Bridging and KVM

[beaker_]

In reasoning why you needed them bridged, I may have read too much into the problem. Just use the Virtual Machine Manager, choose/add/configure you nic and select NAT'd.

Anyway I thought stevea's link explained it very well. Fedora and RedHat wrt qemu & kvm still use the virbr interface, right?

[stevea]

Originally Posted by beaker_

Why bridge when it will never be trustworthy?

Why wouldn't bridging be stable and trustworthy ?! I've used bridged (as in brctl) connections for commercial systems since the early 2.4 kernel days. I've used it in custom network hardware configs. My mail server is a VM connected by bridge. All of these work 100%.

Here is why brctl doesn't work with wifi. It's a 80211 stack usage issue.
http://www.linuxfoundation.org/colla...reless_card.21

Is there a reason why you don't route your virbr interface instead? Personally, I'd buy a nic and pull a wire.

One reason to not want route/NAT virbr connection is that the performance is a lot slower (but still decent). But it certainly avoids the 'wifi' can't bridge' problem. So *IF* you have a wired connection - yes you can improve net performance by just adding the wired connection to the bridge and using this bridge directly as your net interface (no routing, no NAT, just a software hub).

Originally Posted by geekaume

beaker,
I can't understand what you said. What do you mean by "why you don't route your virbr interface instead" ? Is there a way for me to have VMs accessing the network (and Internet) with a Wifi interface ?

I can't have a wire : my router is too far from the PC....

The default Fedora KVM configuration creates a virbr0 bridge just for the VMs and then it creates a tap/tun device for each VM that connects the VM to this bridge. Then it creates a virbr0 tap/tun that is NAT/routed to the (primary?) Host network (like your wifi).

You can change it but the default bridge is virbr0 with LAN range 192.168.122.*/24
The VMs can NAT to your LAN and even out to the Inet.
Your Host can access the VMs and the virbr0 LAN according to the iptables entries created (disables ping/icmp btw).
To access the VMs from across your LAN you need to add route entries to the other systems. You neet to route the address range for the VMs (192.168.122.*/24 by default) to the VM host.


Look at the virt-manager' virtual network setup screens.

[beaker_]

Originally Posted by stevea

Why wouldn't bridging be stable and trustworthy ?! I've used bridged (as in brctl) connections for commercial systems since the early 2.4 kernel days. I've used it in custom network hardware configs. My mail server is a VM connected by bridge. All of these work 100%.

Hmmm seamed clear at the time.., because we're discussing a wireless bridge.

At best he has about 2MBps through-put and he want's to split it between his host and X# of virtual machines. Yeah, he's not trying to shove 1G or 100M through it but I'll bet there will be too much crap/overhead sitting on the bridge... so would NM crap its pants and split, drop the connection all together, or would the AP drop you?

[jlpierce]

Originally Posted by stevea

Here is why brctl doesn't work with wifi. It's a 80211 stack usage issue.
http://www.linuxfoundation.org/colla...reless_card.21

Okay, so I guess I am confused by some of this wireless bridging discussion. I have 3 laptop computers, 2 have realtek wireless chips and the other is atheros and they use the stock Fedora 17 modules on boot. Virtualbox PUEL edition offers the option to bridge the wlan0 configuration and my windows guests function just fine.

So my question is this, why does Virtualbox offer to and successfully bridge the wireless connection with no additional effort but the kvm/qemu built in cannot?

Just curious.

[geekaume]

I am sorry but you lost me....

Someone earlier said that bridging does not work with most wifis. It means that it work with some wifis. What I would have to change to get this work (if I understood correctly : it can work in some cases) ?

I have a virbr0. How can I use that ? I didn't understand all Stevea's post.

thank you very much

[solo2101]

Originally Posted by stevea

Here is the answer .... bridging does NOT work with most wifis

http://www.linux-kvm.org/page/Networking

---------- Post added at 02:34 AM ---------- Previous post was at 01:53 AM ----------



Fail - you still cant bridge most wifis w/ Virtualbox, and it has kernel problems with some regularity.

really?

I wonder how mine is working then...

[solo2101]

I never had any problems with VBox and bridges before... but like everyone is been saying... it well might be my wireless card...

[solo2101]

Originally Posted by jlpierce

So my question is this, why does Virtualbox offer to and successfully bridge the wireless connection with no additional effort but the kvm/qemu built in cannot?

Just curious.

IMHO I think this is because kvm is design for server use (like VMware), while VBox is aimed for desktop use (like in laptops)... if you are setting a VM server that will hold multiple VMs, you will want to use KVM and bridging. I dont see why to use KVM on a laptop (except for the pourpuse of learning). Beside KVM console is not as snappier as VBox is.

[jpollard]

I though it was because virtualbox included it's own network routing layer...