Cant ping Host and VM vice versa [KVM]

decenter · 07-09-2013, 08:49 AM

Hello,

I have installed KVM in Linux Deepin desktop 12.12. I created Cent OS VM and assigned static private IP to it. I can ping to internet and other local computer's IP address from the VM, but I can't ping my host (my PC where I installed KVM) IP. My host IP has separate static IP. Also I cannot ping to VM from the host.

The connection type for VM is bridged. Screenshot: http://i.imgur.com/jpneLRl.png?1

Any idea?

Thanks.

asimba · 07-09-2013, 09:05 AM

Are they on same net

decenter · 07-09-2013, 09:07 AM

Hello,

Yes, they are on the same subnet. Infact the other local computers are also in the same subnet.

asimba · 07-09-2013, 09:49 AM

May I have IP's for both please (Virtual MAchine and Host)

decenter · 07-10-2013, 03:02 AM

Hello,

Sure.

Host IP : 192.168.20.181

VM IP : 192.168.20.201

I can ping other local computers around. One of its IP is 192.168.20.167

gradinaruvasile · 07-17-2013, 03:34 AM

I think this question was asked many times around here.

It will not work like this.

The (only?) way to have full network transparency with kvm is to use a pre defined bridge on the host - one working method ( i use it too) is to transfer the physical (say eth0) devices config to a bridge (br0) then use that bridge as a shared device in kvm/virt-manager.
For example i have:

Code:

$ brctl show
bridge name	bridge id		STP enabled	interfaces
br0		8000.94de80008b0c	no		eth0
							vnet0

vnet0 is a device created by kvm attached to my running vm. eth0 has no configuration - everything it had is transferred to br0. Every vm will have its own vnetX device when started - the IP address etc is controlled from within the vm.

Chuck56 · 07-17-2013, 07:28 AM

Quote:

Originally Posted by gradinaruvasile

I think this question was asked many times around here.

It will not work like this.

The (only?) way to have full network transparency with kvm is to use a pre defined bridge on the host - one working method ( i use it too) is to transfer the physical (say eth0) devices config to a bridge (br0) then use that bridge as a shared device in kvm/virt-manager.

It can work. When using macvtap for the VMs then use macvlan for the host. Then VM & host can "see" each other similar to the BR/TAP bridging method.

Code:

# as root - add macvlan to eth
ip addr flush eth0
ip link add link eth0 dev mvl0 type macvlan mode bridge
ip link set mvl0 addr 00:00:00:02:01:81 up
ip addr add 192.168.20.181 dev mvl0
ip route add default via 192.168.20.1 dev mvl0
# show the interfaces
ip addr
# show the routes
ip route

gradinaruvasile · 07-17-2013, 07:37 AM

Thats basically the same, correct me if its not. Does it persist after reboot?

Chuck56 · 07-17-2013, 07:44 AM

Quote:

Originally Posted by gradinaruvasile

Thats basically the same, correct me if its not. Does it persist after reboot?

No persistence after reboot. You could script it to run on start up.

gradinaruvasile · 07-17-2013, 07:53 AM

Does it have any tangible advantages over the standard bridging method?

Chuck56 · 07-17-2013, 09:14 PM

Quote:

Originally Posted by gradinaruvasile

Does it have any tangible advantages over the standard bridging method?

The upsides are numerous. Using macvtap/macvlan simplifies networking by decoupling the tap and the bridge. You can start a macvtap and gain network access with the VM without starting the macvlan for the host. You only need the macvlan if you need the VM and the host to see each other. The cli is simplified using route2 commands as a single tool to manipulate the macvtap, macvlans and default route. You don't have to use separate cli tools like brctl for the bridge and tunctl for the tap and route for the default route. The modules for macvtap, macvlan & tun modules are automatically loaded as dependencies of the vhost_net module used for virtio networks.

A downside is that qemu doesn't directly support macvtap yet so you have to use file descriptors for network access. That's handled for you if you use libvirt and requires a bit more effort if you use the cli. There may be other downsides but they don't jump out at me at the moment.