---
title: "Transparently Proxying VMs"
menu:
    howto:
        weight: 3
---

# Transparently proxify virtual machines

This walkthrough illustrates how to set up transparent proxying with
mitmproxy. We use VirtualBox VMs with an Ubuntu proxy machine in this
example, but the general *Internet \<--\> Proxy VM \<--\> (Virtual)
Internal Network* setup can be applied to other setups.

## 1. Configure Proxy VM

On the proxy machine, **eth0** is connected to the internet. **eth1** is
connected to the internal network that will be proxified and configured
to use a static ip (192.168.3.1).

### VirtualBox configuration


{{< figure src="/transparent-vms/step1_vbox_eth0.png" >}}

{{< figure src="/transparent-vms/step1_vbox_eth1.png" >}}


### VM Network Configuration

{{< figure src="/transparent-vms/step1_proxy.png" >}}

## 2. Configure DHCP and DNS

We use dnsmasq to provide DHCP and DNS in our internal network. Dnsmasq is a
lightweight server designed to provide DNS (and optionally DHCP and TFTP)
services to a small-scale network. Before we get to that, we need to fix some
Ubuntu quirks: **Ubuntu \>12.04** runs an internal dnsmasq instance (listening
on loopback only) by default
[\[1\]](https://www.stgraber.org/2012/02/24/dns-in-ubuntu-12-04/). For our use
case, this needs to be disabled by changing `dns=dnsmasq` to `#dns=dnsmasq` in
**/etc/NetworkManager/NetworkManager.conf** and if on Ubuntu 16.04 or newer
running:

{{< highlight bash  >}}
sudo systemctl restart NetworkManager
{{< / highlight >}}

If on Ubuntu 12.04 or 14.04 running:

{{< highlight bash  >}}
sudo restart network-manager
{{< / highlight >}}

afterwards.

Now, dnsmasq can be be installed and configured:

{{< highlight bash  >}}
sudo apt-get install dnsmasq
{{< / highlight >}}

Replace **/etc/dnsmasq.conf** with the following configuration:

{{< highlight none  >}}
# Listen for DNS requests on the internal network
interface=eth1
# Act as a DHCP server, assign IP addresses to clients
dhcp-range=192.168.3.10,192.168.3.100,96h
# Broadcast gateway and dns server information
dhcp-option=option:router,192.168.3.1
dhcp-option=option:dns-server,192.168.3.1
{{< / highlight >}}

Apply changes:

If on Ubuntu 16.04 or newer:

{{< highlight bash  >}}
sudo systemctl restart dnsmasq
{{< / highlight >}}

If on Ubuntu 12.04 or 14.04:

{{< highlight bash  >}}
sudo service dnsmasq restart
{{< / highlight >}}

Your **proxied machine** in the internal virtual network should now receive an
IP address via DHCP:

{{< figure src="/transparent-vms/step2_proxied_vm.png" >}}

## 3. Redirect traffic to mitmproxy

To redirect traffic to mitmproxy, we need to add two iptables
rules:

{{< highlight bash  >}}
sudo iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 80 -j REDIRECT --to-port 8080
sudo iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 443 -j REDIRECT --to-port 8080
{{< / highlight >}}

## 4. Run mitmproxy

Finally, we can run mitmproxy in transparent mode with

{{< highlight bash  >}}
mitmproxy -T
{{< / highlight >}}

The proxied machine cannot to leak any data outside of HTTP or DNS requests. If
required, you can now [install the mitmproxy certificates on the proxied
machine]({{< relref "concepts-certificates" >}}).
