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RE: [Xen-users] Managed Firewall

Dustin Henning wrote:

 >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..

Well the firewall will not have to be VM aware anyway - it just sees
traffic on VLAN ports.

As to having one bridge and VLANs, if you connect multiple VLANs to
one switch then that's the equivalent of trunking (bonding) multiple
links together and won't help.  The only other way round it I can see
is to use some fudging with /32 subnets for the clients so that they
have no concept of there being 'neighbours' on the local subnet (and
then enforce it with iptable/ebtables rules to prevent direct
host-host traffic) - but that's beyond my experience and I don't know
how well it works or what pitfalls there may be.

Primarily out of curiosity, are you assuming that the switch is not using
VLAN tagging along with trunking?  Is that even possible?  Assuming tagged
VLANs, I don't see what makes you think the switch is going to break that
boundary and send the data back.  Even if it did, the destination domU
should ignore it unless the tag was stripped by the switch.  Seems to me
like the switch would keep the VLANs separate and e firewall would have to
function as a sort of "VLAN Router," which may or may not be possible.

Well actually I'm not sure I fully understand the setup proposed - but I think it involved building a bridge per guest, a VLAN per bridge, and trunking the lot back to the firewall via a switch.

At some point, all these VLAns are going to have to be switched together - unless you futz about with /32 subnets on the clients. Once you do that, the switches will switch the packets back in the shortest manner available - and that is unlikely to be via the firewall unless that is doing all the switching.

It could work if the firewall supports that many interfaces, and you trunk all the VLANs back to it. Then you could setup intra-zone rules to control traffic between the VLANs, and hence between the guests.

I see no reason why a switch shouldn't support tagged packets over a bonded trunk. It's just a case of whether you can actually get anything useful from doing so.

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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