How can I create a VM in virt-manager that can access the internet through the host but can't even see the host or other devices on the LAN?
10:49 p.m.
I want to be able to create multiple VMs for testing purposes -- questionable websites,
files that could be infected with a virus, etc.
I want to make sure these VMs should be able to access the internet (through the host) but
they should not be able to access the host or any other device on the LAN.
I tried `NAT` mode but that let's me access the host and other devices on the LAN.
I tried `Isolated` mode but that doesn't give me internet access.
I don't want to run a second VM and route traffic through it.
I want to avoid creating FW rules on the host or VMs because I'll be creating and
destroying VMs all the time.
And I think I need to use some kind of NAT because I don't want my router to know/see
the VMs as clients.
What do I need to do?
12:10 a.m.
New subject: How can I create a VM in virt-manager that can access the
internet through the host but can't even see the host or other devices on the LAN?
I want to make sure these VMs should be able to access the internet
(through the host) but they should not be able to access the host or any
other device on the LAN.
The first and simplest solution comes into my mind is to use the direct
type interface (aka. macvtap).
<interface type='direct'>
<source dev='eth0' mode='private'/>
</interface>
Note: "eth0" is the active interface on the host, with internet connection.
With macvtap, your VM will be in the same subnet as the host. If there is a
dhcp server in this subnet, the VM will get a dhcp address.
With mode as "private", it can not access the endpoints (other VMs with the
same setting: direct + eth0 + private).
The VM will have the same internet connectivity as its host, but the VM and
host can not access each other.
But other devices on the same LAN *can* access the VM and vice versa (like
other hosts in the same subnet as the host). Maybe you can use firewalld
rules to fine tune it.
And I wonder if we block the connection from the VM to all the hosts in the
same subnet, how can it access the internet as it can not access the
default gateway?
Another solution is to use virtual network with forward mode as "open".
With this mode, libvirt will not add any rules, so users can customize how
it works by their needs, this may be more complicated.
Hope it helps.
BR,
Yalan
On Fri, May 17, 2024 at 11:50 AM <imthenachoman(a)gmail.com> wrote:
> I want to be able to create multiple VMs for testing purposes --
> questionable websites, files that could be infected with a virus, etc.
>
I want to make sure these VMs should be able to access the internet
(through the host) but they should not be able to access the host or any
other device on the LAN.
>
> I tried `NAT` mode but that let's me access the host and other devices on
> the LAN.
>
> I tried `Isolated` mode but that doesn't give me internet access.
>
> I don't want to run a second VM and route traffic through it.
>
> I want to avoid creating FW rules on the host or VMs because I'll be
> creating and destroying VMs all the time.
>
> And I think I need to use some kind of NAT because I don't want my router
> to know/see the VMs as clients.
>
> What do I need to do?
>
>
7:21 a.m.
New subject: How can I create a VM in virt-manager that can access the internet
through the host but can't even see the host or other devices on the LAN?
I don't have a router that I can create custom rules to block things. I was hoping
there would be a way to do this entirely on the host but it doesn't look like it is
possible.
8:37 a.m.
New subject: How can I create a VM in virt-manager that can access the
internet through the host but can't even see the host or other devices on the
LAN?
I think such a thing can be done with macvtap. Check about using different vlans and test
macvtap modes that prevent communicating with the host.
I don't have a router that I can create custom rules to block things. I
was hoping there would be a way to do this entirely on the host but it
doesn't look like it is possible.
12:53 p.m.
New subject: How can I create a VM in virt-manager that can access the internet
through the host but can't even see the host or other devices on the LAN?
I don't have a VLAN aware router. Or do you mean create VLANs on the host? I'm not
even sure how to do that.
10:16 a.m.
New subject: How can I create a VM in virt-manager that can access the
internet through the host but can't even see the host or other devices on the
LAN?
On 5/17/24 14:21, Anchal Nigam wrote:
I don't have a router that I can create custom rules to block
things. I was hoping there would be a way to do this entirely on the host but it
doesn't look like it is possible.
macvtap IS purely host thing. No need to set anything on the router. In
fact, you'd need a special switch if you wanted two guests using macvtap
on the same host to talk to each other (it's called hairpinning).
