipv4.dns '192.168.2.254'
$ sudo nmcli connection modify br0 ipv4.dns-search 'sweet.home'
$ sudo nmcli connection modify br0 ipv4.method manual
IPv6 br0 settings
$ sudo nmcli connection modify bridge0 ipv6.addresses 'Your-Static-IPv6-Address'
$ sudo nmcli connection modify br0 ipv6.gateway 'Your-Static-IPv6-Gateway-Address'
$ sudo nmcli connection modify br0 ipv6.dns 'Your-Static-IPv6-DNS'
$ sudo nmcli connection modify br0 ipv6.dns-search 'sweet.home'
$ sudo nmcli connection modify br0 ipv6.method manual
Step 4 – Enable br0 network bridge interface on Ubuntu Linux
So far, we configured required network settings. It is time to turn it on our br0:
$ sudo nmcli con up br0
$ nmcli con show
Wait for some time to activate settings.
Step 5 – Verification network bridge settings
Use the ip command to view the IP settings for br0 bridge on Ubuntu box:
$ ip a s
$ ip a s br0
You can remove enp0s31f6 as br0 got a static IP address itself as enp0s31f6 will be in forwarding state:
$ sudo nmcli connection delete enp0s31f6
## or ##
$ sudo nmcli connection delete ETH0
Here is how it looks using the ip command:
$ nmcli connection show
$ ip a show br0
$ nmcli device
## interface active and works with br0 ##
$ ip a show enp0s31f6
$ ip r
## Check Internet and local LAN connectivity using ping command ##
$ ping -c 4 www.cyberciti.biz
$ ping -c 4 192.168.2.25
Show the link status of Ethernet devices and bridge devices on Ubuntu Linux machine:
$ ip link show master br0
$ bridge link show
$ bridge link show dev enp0s31f6
Conclusion
In this tutorial, you learned how to add and create a Linux Network Bridge on Ubuntu 20.04 LTS server. See nmcli docs online for more info.
- Debian Linux: Configure Network Interfaces As A Bridge / Network Switch
- OpenBSD: Configure Network Interface As A Bridge / Network Switch
- How To PFSense Configure Network Interface As A Bridge / Network Switch
- FreeBSD: NIC Bonding / Link Aggregation / Trunking / Link Failover
- How To Setup Bridge (br0) Network on Ubuntu Linux 14.04 and 16.04 LTS
- Ubuntu setup a bonding device and enslave eth0+eth2
- Setup Bonded (bond0) and Bridged (br0) Networking On Ubuntu
- Ubuntu 20.04 add network bridge (br0) with nmcli command
- CentOS 8 add network bridge (br0) with nmcli command
- How to add network bridge with nmcli (NetworkManager) on Linux
- Set up and configure network bridge on Debian Linux
🐧 6 comments so far... add one ↓
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I think there’s a limitation with the standard Linux bridge when working with wireless adapters. Actually I think it’s a limitation with wireless link layer then authentication and trying to bridge Ethernet layer 2 over that authenticated stack if you get me.
Hi, i have trouble withe getting an ip from the DHCP server to the bridge while the vm does get an ip. i would appreciate if you explain how to activate the br to work with dhcp , not based on if my dhcp server works in general (I’m on wireless). Thanks
BTW: you have a typo in commands (missing con-name option) :
> Then, add a new bridge called br0:
sudo nmcli con add type bridge ifname br0
later in the page there is a proper syntax including “con-name” :
sudo nmcli con add ifname br0 type bridge con-name br0
Fixed it. Thanks for the tip and I appreciate your feedback.
What is exactly ‘sweet.home’ in
sudo nmcli connection modify br0 ipv4.dns-search 'sweet.home'
Where does this value come from and what is the purpose/usage of this setting?
Thanks
That is my own domain search name set up in my DHCPD. So instead of typing ssh ‘mylaptop.sweet.home’, I type ‘mylaptop’. You can ignore sudo nmcli connection modify br0 ipv4.dns-search ‘sweet.home’ if you don’t have such fancy config.