On 9/9/20 7:13 AM, Paul van der Vlis wrote:
Hello,
I want to do some testing and I have removed two VM's from the bridge
what connects them to internet, and added them to another isolated
bridge what's not connected to internet. Problem is that I cannot reach
the other host in the isolated network.
Something like this:
virsh shutdown kvm66
virsh shutdown kvm68
brctl delif br0 vnet10 vnet6 # the interfaces of kvm66 and kvm68
brctl addbr br1
brctl addif br1 vnet10 vnet6
The delif and addif commands won't do anything if the guests are not
running (you've done "virsh shutdown", but that will either take some
time, or never be honored (depending on how the guest OS deals with
ACPI, I think)
Then I've replaced br0 to br1 in the XML of both VM's with "virsh edit".
Just be certain that each guest is either completely inactive (doesn't
show up in the output of "virsh list" when you edit, or at some point
after you've edited it (i.e. there must be a complete "virtual
powercycle" of the guest for the changes to take effect).
Then I did start the VM's using the serial console (no network):
virsh start --console kvm66
virsh start --console kvm68
I cannot ping from one machine to the other. Why??
I guess you're using <interface type='bridge'> ... right?
Since the bridge devices were created and are managed outside libvirt's
control, you need to do more than just create a bridge to get the
connected guests talking to each other. In particular, if the guests are
getting their IP addresses from DHCP, then you need to assign an IP
address to the bridge device, and run a DHCP server that is listening on
the bridge. (I'm curious what you used as the argument of the ping
command, if the guests didn't have an IP address...)
(Aside from that, a bridge created with brctl will disappear when the
host is rebooted, and not be recreated until you again enter the commands.)
If you want a simple way to create a bridge, start a dnmasq instance to
serve DHCP, and add iptables rules to prevent the guests from breaking
out of the isolated bridge, *and* as a bonus *re*create all of that
every time you reboot the host, you can create an isolated libvirt
virtual network, with a config file like the one here:
https://libvirt.org/formatnetwork.html#examplesPrivate
(editing to your taste for bridge name and IPv4 and IPv6 addresses). Put
that in a file (e.g. net.xml) and run (as root) "virsh net-define
net.xml; virsh net-start private; virsh net-autostart private".
Then define your guest interfaces with this:
<interface type='network'>
<source network='private'/>
...
</interface>
