Connecting 2 virtual machines to a single network

[Taigo]

For school i have to connect 2 virtual machines to a single network yet giving one machine internet using NAT. My school assumes i use VMware on MS Windows... but it doesn't work that well so i use kvm/qemu instead. I have been googling a lot about it but i don't understand a lot about it. Networking really is my weak spot.

[Christian99]

qemu is quite manual, it has some guis, but I never used them...

Personally, I do use Virtualbox, this has a nice gui, where you can setup this network stuff quite easily, maybe you want to give that a try?
If yes, and you still need advice with the network settings, don't hesitate to come back.

[alamahant]

Kvm by default uses NAT networking.
You need qemu, libvirt and virt-manager.
So if you just create 2 vms they will --by default be on the same NAT network.
What exactly is your assignment?
Create two vms in two different NAT networks and being able to ping each other?
Can you plz be a bit more specific?
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[Taigo]

[szatox]

"single domain" sounds more like they should be connected with a bridge, so they can actually see each other.
Unless there are other restrictions. in the task.

You can add an IP address to the bridge to let the guests talk to the host, and NAT rules (with iptables MASQUERADE target) on top of that to let those machines connect to the internet.

[Taigo]

My teacher told me not to use bridges (no idea myself about those). i forgot to mention that sever 1 should get internet from the host and server 2 should get internet from server 1.

[NeddySeagoon]

Taigo,

If you set up a KVM with virt-manager, thats the GUI, your KVM will get an IP in the the 192.168.122.0/24 range for free.
It will also get NAT to the internet too. So that's VM 1.

If you turn off NAT when you make VM 2, it will only have an IP in the 192.168.122.0/24 range, so it can connect to VM 1 but not to the internet yet.

How you make VM 1 share its internet connection is up to you.

You can have a fully fledged router/firewall on VM 1. You should add another network card to VM1 for that.
For one other host, you can run PPP over another interface.
You can also just set up IP forwarding in VM 1. That may be free with NAT, so if you set a default route in VM 2 to point to VM 1, it may just work.

What is it you are supposed to learn from this exercise?
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

[Taigo]

Oh could it be a problem that I changed the IP to be 192.168.1.X on both VM's? My school doesn't really do seperate exercises but it's more, you set up a server and you keep adding features and certain things to it and learn about it that way. I'm supposed to learn how to make routers out of the servers, make a active directory and add other servers to that. i think you are right because I do recall my teacher saying I would need 2 network cards on my first vm and a single one on the second being connected to the first server.

[NeddySeagoon]

Taigo,

The default DHCP settings provided by thu virt-manager is to have the gateway at 192.168.122.1 and the rest of the 192.168.122.0/24 subnet available for VMs.
They will all use 192.168.122.1 for NAT.

Feel free to change everything but you have to change all the bits together, or it won't work.

It sounds like you are expected to set up a router.
Not to give the game away entirely., there are several guides on the wiki for that.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

[alamahant]

If the 2 VM are assigned a bridged adapter they will share the host LAN and be able to talk to each other the host and the outer internet.
If they are created in two separate LANs ie you assign them different NAT ifaces then both will be able to talk to the internet but NOT each other.To enable intra lan communication you need to add 6 iptables rules on the host.
A third case they both reside in the same network ,be it the host LAN or some NAT network but the one has connection to the internet and the second doesnt.
Which case best describes your needs?
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[szatox]

Oh, well, you clearly need a bridge to connect 2 machines (without connecting them to the internet) and an extra interface on one of them that will allow the traffic to go outside. The latter can even be in "user mode" for pretty much zero-config at the expense of performance you don't need there anyway.

[Taigo]

i guess it would work if I give vm 1 internet through NAT and connecting vm 1 with 2 using a bridge but I'm not so familiar with setting them up (which i hope google will help me) and connecting them so they act just like they would be connected to a hub/switch.

[alamahant]

[NeddySeagoon]

Taigo,

A bridge is the software equivalent of an Ethernet hub. To connect virtual machines together you connect both (or more) to the same bridge. Think of it as connecting the virtual Ethernet cables together.
The host may or may not connect to the bridge.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

[Taigo]

ahhh, thanks for that information. that sound exact like what i need. i guess o will try connecting them now.

[Taigo]

I have created virbr0 but when i add the cards to the vm and start it the bridges don't seem to have an ip. also seems like it created other devices called vnet0 vnet1 and vnet2. I went with the default settings so i could have had something i needed to do but i don't know what that would or could be.

[alamahant]

[Taigo]

[alamahant]

[Taigo]

ip a output: http://0x0.st/odhx.txt

I added the new created network and the bridge on both VMs and it looks like progress, both VMs now have 2 ethernet when running ipconfig. (thanks in advance)

[alamahant]

[NeddySeagoon]

Taigo,

Leave the defaults alone. They work and you may want to use the default network to fix things.

Make a new bridge on the host, call it br0 so you know its not being managed by virt-manager.
Add a second network card to each VM and connect it to br0.
That's the two VMs connected together.

Think of a private IP range that you don't use yet. 10.10.10.0/24 will do.
Inside each VM, on the interface connected to br0, assign static IPs from the 10.10.10.0/24 subnet.
They must be unique. say 10.10.10.a/24 and 10.10.10.b/24 you pick a and b. You must not use 0 or 255 by anything in between is good.

Ping 10.10.10.a from 10.10.10.b and vice versa is expected to work.

br0 is a bridge with two ports, so its just like an Ethernet cable joint.
Now you have a private network between the VMs and the 192.168.122.0/24 that goes between the VMs and the host with NAT.

If the ping 10.10.10.a works, remove the 192.168.122.0/24 IP address from VM2.
Now it can only connect to VM1 via the bridge. Ping should still work.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

[alamahant]

Ok plz follow @Neddy suggestion.
Its more elegant and simple than my own.
I was trying to avoid assigning 2 adapters to each VM.
But its better the way Neddy suggested.
_________________

[Taigo]

[Taigo]

update: strangely, also connecting vm 2 to the host results in both machines timing out when pinging each other.