[ovs-discuss] Connecting OVSs and hosts running on different VMs

[Scott Lowe]

Please see my responses inline, prefixed by [SL].


> On Nov 23, 2015, at 9:40 AM, David Gabriel <davidgab283 at gmail.com> wrote:
> 
> Your analysis is very good !
> What I want to get is that VM-A (or VM-B,C,D) runs on a separate VM  but if it is not feasible, I can adapt my scenario to the last figure you made :  
> VM-A      VM-B          VM-C      VM-D
>   |        |              |        |
> HostMachineVM1          HostMachineVM2
>   w/ OVS                  w/ OVS
>     |                        |
>     |                        |
>     +-------Hypervisor-------+
> I am using Ubuntu and VirtualBox. If you recommand other distribution/tool I will change my environment.
> Now could you please tell me how shall I proceed to ensure the connection in my topology?


[SL] Ubuntu+VirtualBox doesn't support nested virtualization, so you can't build this topology. You'd need to switch to Ubuntu+KVM (and configure KVM to use nested virtualization, which AFAIK is not the default) or use VMware Workstation on Linux (which does support nested virtualization). You are running Ubuntu on the host, so it's possible to go the Ubuntu+KVM route (but a fair amount more work, TBH). Unless you're really familiar with Ubuntu+KVM+Libvirt, the easiest route is probably to switch to VMware Workstation, which would allow you to build this topology used nested virtualization support.

There *may* be a way to break out VM-A/B/C/D into separate VMs, but as I pointed out to Hassan in a separate reply that would involve using bridges to connect VMs to where OVS was running, and that's not a configuration I've ever tested/used/verified.



> 2015-11-23 17:11 GMT+01:00 Scott Lowe <scott.lowe at scottlowe.org>:
> Please see my responses inline, prefixed by [SL].
> 
> 
> > On Nov 23, 2015, at 8:59 AM, David Gabriel <davidgab283 at gmail.com> wrote:
> >
> > Dear Scott,
> >
> > Thanks for reactivity.
> > Since I have only one physical machine so I want to create inside it :
> > 1- One VM representing OVS switch #1
> > 2- One VM representing OVS switch #2
> > 3- One VM representing the host machine #1 connected to OVS switch #1
> > 4- One VM representing the host machine #2 connected to OVS switch #2
> >
> > Then I have to ensure the connection between my 2 switches in one hand. On the other hand I have to connect switch #1 to host #1. And I have to do same witch switch 2 and host2
> > My scenario may be unusual but I have a limitation regarding physical equipment availability.
> >
> >     c1                  c2
> >        |                  |
> >        |                  |
> >        |                |
> >     |ovs1|--------------|ovs2|
> >        |                  |
> >        |                  |
> >        |                  |
> > HostMachine1   HostMachine2
> 
> 
> [SL] Before we go any further let's make sure we understand that OVS generally exists *inside* the hosts, so your diagram would typically look something more like this:
> 
> HostMachine1            HostMachine2
>   w/ OVS                  w/ OVS
>     |                        |
>     |                        |
>     +----Physical network----+
> 
> In your case, you want to run all this virtual because you have limited physical hardware. No problem. The diagram shifts slightly to look like this:
> 
> HostMachineVM1          HostMachineVM2
>   w/ OVS                  w/ OVS
>     |                        |
>     |                        |
>     +-------Hypervisor-------+
> 
> In this case, "hypervisor" could be Linux+KVM, Linux+Xen, ESXi, or any number of hosted type 2 hypervisors (VirtualBox, Fusion, Workstation, etc.). *IF* the hypervisor is a Linux variant, then you can use OVS there to provide connectivity between the VMs; otherwise, you are limited to whatever the hypervisor provides.
> 
> Taking this to the next level...*IF* your hypervisor supports what is known as nested virtualization, then you can run VMs inside the VMs so it looks something like this:
> 
> VM-A      VM-B          VM-C      VM-D
>   |        |              |        |
> HostMachineVM1          HostMachineVM2
>   w/ OVS                  w/ OVS
>     |                        |
>     |                        |
>     +-------Hypervisor-------+
> 
> In this sort of configuration, you can use OVS (inside HostMachineVM1 and HostMachineVM2) to provide networking connectivity to the nested VMs (VM-A through VM-D).
> 
> I *think* this last scenario is probably what you're seeking to do, but I could be wrong.
> 
> Does this help at all?
> 
> 
> 
> > 2015-11-23 16:42 GMT+01:00 Scott Lowe <scott.lowe at scottlowe.org>:
> > Please see my response below.
> >
> >
> > On Nov 23, 2015, at 8:37 AM, David Gabriel <davidgab283 at gmail.com> wrote:
> >>
> >> Dears,
> >>
> >> I am lookig to define a basic topology including 2 OVS switches and 2 hosts (each host is connected to one switch). These 4 components (switches ans hosts) are running in one separate VM. Please tell me how to connect them in order to ensure the communication in my basic network.
> >> I checked so many links in the Internet but I didn't find a holistic tutorial ...
> >> Regarding the controller I learn how to set it.
> >
> >
> > Generally speaking, OVS runs *in* the host, so I'm a bit unclear on what you're trying to achieve. Can you elaborate so that we can try to help you?

--
Scott