DNS - Justin Foell

This is part three of a three part series covering Dnsmasq’s uses regarding:

Local Development DNS
Local Area Network (LAN) DNS
Virtual Private Network (VPN) routing

IT savvy business often use a Virtual Private Network (VPN) connection to allow employees to connect to the (normally internal) work network while they’re traveling or working from home. Many VPNs (once connected) act at the default gateway for your computer. This is effectively like unplugging your computer from your local network and plugging it in at your workplace. This is probably for security reasons, and it’s certainly a simple configuration for most, as your computer is truly now on a remote network as if you were at your desk at work. But for some, this is becomes a restriction, and we’ll examine some cases and a workaround.

Continue reading →

Let’s say I’m connected to the VPN. All of my internet traffic goes through the VPN which is a thousand miles away. If I’m streaming a local radio station, that’s a long way to go out-and-back for something that is truly local. In addition, all of my local network resources are less usable because the VPN has instructed my computer to use the VPN’s DNS servers, so I can now only access them by IP.

It is possible to be connected to the VPN and still have access to local resources, and route (non-VPN) traffic though your normal gateway. Your VPN administrator might say this is poses a security risk, but s/he’ll be none the wiser if you don’t let on.

This configuration is for Dnsmasq and NetworkManager, which is used by Ubuntu & Fedora. But there’s no reason the concepts here can’t be applied to other Linux distributions and/or OSX.

VPN Gateway

Connect to your VPN per normal using NetworkManager. Once you’re connected you can probably deduce the default gateway by looking at output from running a traceroute to a known computer on the VPN (such as the nameserver – see below).

$ traceroute 10.20.0.26
traceroute to 10.20.0.26 (10.20.0.26), 30 hops max, 60 byte packets
 1  * * *
 2  10.20.44.253 (10.20.44.253)  101.294 ms  101.715 ms  102.610 ms
 3  10.20.0.26 (10.20.0.26)  100.205 ms  101.022 ms  101.486 ms

The first IP is likely the VPN’s default gateway, 10.20.44.253 in this case.

VPN Name Servers

You’ll also want to grab the name servers for your VPN. You can probably just inspect your /etc/resolv.conf file for this information:

$ cat /etc/resolv.conf
...
nameserver 10.20.0.26

Add new VPN connection

With this information at hand, disconnect from the VPN and create a new VPN connection in NetworkManager that is essentially the same as the existing one. Name the new connection something that indicates it’s custom (we’ll use this name later). In NetworkManager on the IPv4 Settings tab, set the Method to Automatic (VPN) addresses only:

Then click the Routes… button. In the Routes dialog you’ll want to put in the network information for your work, using the information you deduced using traceroute. My VPN addresses are all 10.x.x.x, and the VPN gateway is 10.20.44.253. So I added a line to the route table like this:

You can find the network address and netmask from the Private Network table on Wikipedia. The metric number should be fine at 10. Check the boxes to ignore obtained routes and to only use this network for resources contained within.

That gets you essentially halfway there, you can connect to the VPN and only requests for resources with network addresses that are part of the VPN will be routed through the VPN connection, everything else will gateway through your normal ISP. You can (and probably should) test this configuration by connecting to the VPN and ping-ing or traceroute-ing to a computer on the VPN (such as the nameserver) just to make sure the custom routing established is indeed working. Once routing is working, we need to fix the DNS as it’s kind of useless without it.

Create a NetworkManager dispatcher.d script to start Dnsmasq

In /etc/NetworkManager/dispatcher.d add a file called 05vpn:

#!/bin/sh

if [ "$2" = "vpn-up" ]; then
        CONN_NAME=`/usr/bin/nm-tool | grep VPN | sed 's/^.*\[\(.*\)\].*$/\1/'`
        if [ "$CONN_NAME" = "VPN Custom" ]; then
                /etc/init.d/dnsmasq start
        fi
fi

if [  "$2" = "vpn-down" ]; then
        /etc/init.d/dnsmasq stop
fi

Set the comparison to $CONN_NAME to the name of your new VPN connection. After saving the file, set it to be executable:

$ sudo chmod 755 /etc/NetworkManager/dispatcher.d/05vpn

The /etc/NetworkManager/dispatcher.d files are executed whenever a network interface goes up or down. The 05vpn file will start/stop Dnsmasq when the “custom” VPN connection is turned on/off.

