libvirt users - Jun 2010 - Some missunderstanding in the wiki page

Hi,

I'm not in the list and I just would like to comment it to the comunity. So,
if someone want to contact me, make CC to me in the reply.

The wiki page [1] talk about networking, and show two typical configurations:
"virtual network" and "shared physical device". 

The shared physical device has an error or something that could make confused, 
I think. What I want to say? In my case, I have a box with several nics, and 
I want to speciffy that ethX should be used exclusively but virtual domain X.

The documentation is clear in this: The NAT based connectivity is useful for 
quick & easy deployments, or on machines with dynamic/sporadic networking 
connectivity. More advanced users will want to use full bridging, where the 
guest is connected directly to the LAN. 

The configuration (I have follow only the debian/ubuntu steps) shows that br0 
has assigned an IP. I did the mistake to try to assign the same IP in the 
guest network configuration, I understand that, and obviously it doesn't
work
(duplicate IPs). So, to me, it would me more clear if the br0 interface has 
no IP. In my case, I have two nics: eth0 the interface for the host and eth1 
for the guest. The eth1 part in my network/interfaces is:

...
auto eth1
iface eth1 inet manual

auto br0
iface br0 inet manual
        bridge_ports  eth1
        bridge_stp    on
        bridge_maxwait  0
        bridge_fd       0
...

and then in the guest you configure the IP as you want. In the host, eth1 (or 
whatever interface you bridge) has no IP, so it's not used, and the guest 
uses completely.

What do you think?

Regards,

Leo


[1] http://wiki.libvirt.org/page/Networking

On 30/06/10 10:35, Leopold Palomo-Avellaneda wrote:
> The configuration (I have follow only the debian/ubuntu steps) shows that
br0
> has assigned an IP. I did the mistake to try to assign the same IP in the
> guest network configuration, I understand that, and obviously it
doesn't work
> (duplicate IPs). So, to me, it would me more clear if the br0 interface has
> no IP. In my case, I have two nics: eth0 the interface for the host and
eth1
> for the guest. The eth1 part in my network/interfaces is:
>
> ...
> auto eth1
> iface eth1 inet manual
>
> auto br0
> iface br0 inet manual
>          bridge_ports  eth1
>          bridge_stp    on
>          bridge_maxwait  0
>          bridge_fd       0
> ...
>
> and then in the guest you configure the IP as you want. In the host, eth1
(or
> whatever interface you bridge) has no IP, so it's not used, and the
guest
> uses completely.
The common configuration that the wiki is documenting is presumably the 
case where the host has a single ethernet interface that is shared by 
the host and the guests. In that configuration the bridge does have an 
address, which is the address of the host machine.

Basically a bridge is like a virtual ethernet switch inside your 
machine, where one port is connected to each device that is enslaved to 
it and another port is connected to the kernel's IP stack - that port 
appears as the brN interface and can have an IP address (for the host) 
assigned to it.

Tom

-- 
Tom Hughes (tom at compton.nu)
http://compton.nu/