What is the virbr0 interface used for?

 virbr0 Link encap:Ethernet HWaddr a2:17:ea:e3:47:7e inet addr:192.168.122.1 Bcast:192.168.122.255 Mask:255.255.255.0 UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) 

can anyone tell me what this interface does and how I can change the IP address? I want to see if it is the reason my guests cannot connect.

5 Answers

The virbr0, or "Virtual Bridge 0" interface is used for NAT (Network Address Translation). It is provided by the libvirt library, and virtual environments sometimes use it to connect to the outside network.

It was likely bundles with a VM software you installed at some point. If you'd like to remove it, and you're sure nothing else depends on it, you can use the following command:

sudo brctl delbr virbr0 

(from UbuntuForums)

It is unlikely that the virtual bridge is affecting your guests' ability to connect to the Internet, though.

If you are unable to connect to the internet due to "vibr0" interface then follow the commands below

virsh net-destroy default virsh net-undefine default service libvirtd restart ifconfig 

For changing the ip address of virbr0 under ubuntu 12.04

 sudo cp /var/lib/libvirt/network/default.xml /tmp/default.xml sudo vi /tmp/default.xml # edit the ip address sudo virsh net-destroy default sudo virsh net-undefine default sudo virsh net-define /tmp/default.xml sudo virsh net-start default 

You could refer to:

I am using virtualbox 5.2.28 on ubuntu-16.04 and the config file is in /var/lib/libvirt/dnsmasq/default.conf

maybe you can always check the conf file location by checking the cmdline of the dnsmasq process.

To check the process number, port, and name.

sudo netstat -plant 

To check the cmdline and find from where it loads the configuration file use

cat /proc/<PID>/cmdline 

My answer is a mix of previous answers, but that's how I could make it to work for me:

cp /var/lib/libvirt/network/default.xml /tmp/default.xml vi /tmp/default.xml # edit the ip address sudo virsh net-destroy default sudo virsh net-undefine default # needed to avoid errors below sudo virsh net-define /tmp/default.xml sudo virsh net-start default rm /tmp/default.xml