Configure Dnsmasq for your VPN

Configuring Dnsmasq for your VPN really boils down to adding server entries for every domain that either resides on the VPN, or that you want to route through the VPN. Add a file in /etc/dnsmasq.d for your VPN DNS settings, such as /etc/dnsmasq.d/02_vpn

If your work has it’s own Top Level Domain (TLD), add a server line with the VPN DNS server IP and the TLD:

server=/tld/10.20.0.26

Similarly, if there are certain domains (like your company’s domain name) that act differently when you’re on the VPN, you’ll want to have them route through the VPN:

server=/mywork.com/10.20.0.26

That’s all there is to it. I’ve noticed some (newer) versions of NetworkManager automagically employ Dnsmasq to let you use any LAN resources, but other traffic (such as streaming music) would still go through the VPN.

Happy Hacking!

← Summary Only

This is part two of a three part series covering Dnsmasq’s uses regarding:

In my previous post I covered using Dnsmasq locally to bring some organization to local web development. Now I’d like to cover Dnsmasq’s use on a Local Area Network (LAN), you don’t need to be a developer to appreciate Dnsmasq as we kick it up a notch and spread the love across the network.

Continue reading →

Using Dnsmasq locally is nice and all, but what if you have a home network with multiple computers, each serving different purposes? You probably want them to inter-operate smoothly, and it’s nice to reference things by name rather than having to remember IP addresses.

OpenWrt & Dnsmasq

If you have a computer/server on your network that is on most of the time, this would be an appropriate candidate to run Dnsmasq on. Or, you can do it my preferred way, which is to buy a wireless router that supports OpenWrt (an open-source router firmware) – it includes Dnsmasq. If you decide to use an existing Mac or Unix box on your network to run Dnsmasq, see my first post regarding Dnsmasq installation and configuration, and read the documentation on Dnsmasq’s DHCP options.

For those that go the OpenWrt route, here are some tips on configuring Dnsmasq on OpenWrt Backfire (10.03.1 – latest stable as of 2012). Once your router has the OpenWrt firmware installed and you’ve logged into the web interface, navigate to the DHCP and DNS tab under Network:

The premise behind Dnsmasq is that it not only includes a DNS Server, it also includes a DHCP server. When DCHP is enabled, Dnsmasq will automagically create a DNS name for each computer that connects to the network, based on it’s hostname.

The Server Settings that determine the Top Level Domain (TLD) are Local server and Local domain, set to “lan” in my case. Every host that connects will get a “.lan” domain name. If you look at the list of Active Leases you can imagine each one getting a domain name like lappy64.lan (a play on Strongbad’s Lappy 486), printer.lan, mythtv.lan, etc. In fact, the “.lan” extension is not even needed, hosts can be address simply by their hostname – how easy is that?

For some stubborn devices, which do not report a hostname when asking for an IP address (see those with hostname of “?” in the Active Leases box), the Static Leases section can help out. Once the device is connected, click Add in the Static Leases box, then select the device’s MAC-Address from the list. Under Hostname, type in the name you’d like it to be referenced as, such as “printer.” Give the device a static IP address (something that’s not in the DHCP range specified on the Network > Interfaces > Lan tab – below .50 is probably safe). Save & Apply your changes – you might have to force the device to reconnect in order for it to get the new address.

If you’ve got computers/devices that report a hostname just fine but you’d still like to assign a static IP to, use the Static Leases section in the same way, but leave the hostname field blank.

← Summary Only

The Domain Name System (DNS) is arguably the best (and most used) service that the internet has spawned. Why leave all the fun Top Level Domain (TLD) stuff to ICANN & your registrar? You can have your own TLD using Dnsmasq.

This is part one of a three part series covering Dnsmasq’s uses regarding:

Continue reading →

The only prerequisites for running Dnsmasq is a Unix-based operating system (including Mac OSX). The only prerequisite for reading this article in the series is interest in doing any sort of web development locally. I’m going to cover a simple example using WordPress, but the principle is the same for any web site or service software written in any language. Basically, if your normal local development addresses look something like http://localhost/~me/bobscountrybunker/ then Dnsmasq is for you.

