Re: [Xen-users] Managed Firewall

[Jonathan Tripathy <jonnyt@xxxxxxxxxxx>]

On 13/06/10 10:02, Simon Hobson wrote:
> Jonathan Tripathy wrote:
>
> > Once I roll out my Xen VPS hosting solution, I wish to provide a 
> > "managed firewall" service to my customers. What I wish to do is to 
> > use my firewall (which will sit on the edge between the ISP WAN and 
> > my VM's LAN) to filter traffic between the WAN and the LAN VMs (this 
> > is easy), as well as filter between the VMs.
> > Now, this "firewall" will actually be a "filtering bridge" as the VMs 
> > will be using public IPs, so the firewall's WAN and LAN interfaces 
> > will be bridged together. My question is, how can I "force" all 
> > traffic from each VM host to go back out via the firewall? Is it just 
> > a matter of using iptables/ebtable in the bridge in the Dom0 to make 
> > sure that the vifs can only communicate with the physical interface 
> > (which will be connected to the firewall) ?
> For this to work, each VM must attach to a different "port" of your 
> firewall. If the firewall were a VM on the same host then you could 
> create a bridge per VM and connect them all to the firewall VM. But 
> since as I read it you are using an external box, then you would need 
> to use either a lot of real NICs, or more efficiently, use a VLAN per 
> VM and trunk them to the switch.
> If you just use one virtual switch (bridge) and connect multiple VMs 
> to it, then you are correct in saying the switch will simply forward 
> the packets directly between the VMs.
Hi Simon,

Thanks for your email.

Since I have plans for up to nearly 100 VMs on the same machine, how 
well would Xen cope with 100 bridges?
I also have another idea, so maybe you could tell me if it would work or 
not (Using physical firewall box):
Let's say I have just one bridge per Xen host. Could I use 
iptabled/ebtables to deny all inter-VM traffic? So only allow access 
from the VM to the physical NIC of the box? Then on the physical switch, 
I could put each port on a separate VLAN, but put the port that the 
firewall is connected to on all the VLANs. Then, I assume, the switch 
would send all traffic from the host ports to the firewall port, where 
the firewall could do filtering? I'm not sure if the firewall would even 
need to be VM aware..
Would that work? Or is that just a bad idea?

Thanks

Jonathan

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