I've been using split-horizon DNS for years…and I've hated every minute of it. I hate having to maintain 2 sets of DNS records that refer to the same damn resource. It is my personal definition of “pain in the ass”. Recently, I started working with the Unbound resolver, and more specifically, the Python scripting module implementation it has. I was playing around with this for a project at work and it occurred to me while I was doing that, here is my answer to the plague that is split-horizon DNS.

I took it upon myself to write a nice little module that allows you to map external A records to internal IPs. This allows you to set up your external DNS names for “www.example.com” that point to 1.2.3.4, but is actually the web server on your internal network at 192.168.1.100.

The goal here is to walk you through setting up ub-split-map with a basic Unbound configuration to let you have a modern, fast internal resolver that transparently maps your external to internal addresses.

I'm not going to go into a lot of detail here; I assume anyone who has made it this far has some basic *nix technical knowhow and can do things like install necessary packages, etc.

I'm not going to say a lot here, but make sure you have Unbound installed with the Python module. You'll want to do one of the following:

sudo apt-get install unbound python-unbound
sudo yum install unbound unbound-python
USE=python emerge unbound
./configure --with-pythonmodule

That's it for now, we'll come back to configuration of unbound in a bit.

There's a lot of ways to do this as well. You can download the source from github, clone the git repository from github or use easy_install or pip to install it.

I'm going to assume you know how to download and unzip file. Once you have the ub-split-map-x.x.x dir. Do the standard Python install routine:

cd ub-split-map-x.x.x
sudo python setup.py install

This is pretty simple if you either have easy_install or pip installed.

sudo pip install ub-split-map
# OR
sudo easy_install ub-split-map

This is going to take a little bit file finding in order to get set up depending on how you installed ub-split-map and how your system is configured, etc., but it's not too difficult.