Michal
10:50 a.m.
New subject: How can I create a VM in virt-manager that can access the
internet through the host but can't even see the host or other devices on the LAN?
On Fri, May 17, 2024 at 11:25 AM Michal Prívozník <mprivozn(a)redhat.com> wrote:
On 5/17/24 14:21, Anchal Nigam wrote:
> I don't have a router that I can create custom rules to block things. I was
hoping there would be a way to do this entirely on the host but it doesn't look like
it is possible.
>
macvtap IS purely host thing. No need to set anything on the router. In
fact, you'd need a special switch if you wanted two guests using macvtap
on the same host to talk to each other (it's called hairpinning).
Michal
If it was my setup I would
- Create an internal network for these test guests
- Connect the network to the router using a vlan or a specific
network/30 with a route definition on the vm server. Ideally you could
then say in said router that any traffic coming from network/30 goes
straight outside.
12:57 p.m.
New subject: How can I create a VM in virt-manager that can access the internet
through the host but can't even see the host or other devices on the LAN?
But to use VLANs I would create them on my router, right?
Cause I need to block the VM from accessing the host or any other device on my
network/LAN.
8:47 a.m.
New subject: How can I create a VM in virt-manager that can access the
internet through the host but can't even see the host or other devices on the LAN?
On Fri, May 17, 2024 at 2:20 PM Anchal Nigam <imthenachoman(a)gmail.com> wrote:
But to use VLANs I would create them on my router, right?
Cause I need to block the VM from accessing the host or any other device on my
network/LAN.
1. I said vlan OR network
2. Don't want to touch router? Fine! Find a vpn that plays nice with
openvpn. Setup your guest network to go out through vpn. profit. Be
mindful of what comes out of your guests as vpn provider may shut you
down.
10:17 a.m.
New subject: How can I create a VM in virt-manager that can access the
internet through the host but can't even see the host or other devices on the
LAN?
On 5/17/24 11:16 AM, Michal Prívozník wrote:
On 5/17/24 14:21, Anchal Nigam wrote:
> I don't have a router that I can create custom rules to block things. I was
hoping there would be a way to do this entirely on the host but it doesn't look like
it is possible.
>
macvtap IS purely host thing. No need to set anything on the router. In
fact, you'd need a special switch if you wanted two guests using macvtap
on the same host to talk to each other (it's called hairpinning).
More specifially, if the macvtap interface (type='direct' in the libvirt
domain XML) has
<source dev='ethX' mode='private'/>
*then* that guest can only communicate with other guests connected via
dev='ethX' if the traffic is hair-pinned back from the bridge that
connects device 'ethX' to the physical network. But if it is
<source dev='ethX' mode='bridge'/>
then that guest *can* communicate with all other guests connected to
ethX. In both cases, the guests cannot communicate with the host.
But even mode='private' doesn't provide the level of isolation that's
being requested. You might think you could combine macvtap/private with
a few iptables/nftables rules on the host that reject any forwarded
traffic that has source or destination on the local network, but none of
the iptables hooks works with traffic on a macvtap interface. It *is*
apparently possible (although I've not tried it) to do nftables
filtering of traffic on a macvtap interface by using the "netdev"
ingress and egress hooks, as outlined here:
https://serverfault.com/questions/1147529/applying-nftables-rules-to-macv...
(it even gives an example of implementing this in a libvirt hook script,
which would be necessary for you to use it with a libvirt-created
macvtap interface).
An alternate implementation managed entirely on the host, would be to
connect the guest via a libvirt network in nat/bridge/open forward mode
(to ensure that a regular tap device is used) and then use libvirt's
nwfilter to create a filter that rejects all traffic to the local
network, but allows everything else. Basic information about libvirt's
nwfilter driver is here:
https://libvirt.org/formatnwfilter.html
10:45 a.m.
New subject: How can I create a VM in virt-manager that can access the internet
through the host but can't even see the host or other devices on the LAN?
This is helpful. Thank you!
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10 comments
7 participants
participants (7)
-
Anchal Nigam -
imthenachoman＠gmail.com
-
Laine Stump -
Marc -
Mauricio Tavares -
Michal Prívozník -
Yalan Zhang