Configuring a NAT Environment

This is a configuration example to simulate the case of a hosted XiVO, i.e. an environment where:

  • the XiVO has a public IP address

  • the phones are behind a NAT

In this example, we’ll reproduce the following environment:


Phones behind a NAT


  • the XiVO is installed inside a virtual machine

  • the host machine is used as a router, a NAT and a DHCP server for the phones

  • the phones are in a separate VLAN than the XiVO, and when they want to interact with it, they must pass through the NAT

With this setup, we could also put some phones in the same VLAN as the XiVO. We would then have a mixed environment, where some phones are behind the NAT and some phones aren’t.

Also, it’s easy to go from a non-NAT environment to a NAT environment with this setup. What you usually have to do is only to switch your phone from the “XiVO” VLAN to the “phones” VLAN, and reconfiguring the lines on your XiVO.

The instruction in this page are written for Debian jessie and VirtualBox.


On the host machine:

  • 1 VLAN network interface for the XiVO. In our example, this will be eth0.341, with IP

  • 1 VLAN network interface for the phones. In our example, this will be eth0.342, with IP

On the guest machine, i.e. on the XiVO:

  • 1 network adapter attached to the “XiVO” VLAN network interface. In our example, this interface inside the virtual machine will have the IP


  1. On the host, install the ISC DHCP server:

    apt-get install isc-dhcp-server
  2. If you do not want it to always be started:

    systemctl disable isc-dhcp-server.service
  3. Edit the DHCP server configuration file /etc/dhcp/dhcpd.conf. We need to configure the DHCP server to serve network configuration for the phones (Aastra and Snom in this case):

    ddns-update-style none;
    default-lease-time 3600;
    max-lease-time 86400;
    log-facility daemon;
    option space Aastra6700;
    option Aastra6700.cfg-server-name code 2 = text;
    option code 3 = boolean;
    class "Aastra" {
        match if substring(option vendor-class-identifier, 0, 6) = "Aastra";
        vendor-option-space Aastra6700;
        option Aastra6700.cfg-server-name = "";
        option false;
    class "Snom" {
        match if substring(option vendor-class-identifier, 0, 4) = "snom";
        option tftp-server-name = "";
        # the domain-name-servers option must be provided for the Snom 715 to work properly
        option domain-name-servers;
    subnet netmask {
    subnet netmask {
    subnet netmask {
        option subnet-mask;
        option broadcast-address;
        option routers;
        option ntp-servers;
  4. If you have many network interfaces on your host machine, you might also want to edit /etc/default/isc-dhcp-server to only include the “phones” VLAN network interface in the “INTERFACES” variable.

  5. Start the isc-dhcp-server:

    systemctl start isc-dhcp-server.service
  6. Add an iptables rules to do NAT:

    iptables -t nat -A POSTROUTING -o eth0.341 -j MASQUERADE
  7. Make sure that IP forwarding is enabled:

    sysctl -w net.ipv4.ip_forward=1
  8. Put all the phones in the “phones” VLAN on your switch

  9. Activate the NAT and Monitoring options on the Services ‣ IPBX ‣ General settings ‣ SIP Protocol page of your XiVO.

Note that the iptables rules and the IP forwarding setting are not persistent. If you don’t make them persistent (not documented here), don’t forget to reactivate them each time you want to recreate a NAT environment.