Installing & Starting Dnsmasq

I’m going to cover installation & configuration for Ubuntu 12.04, but over time I haven’t seen a lot of changes in the way Dnsmasq is configured. So configuration should apply to OSX and other Linux distros.

To install on a Debian-based system:

$ sudo apt-get install dnsmasq

Dnsmasq will probably start automatically the next time you boot, but to start it now execute:

$ sudo service dnsmasq start

Systems that don’t use upstart will probably start it like this

$ sudo /etc/init.d/dnsmasq start

Even with no configuration changes, your computer still should work as normal, but if you inspect your /etc/resolv.conf it probably now has a line like this:

nameserver 127.0.0.1

Dnsmasq is already up and running, taking in DNS requests from your computer and at this point just forwarding most of them to your upstream DNS provider. Nothing groundbreaking, but now we can control DNS ourselves and have a little fun.

Configuring Dnsmasq

The configuration files will be in /etc/dnsmasq.conf and/or /etc/dnsmasq.d. The addition of the /etc/dnsmasq.d directory is new to Ubuntu 12.04 (not sure which Dnsmasq version it corresponds to), and it’s a welcome addition because you can put your customized files in there without worrying about /etc/dnsmasq.conf getting overwritten during the next release upgrade.

The files in /etc/dnsmasq.d are executed by the order of their filename, so it would be wise to number your most important configuration with a `01` prefix, such as /etc/dnsmasq.d/01_localhost

Top Level Domains – not just for the big-boys (anymore)

You can invent a new Top Level Domain for use on your local system. On some distributions the convention is to use ‘.lan’ but you could name it what ever you’d like. I don’t recommend anything too long or the ‘.local’ extension which is used by multicast dns. Here’s a simple /etc/dnsmasq.d/01_localhost configuration file:

address=/lan/127.0.0.1

Now every address that ends in ‘.lan’ will belong to your local IP. After (re)starting Dnsmasq, try it out:

$ ping wordpress.lan
PING wordpress.lan (127.0.0.1) 56(84) bytes of data.
64 bytes from localhost (127.0.0.1): icmp_req=1 ttl=64 time=0.021 ms

Pairing Dnsmasq & Apache Web Server

Now let’s combine this with some Apache configuration for a real-world development example. I don’t want to get into the specifics of Apache configurations amongst different OSes and distributions, but on Ubuntu I put a config file in /etc/apache2/sites-available and symlink it to /etc/apache2/sites-enabled, however it can really go anywhere that Apache will read it:

<VirtualHost *:80>
    ServerName wordpress.lan
    ServerAlias *.wordpress.lan

    DocumentRoot /home/justin/wordpress
    <Directory /home/justin/wordpress/>
        Options Indexes FollowSymLinks MultiViews
        AllowOverride All
        Order allow,deny
        allow from all
    </Directory>
</VirtualHost>

Once I’ve restarted/reloaded Apache, I can visit http://wordpress.lan in my browser on my local system to bring up an instance of WordPress. You may have noticed the ServerAlias *.wordpress.lan line in the configuration. With mod_rewrite enabled in Apache, I can take the set up a step further and turn this single WordPress installation into a subdomain network installation. This is a great set up if you are working on several sites but want to maintain a single main codebase for your content management software.

← Summary Only

Justin Foell

Technology, Bicycling, Hobbies, Kids, Life.

Category Archives: DNS

(Re)routing VPN traffic with Dnsmasq

VPN Gateway

VPN Name Servers

Add new VPN connection

Create a NetworkManager dispatcher.d script to start Dnsmasq

Configure Dnsmasq for your VPN

Pimp your LAN with OpenWrt & Dnsmasq

OpenWrt & Dnsmasq

Pimpin’ your dev env with Dnsmasq

Installing & Starting Dnsmasq

Configuring Dnsmasq

Top Level Domains – not just for the big-boys (anymore)

Pairing Dnsmasq & Apache Web Server