On 9/9/20 7:13 AM, Paul van der Vlis wrote: 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) 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). 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>

I am trying to understand KVM networking a little better and have noted that the "virbr0" network interface (the default KVM bridge) comes with another device named "virbr0-nic". The same kind of pair comes with each new bridge you may create via the "virtual machine manager" (and assumingly other KVM tools alike) Like "virbr1" comes in a pair with "virbr1-nic" (the *-nic interface is being created automatically (and I assume will disapear automatically if you remove the parent interface) Can anybody kindly explain how these pairs are related to each other and/or work together? thanks ... Gunnar

ok, thanks for the explainer. On 04.01.21 12:20, Daniel P. Berrangé wrote: