Selective VPN routing [Solution: DSVR]

July 5, 2013 § 27 Comments

Before sharing about what I believe is my best solution yet, i’ll take a walk down memory lane…

Client VPN

Got my first VPN account (PPTP/L2TP) and happily used it from my various Windows/Mac/iOS clients. Very quickly I came across a few limitations, namely:

1) Only one device at a time could use the VPN.
2) More restricted clients did not have a client side capability to configure the VPN (like the Apple TV/PS3)
3) When a device was on the VPN, all traffic went down it – not ideal from a performance perspective, and when you’re location is determine by IP (e.g. Google Maps).
4) Minor at the time, but could not have multiple VPNs running.

Router VPN [+Source Based Routing]

Configuring  VPN connection at a single aggregation point (i.e. the router) was the next step, as this did solve some of the limitations (1 & 2 above). After a bunch of research (read: trial/error) I concluded that there was no practical way to be selective at the router based on destination as many services used over the VPN where using CDNs with massive network ranges which we’re not practically predictable.

I decided that source based routing was a good solution, in my case I selected my Apple TV to be the only source to push down the VPN this has served me well,  and I published a tutorial on it a while back.

Defining the next step

Even though my problem/use-case had largely been solved, I wanted to go further. I set myself the following goals for my next solution:

1) Selective destination routing, route only sites/domains I want.
2) Multiple concurrent VPN client support, each with their own destination mappings.
3) Multiple clients able to share the outgoing VPN(s) connection(s)
4) A ‘plug-n-play’ appliance, with no configuration changes to exiting infrastructure (clients/router/modem)
5) Simple web administration interface.

With those goals in mind – it was time to determine a solution.

New Solution: DSVR [Domain-Specific VPN Router]

dsvr-logical-v0.2

1. Selective destination routing

I’ve already touched on some of the challenges (e.g CDNs) – there were a few more – but ultimately I determined that a pre-populated list of IP routes for a service will not work.

Then an idea came to me – what if I made something that I’d best describe as a ‘DNS Router’, at a high-level it would need to do the following:

1) Intercept all outgoing DNS queries from my clients.
2) Analysis the query name against which domains I’m interested in pushing down the VPN.
3) Pass the unmodified DNS request upstream to a valid DNS server, and get a valid response back.
4) Before passing the DNS response to the original client, add routes for the RR data within the DNS record

What does this do? For each matched DNS request we are creating static routes down the VPN!

Theory is great – but I needed to now make this thing.

It was clear to me that the best starting point was to leverage existing work that’s been done creating a DNS proxy. I found a great one – dnschef – by Peter Kacherginsky. Using this as a strong foundation I was able to modify and expand this to perform the 4 points above, and also handle some edge cases around CNAME responses etc.

In my testing – this has proven to work and be stable.

2. ‘Plug-n-play’ appliance, no configuration changes, clients able to share

Deciding on a hardware platform for the appliance was easy – Raspberry Pi – it’s low-cost, low-power, runs linux and small. It’s not without it’s limitations though (e.g. NIC limited by USB bus)

The aggregation point I selected to place the Raspberry Pi was between the existing CE/Modem and home router. This meant the RPi had to be configured as a typical NAT router. Other than the OS level configuration required to create the router, the RPi only has a single NIC, so I added a second NIC interface using a USB add-on.

To achieve the second portion of this goal ‘no configuration changes to exiting infrastructure’, I used iptables to transparent redirect all outbound DNS queries to my new custom DNS proxy/router.

dsvr-physical-v0.2

3. Concurrent VPN client support

This was wasn’t too tough (for PPTP), basically just needed to configure the following for each:

1) PPP peer file
2) IP-UP script
3) INIT.D script

OpenVPN support is in the pipeline.

4. Web administration

Seeing that the core capability was done in Python, it was a logical choice to create the web interface in the same. I selected the Flask web-framework, and I used there small dev web server in lieu of the big boys like Apache.

