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

Scott Lowe scott.lowe at scottlowe.org
Mon Nov 23 16:11:33 UTC 2015


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




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