KVM Virtual Machine Network - Guest-guest/VM-VM only network (no host/hypervisor access, no outbound connectivity)

[Laine Stump]

On 6/11/21 7:22 PM, Eduardo Lúcio Amorim Costa wrote:
> I know that with the *virsh* command I can create several types of 
> networks (a "NAT network", for example) as we can see in these URLs...
> 
> KVM network management <https://programmersought.com/article/52213715009/>
> KVM default NAT-based networking 
> <https://www.ibm.com/downloads/cas/ZVJGQX8E> (page 33)
> 
> *QUESTION:* How can I create a network (*lan_n*) where only guests/VMs 
> have connectivity, with no outbound connectivity and no host/hypervisor 
> connectivity?

(Just to be sure I'm understanding correctly - you want the guests on 
this network to have connectivity to each other, but not guest<->host, 
and nothing beyond the host, correct?)

Normally the guests would get their DHCP-assigned IP address from the 
host, and use the host for DNS, but since you want to forbid 
guest<->host communication, that implies that either one of the guests 
on the network will act as DHCP/DNS server, or that the guests will have 
statically configured IP addresses.

That being the case, all you really need is to define a libvirt virtual 
network that has no IP address on the host, e.g.:

    <network>
      <name>super-isolated</name>
    </network>

(It *might* be necessary to add "ipv6='yes'" immediately after "network" 
in order for IPv6 connectivity to work, but I'm not sure  and don't have 
a setup to try it right now).

> 
> *NOTE:* The connectivity to other resources will be provided by a 
> *pfSense* firewall server that will have access to another network 
> (*wan_n*) with outbound connectivity and other resources.

Yes, this is a common config - have a "super-isolated" network for all 
the guests + the firewall VM, and then the firewall VM has a 2nd 
interface that connects everyone to the outside.

> 
> |Network layout... [N]wan_n ↕ [I]wan_n [V]pfsense_vm [I]lan_n ↕ [N]lan_n 
> ↕ ............................. ↕ ↕ ↕ [V]some_vm_0 [V]some_vm_1 
> [V]some_vm_4 [V]some_vm_2 [V]some_vm_5 [V]some_vm_3 _ [N] - Network; _ 
> [I] - Network Interface; _ [V] - Virtual Machine. |

Sigh. Stupid email client formatting - your original ASCII diagram 
looked nice, but just look at what Thunderbird did to it when I hit 
reply :-/ (fortunately I didn't need to refer to it)