When your business hinges upon remote workers and remote offices, secure connections, and lots of data manipulation… how do you deal with some of your folks being extra remote? Granted the internet in 2020 is very different from the internet in say 2008 and the world has grown ever smaller as a result… but distance and all of the congested, intervening, network hops that come with it are still a reality. Particularly for remote workers living on other continents that have to interface regularly with systems in the United States as a part of their job.

The two big headaches for remote workers in other countries connecting to offices in the US are latency and bandwidth. In the past there were only and handful of solutions, most involving long-term contracts with a telcom and lengthy, complicated setups. I would argue that MPLS still falls squarely in this camp. SD-WAN has certainly improved on all of the above but it’s still enough of a headache that it typically involves contract terms and conversations with sales “engineers.”

I would like to propose something different using Azure.
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The current state of the world has caused some unique stresses on IT infrastructure. For IT departments servicing internal teams, remote access infrastructure in particular has felt the brunt of the blow. To that end, I spent a couple of weeks testing out enterprise VPN solutions.
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I have been taking a free networking class from Stanford University’s online “open source” education platform. I have really been enjoying the first unit of the course as it has started filling in some gaps in the foundation of my understanding regarding networking, the internet, and TCP/IP. I highly recommend this to anyone that has been in IT for a while but has never taken a more “academic” approach to their work. Okay, so that is my plug for free education. You can check out more here if interested: https://lagunita.stanford.edu/

OSI 7-Layer Model, TCP/IP 4-Layer Model
One of the gaps in my understanding of networking has to do with the OSI 7-layer networking model and the more simplified TCP/IP 4-Layer model (which was developed by DARPA? and predates the OSI Model). I didn’t even realize there was anything other than the 7-Layer model until taking this class and furthermore didn’t realize that while the OSI model gets talked about and referenced more frequently, academia (I think… and perhaps the industry) is shifting to using the simpler 4-layer model for discussion, understanding, and development regarding networking. Please don’t take any of this as gospel truth, this is just my understanding based on coursework and reading. I also find it much easier to think about and reference the 4-layer model. If you are curious how the two compare, this technet article is an interesting read, Technet: TCP/IP Protocol Architecture. Okay, so for this article, I will be sticking with what I am most comfortable with at this point and will be talking about and referencing the 4-layer TCP/IP model and discussing how VPN works. (more…)

Open VPN Access Server uses NAT (Network Address Translation) to “ease” routing VPN user traffic to the rest of a remote network. This isn’t always a desirable configuration.

If you want to disable NAT globally, you can do so by logging into the shell as a root user on your OpenVPN Access Server and doing the following:

cd /usr/local/openvpn_as/scripts
./sacli --key vpn.server.nat --value false ConfigPut
./sacli start

This globally disables NAT on the box and you can then use routing tables on your network to manage traffic flow. This is handy when you already have an established network with a device (or two) that are handling routing for you and will definitely fit some use cases.

For clarity’s sake I will go ahead and state the following: This is for OpenVPN ACCESS SERVER, not for the open-source/free community edition. They are very different beasts so take note of which you are using.

References:

https://docs.openvpn.net/docs/access-server/openvpn-access-server-command-line-tools.html