The web interface allows for the following functions:

1) PPTP VPNs – Add/Modify/Delete
2) Specify which wildcard domains should route down which VPN
3) Stop/Start/Restart the core DSVR service
4) Status display for PPTP tunnel status, IP assignments, Route counts, uptime, mem/cpu usage
5) Reboot the RPi

webadmin (1)

Get/Build it

This blog post is just a static introduction. The code, instructions, limitations, issues and TODO’s are being maintained on the DSVR github page.

Do note that this should be considered an ALPHA release – it has not been tested by many people – use at your own risk.

gitHub-download-button

StrongVPN PPTP on DD-WRT – Source based routing (improved)

November 16, 2011 § 21 Comments

Update: Suggest you consider a new solution, that I’ve posted here

Hi there –

Myself and others have had a problem using the solution that I posted here. It works for a couple of hours, but then stops and requires a reboot to get it running again. I finally took some time to try and figure it out, and found that I needed to modify the IP-UP script to reestablish a couple of things. Here is an update to the original post:

I’m a StrongVPN customer and just today I had a use case that required that I was able to setup the VPN tunnel from my router and only route a specific host down the VPN.

Here is how I did it using these:

Do the following on your router:

Services->VPN

  • PPTP Client Options: Enable
  • Server IP or DNS name: <this is the IP of the VPN server, hostnames DON’T work>
  • Remote Subnet: <This is the IP that the YOU receive from the VPN server, to get this first connect on Mac/Win and check what IP you get)
  • Remote Subnet Mask: <This is the Subnet Mask of the remote VPN server, to get this first connect on Mac/Win and check what subnet you get – likely that 255.255.255.0 would be fine>
  • MPPE Encryption: mppe required,stateless
  • MTU: 1450
  • MRU: 1450
  • NAT: Enable
  • Username: <This is your StrongVPN user ID>
  • Password: <This is your StrongVPN password>

Setup -> Basic Setup

Under: Network Address Server Settings (DHCP)

  • Static DNS 1: 216.131.94.5
  • Static DNS 2: 216.131.95.20

Administration -> Commands

  • EDIT the INT and SOURCETOROUTE and interface (e.g ppp0) to suit and paste the following to the end of the STARTUP script, then click ‘save startup’. The IP specified in SOURCETOROUTE is the source IP that will be routed via the VPN.
    # Customize PPTPD client
    sleep 50
    mkdir /tmp/etc/config
    echo "#!/bin/sh" > /tmp/pptpd_client/ip-up;
    echo "SOURCETOROUTE=192.168.1.119" >> /tmp/pptpd_client/ip-up;
    echo "REMOTEIP=\$(ifconfig ppp0 | sed -n 's/.*inet *addr:\([0-9\.]*\).*/\1/p')" >> /tmp/pptpd_client/ip-up;
    #echo "ip rule add from \$SOURCETOROUTE table 200" >> /tmp/pptpd_client/ip-up;
    echo "/usr/sbin/ip route add default via \$REMOTEIP dev ppp0 table 200" >> /tmp/pptpd_client/ip-up;
    echo "/usr/sbin/ip route flush cache" >> /tmp/pptpd_client/ip-up;
    echo "touch /tmp/execute-debug" >> /tmp/pptpd_client/ip-up;
    echo "/usr/sbin/iptables --table nat --append POSTROUTING --out-interface ppp0 --jump MASQUERADE" >> /tmp/pptpd_client/ip-up;
    echo "/usr/sbin/iptables --insert FORWARD --protocol tcp --tcp-flags SYN,RST SYN --jump TCPMSS --clamp-mss-to-pmtu" >> /tmp/pptpd_client/ip-up;
    #echo "echo "/tmp/pptpd_client/ip-up - $(date)" >> /tmp/dbvpndebug" >> /tmp/pptpd_client/ip-up;
    chmod 777 /tmp/pptpd_client/ip-up;
    
