Re: [Xen-users] Add independent interface from domU to internal bridge?

["Todd Deshane" <deshantm@xxxxxxxxx>]

On Sat, Oct 4, 2008 at 1:55 PM, Xenu13542 <xenu@xxxxxxxxxxxxxx> wrote:
> Hi,
>
> I have what I believe is an elementary problem, but I haven't yet figured
> out the solution.
>
> Within my domU host, I have a bridge named "net1". There is no routing
> performed between the real LAN and this bridge, intentionally. I have a
> virtual machine that connects to the bridge. It seems to work fine, (in fact
> I have several and I can bring them all up and they can communicate with
> each without incident).
>
> My domU host has a single physical network interface which sits on my LAN
> and provides internet access for the domU host only (so I can send email,
> browse the web, etc, from domU).
>
> What I don't understand is how to do is to add another, uh, virtual NIC that
> connects my domU host to the "net1" bridge that runs within it but that does
> not require connecting the LAN and the "net1" virtual bridge.
> Nearly all the documentation I have read is written from the point of view
> where the virtual network will be routed to the LAN via domU. It always just
> works with the built-in scripts, everyone's happy. If I recall correctly, my
> implementation worked like this in the beginning, but ultimately in my case
> this is undesirable so I created my own bridges and altered the guest
> systems to utilize those. I deleted the bridges created by the xen
> scripts/distributions and disabled the built in DHCP/DNS server some time
> ago, because I want this to come from a virtual machine on the net1 bridge.
> DomU's role is to provide a virtual world to run in only, not services to
> the guest systems.
> Other documents I've read suggest that I can achieve domU connectivity to
> the "net1" bridge by adding either the physical NIC or an alias of the
> physical NIC to the "net1" bridge using brctl. Anytime I manipulate the
> physical NIC in domU I lose LAN connectivity which is unacceptable.
> I have tried enabling the dummy ethernet module via modprobe facilities but
> it seems to have no effect, or I don't know how to interact with it. (It's
> been a while since I worked this angle and I don't recall what I did.)
> In at least one other document it seems that I could use `ip' to replace the
> dummy ethernet module using ip but it ultimately required an ethernet
> device. That seems to be precisely my problem, I don't have an ethernet
> device in this machine that isn't already busy doing something. Is that the
> answer? Must I have a separate physical ethernet device for every internal
> bridge that I want to connect to?
>
> Trying to Google this problem is almost as frustrating as the problem. My
> attempts to search invariably match documentation for common setups which I
> don't appear to have.
> For what it's worth, I'm running Fedora Core 8/Xen 3; 2.6.21-2950.fc8xen
> (supplied via the Fedora distribution)
> Any direction that might help me resolve this problem is greatly
> appreciated.
>

You can use a dummy device in dom0 as a bridge and give it to the guest
without having a physical device associated with it.

http://www.debian-administration.org/articles/360
http://wiki.xensource.com/xenwiki/XenNetworking
http://runningxen.com/resources/#chapter10

Cheers,
Todd

-- 
Todd Deshane
http://todddeshane.net
check out our book: http://runningxen.com

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