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I have currently a Xen on a debian wheezy dom0. I have 6 (public) ips and I would like to setup 6 VMs (each using one IP).

To keep access to dom0, I'd like dom0 ssh to bind on one IP port (lets say 4444). I don't really know where to start. Any pointers ?

  • 1
    It's best if you get seven IP addresses here. – Michael Hampton Feb 1 '14 at 16:10
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    Sure, but I would like to stick with 6. – NoWiS Feb 1 '14 at 16:14
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So, I finally came up with a solution that I will details :

In this exemple, we have one physical network interface (eth0), 3 IPs and 3 VMs :

  • a.a.a.a (that will be shared by dom0 and one domU called VM_A)
  • b.b.b.b (for one domU VM_B)
  • b.b.b.c (for one domU VM_C)

dom0 /etc/network/interface:

auto xenbr0 
iface xenbr0 inet static
    bridge_ports eth0
    address a.a.a.a
    netmask 255.255.255.0
    network a.a.a.0
    broadcast a.a.a.255
    gateway a.a.a.254

The default vif script used in /etc/xen/xend-config.sx will be (vif-script vif-bridge). This is for VM_B and VM_C which have their own ip.

For the configuration script of VM_B and VM_C (/etc/xen/VM_[BC].cfg) we will have :

vif = [ 'ip=b.b.b.b,mac=XX:XX:XX:XX:XX:XX' ]

For the configuration script of VM_A (/etc/xen/VM_A.cfg) we will have :

vif = [ 'ip=192.168.0.1,script=vif-nat']

We have to add iptables rules in order to make VM_A visible to Internet :

iptables -t nat -A POSTROUTING -s 192.168.0.1 -o xenbr0  -j MASQUERADE
# One rule for each port that need to be forwarded to `VM_A`
iptables -t nat -A PREROUTING -p tcp -d a.a.a.a --dport 22 -j DNAT --to 192.168.0.1:22
iptables -t nat -A PREROUTING -p tcp -d a.a.a.a --dport 80 -j DNAT --to 192.168.0.1:80

Also need to enable packet forwarding (/etc/sysctl.conf):

net.ipv4.ip_forward=1
net.ipv4.conf.eth0.proxy_arp=1

And finally here is how the /etc/network/interfaces of VM_A looks like :

 # The loopback network interface
 auto lo
 iface lo inet loopback

 # 'Fake' loopback interfaces (was needed in my case for some applications)
 auto lo:1
 iface lo:1 inet static
  address a.a.a.a
  netmask 255.255.255.255

 # The primary network interface
 auto eth0
 iface eth0 inet static
  address 192.168.0.1
  gateway 192.168.0.128
  netmask 255.255.255.0

The gateway address 192.168.0.128 is selected by the vif_script by adding 127 to the given address.

And a last thing for the communication between VM_A and the other VMs (however, don't ask me why...):

echo 0 > /proc/sys/net/bridge/bridge-nf-call-iptables
  • thanks for an excellent walk-thorugh! could you please what this line does: net.ipv4.conf.eth0.proxy_arp=1 – darwin Jun 24 '15 at 15:34
  • and could you please post the config of /etc/network/interfaces in VM_A? – darwin Jun 24 '15 at 16:36
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    I added the /etc/network/interfaces of VM_A. For the arp_proxy, I think it is for the bridged IPs, not quite sure though. – NoWiS Jun 25 '15 at 13:06

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