[clug] KVM Bridge networking - Update 2 - Now IPv6 stack never gets disabled, only enabled by systemd-networkd

Robert Edwards bob at cs.anu.edu.au
Sun Apr 12 01:02:10 UTC 2020

On 12/4/20 12:07 am, George at Clug via linux wrote:
> Due to my error,  my answer to Michael's question to me did not make
> it to the CLUG list. (I hope the below more clearly explains my
> original question?)
> "I want "several isolated network bridges" on the KVM host, that are
> isolated from both the host KVM server, and isolated from other the
> bridges on the host KVM server.
> The isolated network bridges are connected to NICs that are connected
> to physical switches, and connecting to other physical and virtual
> servers."
> If the above does not clearly explain what I am asking, please ask me
> to provide further detail about what it is you don't understand.

Hi George,

I'm not going to include all of your lengthy posting in my reply. I need
to summarise what I think you are asking: You have an Ubuntu 18.04 host
running KVM with some guests. You want to attach some physical NICs
to some bridges for some of the guests, but not to the host system. But
the host system is still allocating IPv6 addresses on these bridges?

Firstly, Ubuntu 18.04 uses netplan to configure networking, but your
scripts seem to be using the Debian standard /etc/network/interfaces
scripts. Are you sure that you have the correct configuration scripts?

I have done what I think you are attempting with Linux Containers on a
Debian host. I set the physical NIC to "manual" configuration, which
tells the ip[up|down] scripts to not configure anything on them, then
attach them to the respective bridge with brctl add commands.

Also, with containers, it is possible to give the whole NIC to a guest
so that the host doesn't see it at all. Then it is up to the guest as
to how to configure it (including adding it to a bridge). You might be
able to do the same with KVM.

I hope this might help.

Bob Edwards.

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