[SOLVED] KVM / QEMU - Bridge interface

sluggeek · n00b Joined: 21 May 2020 Posts: 36 Location: France

Hi everyone.

I try switching from Vbox to QEMU. I just have one issu.

I want my VM in the network of the host. So I need a bridge connection, like I do with Vbox.

I have delete the "default" virtual network in qemu

What I do (enp39s0 is my physical interface)

ip link add name br0 type bridge
ip link set enp39s0 master br0
ip link set br0 up

After that I proper configure VM to use br0.
And that works, my VM is on the same network : i can ssh, ping ...

BUT : my host cant use enp39s0 anymore ...

The problem is after the command
ip link set enp39s0 master br0 : after this the connection is lost.

Do you have any idea to have both the VM and the Host using enp39s0.

I apologise for my terrible english

Thx

mike155 · Posted: Sat Oct 23, 2021 1:47 pm Post subject:

I don't know the syntax of the new 'ip link' commands. But I can show you how I set up my bridge for QEMU with the traditional commands:

sluggeek · n00b Joined: 21 May 2020 Posts: 36 Location: France

I thanks to anwser.

I had always the same problem. After the brctl addif br0 enp39s0, the enp39s0 lost the connection

mike155 · Posted: Sat Oct 23, 2021 3:39 pm Post subject:

Without the bridge, the interface enp39s0 must be configured with your IP address.

With the bridge, the interface br0 must be configured with your IP address.

So yes, it is to be expected that you lose the connection if you add enp39s0 to your bridge. Configure br0 with your IP address after you added enp39s0 to your bridge - and you won't lose the connection.

sluggeek · n00b Joined: 21 May 2020 Posts: 36 Location: France

Hi Mike,

Thanks for the help. It works now

My mistake was to try to use "bridge" before understand how I works. I got it now.

sluggeek · n00b Joined: 21 May 2020 Posts: 36 Location: France

If somebody else have the same issu, here is the recipe :

Use sudo - Router is DHCP - physical interface in enp39s0

#Creation of bridge interface br0 and activation
ip link add name br0 type bridge
ip link set br0 up

#Activate enp39s0 if needed (you can't bridge a down interface).
ip link set enp39s0 up

#Flushing ip address on enp39s0 (if needed)
ip addr flush dev enp39s0

#Link enp39s0 to br0
ip link set eth0 master br0

#Obtain an IP for br0
dhclient -v br0

# check internet still working
ip a
ping www.google.com

After, configure the VM to use br0
-> network source : Brigde device
-> device name : br0

Launch the VM. Sometimes the VM internet connection works immediatly, sometimes it take 30s, don't panic