Explain to your Grandma: What is an Internet Exchange?

What would you do if external circumstances – like a worldwide pandemic and the shutdown of the whole society coming along – would force you to calm down? Moritz Frenzel, who works as Network Architect at Anexia, has used 2020’s springtime to work with his fellows on rebuilding the Internet Exchange Stuttgart-IX from scratch. Anexia supports this with providing hardware for the project.

In this interview Moritz explains, what exactly an Internet Exchange is, who needs it and why it feels good to do nonprofit work.

How would you explain to your grandma: What is an Internet Exchange?
Difficult task, but I’ll try: Actually, ‘the internet’ as such does not exist, but only a set of network providers, such as Anexia, Deutsche Telekom, Google, Facebook, etc. Each of these network providers can do whatever they want in their network to connect their customers to each other. But if a customer of Anexia wants to go to Facebook, we and Facebook have to connect our networks. There are 3 ways to do this:

• Anexia and Facebook connect with a direct cable (so called PNI, Private Network Interconnect). This is relatively simple, but somehow doesn’t scale that great if I want to reach all network providers in the world. Especially if the other network provider is a few thousand kilometers away.
• We meet at a central location, the Internet Exchange. Everyone plugs a cable into the switch there and then sees all the other connected networks via this switch. This is almost as good as a direct cable, but of course scales much better.
  Reaching a large number of network users directly with one cable scales much better and is also much more resource efficient.
• I commission someone to connect me to all network users in the world, so called IP Transit. This is also done via a cable, but what happens after that depends on the transit provider. It’s like you just buy ‘internet’ from your provider at home.

At the end of the day, every network enthusiast probably uses all 3 variants. IP Transit for far away destinations, Internet Exchanges for the multitude of providers in the region, and PNIs for a few with whom you exchange a lot of traffic.

Who needs such Internet Exchanges? Who are the customers of an Internet Exchange?
I think this follows a bit from my answer above.
Every network user needs local Internet Exchanges if they want to reach networks they currently access via their transit provider more directly. Compared to a transit provider, an Internet Exchange can score with lower costs, lower latencies and dedicated bandwidth. Likewise, the network provider then has direct control over his connections and does not have to trust the transit provider.

What is the Stuttgart-IX?
The Stuttgart-IX, or Stuttgart Internet Exchange, is a local Internet Exchange (IXP) that connects network providers in the Stuttgart region. Whereby ‘Stuttgart region’ actually includes the whole of Baden-Württemberg.

Why do we need small Internet Exchanges?
The size of an IXP is actually secondary, in my opinion there is no need for small or large IXPs. What is needed are regional IXPs.
The internet as such is decentralized, so if we were to build just one IXP for Germany, for example, and it fails, the whole of Germany would flap. However, if we give each federal state an IXP, and one fails, only 1/16 will flap. Of course, this also has an impact on latencies. If I have to go from Stuttgart to Frankfurt to reach someone in Reutlingen (about 30km away as the crow flies), this is of course slower than meeting in the Stuttgart region.
Of course, there is a sweet spot somewhere. One IXP per district and I come to the same scaling problem as one cable to each network provider, one IXP per country and I lose latency and resilience. Where exactly that sweet spot is, however, is a philosophical question.

You built your Internet Exchange from scratch in early 2020. What did you pay attention to in the process?
Stuttgart-IX has been around since 2005, but after one of the initiators and driving forces, André Scholz, unfortunately passed away far too early in 2015, the project came to a bit of a standstill and ran quietly for 5 years without anyone paying any attention. So, everything had to be dusted off and redone once, and since I had a lot of time in the first Corona lockdown in early March 2020, it was the perfect project against boredom. Even though Stuttgart-IX is run on a volunteer basis, we are used by real companies for real customers. So, the main focus was clearly on the stability and reliability of the infrastructure.
Furthermore, everywhere where network users talk to each other, the so-called Border Gateway Protocol (BGP) is used. This is basically a great protocol, but it has a catch: Basically, every network provider can send all IP addresses he wants to others, even if they do not belong to him. This is called route hijacks. With such connections (peerings), you always have to verify whether the IP addresses that the other network provider sends you also belong to him.
We want to be good internet participants and nip such route hijacks in the bud. We are therefore particularly proud to implement the specifications of the MANRS initiative. (Anexia is also part of the MANRS initiative, more on our blog, editor’s note)

What do your users take away from this rebuild?
A modern, stable and secure platform and, above all, a lot of commitment to expand the IXP. A lot has happened since the big rebuild at the end of April 2020, see also our news, and participants are benefiting.
Since the rebuild at the end of Q2/2020, we have also been able to triple our traffic, something we are of course particularly proud of.

There is a large community behind Stuttgart IX. How do you manage to get people involved in volunteering?
Only a handful of people are actively working, and that’s enough. Much more important is the community of our participants. It is always impressive what you can create when you work together. Stuttgart-IX is a platform for the Stuttgart region: seeing how we strengthen the region and the internet through our commitment is very motivating and satisfying.
Network providers can connect with each other through us, but also meet and exchange ideas at our local Beerings (meetups). Most of the time, this is not directly about Stuttgart-IX. For example, if a participant from Stuttgart wants to reach a customer on Lake Constance, she can exchange information with network providers on Lake Constance at our Beerings. If the participant and the provider then come to an agreement, they can then put the customer into operation via Stuttgart-IX (they don’t have to, of course).

What do you take away from volunteering at Stuttgart-IX?
Of course, I learned a lot about technology etc. with my work there, which is great and helps me professionally, but that’s secondary. Stuttgart-IX is a matter of the heart for me. I’m passionate about the internet, its security, its resilience, local peering and, above all, the internet community as a whole. Be it in my daily job at Anexia as a Network Architect, in my volunteer work at Stuttgart-IX or in DENOG e.V. – I love to make the internet better, but above all to connect people with each other.