Re: [libvirt-users] Need help with [virt net-create]

<Srinivas_G_Gowda@dell.com>
Tue, 20 May 2014 14:20:57 -0000

> Hmm, assuming we're both looking at the same diagram, I think
> your interpretation is wrong. Figure 18.4 (under section 18.3.1)
> is showing one virtual network (192.168.122.0/24) with two guests
> attached to it. I don't see any examples there which describe
> setup for 2 virtual networks.
Yes, I see my mistake now. Thanks for clarifying.


> Ok, so the virtual network NAT feature in libvirt doesn't
> include network teaming directly. The NAT based setup you've
> got in the XML causes libvirt to create a linux software
> bridge and connect guest TAP devices to that. Note that no
> physical network is enslaved in that bridge - only guest
I guess, PCI pass-through is the only mode in which I can truly see the link
status of a nic inside a VM ?




Thanks,
G
________________________________________
From: Daniel P. Berrange [berrange@redhat.com]
Sent: Tuesday, May 20, 2014 7:19 PM
To: Gowda, Srinivas G
Cc: libvirt-users@redhat.coms
Subject: Re: [libvirt-users] Need help with [virt net-create]

On Tue, May 20, 2014 at 06:35:54AM -0700, Srinivas_G_Gowda@dell.com
wrote:
> Thanks Daniel.
>
> Why was I trying to do something like this ?
> Two reasons
>
> 1. I was referring to ( Figure 18.4. Virtual network switch running
dnsmasq)
>
https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html-single/Virtualization_Administration_Guide/index.html#sect-network-protocols
>
>    that appears to be two virtual nics sharing the same IP range .. !!!

Hmm, assuming we're both looking at the same diagram, I think
your interpretation is wrong. Figure 18.4 (under section 18.3.1)
is showing one virtual network (192.168.122.0/24) with two guests
attached to it. I don't see any examples there which describe
setup for 2 virtual networks.

> 2. was playing around "Network teaming" in a VM. But this
>    doesnt seem to work. Please dont beat me around the use
>    cases for this :)

Ok, so the virtual network NAT feature in libvirt doesn't
include network teaming directly. The NAT based setup you've
got in the XML causes libvirt to create a linux software
bridge and connect guest TAP devices to that. Note that no
physical network is enslaved in that bridge - only guest
NICs. Traffic from the bridge to the LAN is forwarded at
the IP level. So if your host has been configured with
bonding, eg you have eth0 and eth1 configured into bond0
and have setup your hosts public IP on bond0, then the
NAT routing should automatically go to bond0.

So don't think creating multiple virtual networks really
does anything useful for network teaming. ie If you've setup
your host OS with bonding, then a single libvirt virtual
network should suffice.