KVM networking

eyemole80 · 02-18-2010, 05:22 AM

HI Friends,
I am trying to setup a hardware virtual machine on my Dell Laptop having wireless network card in it. I know there is no bridging support in wireless card, so I am using the routing techniques but thats not working.
I do not want to use "net user" mode of working as it is slow. So I am trying only TUN/TAP mode of netwroking.

Scenario is:
Laptop is running Fedora-12 X64
Laptop is connected with internet using WIFI card. WIFI IPADDR = 192.168.1.64/24 (DHCP). Default GW = 192.168.1.254
Created a tap interface "tap0" and gave it IPADDR = 192.168.100.50/24 (static IP)
Enabled IPV4 forwarding in kernel.

Launched the VM machine (Suse Linux). Gave it a static IP = 192.168.100.20/24, default route set to = 192.168.100.50

Now VM can ping to 192.168.100.50 and 192.168.1.64 , but it cannot ping to 192.168.1.254 or any other internet IP.

Error while trying to ping 192.168.1.254 is :
dst host unreacheble , error code 10

PS: I am able to ping any other internet IP from Host machine (i.e. Fedora-12)

Could someone suggest , where things are wrong?

HasC · 02-18-2010, 06:32 AM

Probably the packets flow OK from your VM to your GW = 192.168.1.254. But does your gateway know how to reach your VM? Probably not.

Instead of configuring your gateway, you could set up IP Masquerading in your host firewall.

eyemole80 · 02-18-2010, 06:51 AM

oops . you are right , I forgot the very basic thing.

Okay one more doubt . Proxy ARP can also be used in this scenario.

So what would be appropriate (more in terms of speed), using Proxy ARP or IP Masq ?

HasC · 02-18-2010, 06:55 AM

Quote:

Originally Posted by eyemole80

So what would be appropriate (more in terms of speed), using Proxy ARP or IP Masq ?

Don't know, because I don't know about proxy-arp.

I've been using both bridged and routed (and NATed) networking with QEMU/KVM, and I like bridging the most - the easier to implement, once you understand how it works. But that's my opinion, of course.

Chuck56 · 02-18-2010, 09:51 AM

You almost got it. You need both tuntap AND brctl to bridge the host's wireless interface with the KVM guest's tap interface. If I remember correctly, tap interfaces are also built into qemu and qemu-kvm if you don't want to use tuntap.

Start up the host bridge:

Code:

      ip addr flush wlan0
      ifconfig wlan0 0.0.0.0

      brctl addbr br0
      brctl stp br0 off
      brctl setfd br0 1
      brctl sethello br0 1
      brctl addif br0 wlan0

      tunctl -t tap0 -u kvm
      ifconfig tap0 0.0.0.0

      brctl addif br0 tap0

      dhclient br0

Shut down the host bridge:

Code:

      brctl delif br0 tap0
      tunctl -d tap0

      brctl delif br0 wlan0
      ip addr flush br0
      ifconfig br0 down
      brctl delbr br0

      ifconfig wlan0 0.0.0.0

      dhclient wlan0

You can replace the "-u kvm" with your system's KVM username and use dhcpcd instead of dhclient.

YMMV!

eyemole80 · 02-18-2010, 10:02 AM

Thanks Chucks,
But I cannot use bridging in wireless card as it is not supported in my wireless card. I have to use other methods only.

Chuck56 · 02-18-2010, 10:25 AM

Quote:

Originally Posted by eyemole80

Thanks Chucks,
But I cannot use bridging in wireless card as it is not supported in my wireless card. I have to use other methods only.

Is brctl installed on your system? I don't think it cares what wireless or ethernet card you have.