CentOS virt - Mar 2012 - routing problem with domU bridged to two networks

As I received no response on the general CentOS list, I'll repost it
here as the question is about Xen virtual machine routing.


This is my network setup:
http://pastebin.com/kyWpTQYU


Lets assume my dom0's eth2 public ip is 1.2.3.33 and my dmz network
11.22.33.96/255.255.255.224 . I have created NAT from my LAN with
iptables. You can see my /etc/sysconfig/iptables here:
http://pastebin.com/1FqSTvPH


And this is my dom0 routing table:
http://pastebin.com/gNjTFHp5


My goal:

To access NFS shares on a (non-virtualized) file server in the LAN
network from the domU web server in the DMZ network.


What I tried:

I attached the domU to both bridges using this Xen config:

vif = [
"mac=00:0c:29:de:3a:fe,bridge=xenbr0","mac=00:0C:29:76:19:85,bridge=xenbr1"
]

and then created two eth interfaces inside the domU mapping to the MAC
addresses above, giving eth1 an IP from the DMZ (11.22.33.111) and
giving eth2 an IP from the LAN (192.168.0.12). After this I mounted
the NFS share from the file server (192.168.0.2).


My problem:

If my domU web server is connected to both LAN and DMZ using the two
bridges xenbr0 and xenbr1, I can access the NFS share from the domU
web server and everything else works as expected, except for one thing
-- my workstations in the LAN cannot anymore access the web server:
web pages do not open anymore and from the workstations I cannot ping
the domU. If the web server domU is only connected to DMZ via xenbr0,
the workstations can access it ok.


Any advice what I am doing wrong and I could fix my setup?


Regards,
Peter

On Wed, 2012-03-07 at 20:41 +0200, Peter Peltonen wrote:
> As I received no response on the general CentOS list, I'll repost it
> here as the question is about Xen virtual machine routing.
> 
> 
> This is my network setup:
> http://pastebin.com/kyWpTQYU
> 
> 
> Lets assume my dom0's eth2 public ip is 1.2.3.33 and my dmz network
> 11.22.33.96/255.255.255.224 . I have created NAT from my LAN with
> iptables. You can see my /etc/sysconfig/iptables here:
> http://pastebin.com/1FqSTvPH
> 
> 
> And this is my dom0 routing table:
> http://pastebin.com/gNjTFHp5
> 
> 
> My goal:
> 
> To access NFS shares on a (non-virtualized) file server in the LAN
> network from the domU web server in the DMZ network.
> 
> 
> What I tried:
> 
> I attached the domU to both bridges using this Xen config:
> 
> vif = [
"mac=00:0c:29:de:3a:fe,bridge=xenbr0","mac=00:0C:29:76:19:85,bridge=xenbr1"
> ]
> 
> and then created two eth interfaces inside the domU mapping to the MAC
> addresses above, giving eth1 an IP from the DMZ (11.22.33.111) and
> giving eth2 an IP from the LAN (192.168.0.12). After this I mounted
> the NFS share from the file server (192.168.0.2).
> 
> 
> My problem:
> 
> If my domU web server is connected to both LAN and DMZ using the two
> bridges xenbr0 and xenbr1, I can access the NFS share from the domU
> web server and everything else works as expected, except for one thing
> -- my workstations in the LAN cannot anymore access the web server:
> web pages do not open anymore and from the workstations I cannot ping
> the domU. If the web server domU is only connected to DMZ via xenbr0,
> the workstations can access it ok.
> 
> 
> Any advice what I am doing wrong and I could fix my setup?
  The postrouting command uses -o eth2.  To NAT LAN requests to your DMZ
web server, shouldn't you be using xenbr0?

  Though, I would bridge eth2, as well, and create a virtual firewall
with eth0 (DMZ?), eth1 (LAN) and eth2 (PUB).  I wouldn't want the Dom0
to be directly compromised if my firewall was compromised.
> Regards,
> Peter
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