  • Then in the same area, add the following to the FIREWALL script, and once again modify the SOURCETOROUTE and interface as necessary:
    INT=ppp0
    SOURCETOROUTE=192.168.1.119
    echo “sleep 40″ > /tmp/firewall_script.sh
    echo “/usr/sbin/iptables –table nat –append POSTROUTING –out-interface $INT –jump MASQUERADE” >> /tmp/firewall_script.sh ;
    echo “/usr/sbin/iptables –insert FORWARD –protocol tcp –tcp-flags SYN,RST SYN –jump TCPMSS –clamp-mss-to-pmtu” >> /tmp/firewall_script.sh ;
    echo “ip rule add from $SOURCETOROUTE table 200″ >> /tmp/firewall_script.sh ;
    echo “REMOTEIP=\$(ifconfig ppp0 | sed -n ‘s/.*inet *addr:\([0-9\.]*\).*/\1/p’)” >> /tmp/firewall_script.sh ;
    echo “/usr/sbin/ip route add default via \$REMOTEIP dev ppp0 table 200″ >> /tmp/firewall_script.sh ;
    #echo “echo “/tmp/firewall_script.sh – $(date)” >> /tmp/dbvpndebug” >> /tmp/firewall_script.sh ;
    sh /tmp/firewall_script.sh &
    

    Enjoy.

StrongVPN PPTP on DD-WRT – Source based routing

May 16, 2011 § 15 Comments

Update: Improved version posted here

I’m a StrongVPN customer and just today I had a use case that required that I was able to setup the VPN tunnel from my router and only route a specific host down the VPN.

Here is how I did it using these:

Do the following on your router:

Services->VPN

  • PPTP Client Options: Enable
  • Server IP or DNS name: <this is the IP of the VPN server, hostnames DON’T work>
  • Remote Subnet: <This is the IP that the YOU receive from the VPN server, to get this first connect on Mac/Win and check what IP you get)
  • Remote Subnet Mask: 255.255.255.0
  • MPPE Encryption: mppe required,stateless
  • MTU: 1450
  • MRU: 1450
  • NAT: Enable
  • Username: <This is your StrongVPN user ID>
  • Password: <This is your StrongVPN password>

Setup -> Basic Setup

Under: Network Address Server Settings (DHCP)

  • Static DNS 1: 216.131.94.5
  • Static DNS 2: 216.131.95.20

Security -> Firewall

  • SPI Firewall: Disable

Administration -> Commands

  • EDIT the INT and SOURCETOROUTE variables to suite and paste the following, then click ‘save firewall’. The IP specified in SOURCETOROUTE is the source IP that will be routed via the VPN.
    INT=ppp0
    SOURCETOROUTE=192.168.1.119
    echo "sleep 40" &gt; /tmp/firewall_script.sh
    echo "/usr/sbin/iptables --table nat --append POSTROUTING --out-interface $INT --jump MASQUERADE" &gt;&gt;  /tmp/firewall_script.sh ;
    echo "/usr/sbin/iptables --insert FORWARD --protocol tcp --tcp-flags SYN,RST SYN --jump TCPMSS --clamp-mss-to-pmtu" &gt;&gt; /tmp/firewall_script.sh ;
    echo "ip rule add from $SOURCETOROUTE table 200" &gt;&gt; /tmp/firewall_script.sh ;
    echo "REMOTEIP=\$(ifconfig $INT | sed -n 's/.*inet *addr:\([0-9\.]*\).*/\1/p')"  &gt;&gt; /tmp/firewall_script.sh ;
    echo "ip route add default via \$REMOTEIP dev $INT table 200"  &gt;&gt; /tmp/firewall_script.sh ;
    echo "ip route flush cache" &gt;&gt;  /tmp/firewall_script.sh ;
    sh /tmp/firewall_script.sh &amp;
    
  • Reboot your router, after which give it about 5mins and give it a try from the machine specified in SOURCETOROUTE

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