How “National” is the Dutch Critical IP Infrastructure?

How “National” is the Dutch Critical IP Infrastructure?

This blog post is based on the report “Discovery and Mapping of the Dutch National Critical IP Infrastructure” by Fahimeh Alizadeh and Razvan Oprea.


After the publication of the Critical Infrastructure Protection report more than ten years ago, the leading questions that emerge today are how critical infrastructure companies are interconnected, how resilient are these connections, and to which extent are they dependent on foreign entities?

In 2002, the Netherlands started the Critical Infrastructure Protection (CIP) project with the objective “The development of an integrated set of measures to protect the infrastructure of government and industry”. In the CIP study, critical infrastructure includes the business enterprises and public bodies that provide the goods and services essential for the day-to-day lives of most people in the Netherlands. The critical infrastructure is divided into 12 critical sectors, with telecommunications and ICT as one of them.

In this blog article, we look into a specific aspect of the Dutch critical infrastructure, namely how the organisations part of the critical infrastructure depend on Internet services, and to which extent are these Internet services part of a Dutch national IP infrastructure. To this end, we map organisations part of the Dutch critical infrastructure to their presence on the Internet, and analyse how the organisations are interconnected via Dutch or foreign networks.

Previous Studies

The presence of organisations on the Internet is defined by the IP resources they use, and how their networks are connected with other networks. IP resources are the IP address blocks (IP prefixes) and autonomous system numbers (ASNs) that are used in a network. The interconnection between networks is governed by the BGP routing protocol, which operates with IP prefixes and ASNs in its routing/forwarding decision algorithm.

In 2012 in Germany, a joint project with two universities and the Federal Office for Information Security (BSI) classified the German “national Internet”. Their methodology started with the list of IP prefixes allocated to organisations registered in Germany. From this information they found the originating AS numbers and then their interconnections using BGP dumps.

We took a slightly different approach in our research — without access to privileged information (including, for instance, the IP blocks used internally by critical infrastructure organisations in the Netherlands), we were limited in scope. We however included in our analysis the foreign ASes that act as proxies for web and mail services provisioned by critical infrastructure Dutch companies.

Approach, Methods and Techniques

To discover and map the interconnections between the critical infrastructure organisations, we identify three phases in our analysis. First, we start by identifying the Internet presence: their AS numbers or the AS numbers of the entities that act as their proxies (think ISPs). Once the list was created, we looked at how are these ASes interconnected and, finally, we described a method for visually mapping them.

Finding the Points-of-Presence

The discovery part involved a lot of manual work — first we needed to find all the AS numbers assigned to Dutch organisations and then filter out those which are not part of the critical infrastructure. The data source used in the first step is an authoritative list maintained by RIPE NCC, containing all the AS numbers allocated to organisations from their service region, which roughly comprises Europe, Russia and the Middle East. Singling out Dutch organisations (not trivial) resulted in a pretty comprehensive list of 727 organisations. The next step was to filter the critical organisations from the list. We created a classification based on the 12 sectors the Dutch government deemed critical in CIP project. After filtering, we ended up with 335 selected entries — this was our bottom-up discovery process: from IP resources to organisations.

At this point we observed that around 80% of the organisations in our AS list are active in the Internet, IT and Communications sector. This meant that the vast majority of the critical infrastructure organisations used a “proxy AS”, such as an ISP to intermediate their Internet presence. This started the top-down discovery process. We selected a number of organisations from each critical sector (using Dutch Chamber of Commerce, Google, Wikipedia, etc.) and after a careful analysis we ended-up with around 150 entities.

Without having any information on the way organisations physically connect to the Internet, we relied on the public DNS data to extract the useful bits of information: the A (and AAAA) and MX records. Web and mail servers are important because inevitably there is a two-way information flow from and to the organisation to the entities hosting their web and mail servers (unlike the NS records for instance). The combined list obtained from concatenating the results of the two approaches gave us a master list of critical infrastructure-related ASNs.

Connecting the Dots

The next step was determining how these ASNs inter-relate. Two well-known Internet topology maps are from CAIDA and UCLA Internet Research Lab. These maps show all the links between AS pairs. For our analysis, we selected the UCLA IRL topology map as it was the most recent of the two.

In the initial mapping of the Dutch critical infrastructure, we selected all links for which both nodes are part of our combined list of ASNs (Dutch and foreign, discovered via the bottom-up plus the top down approaches). Unfortunately, the resulting graph had many disconnected nodes, which is an interesting observation by itself as it shows that the Dutch critical infrastructure is dependent on non-Dutch intermediary or transit nodes. The goal being to build the minimum graph that connects all the critical infrastructure ASNs, the next step was that for each ASN in our list we would add its provider (UCLA offered this information also) and re-run the selection process. In this way we ended up with a much better image on the relations between the Dutch critical infrastructure ASes and its dependency on foreign intermediary or transit networks.

The final step was to visualise this information in a way that offers an overview of the relations per critical sector but allows one to dive into more details if needed. For this study we considered Data-Driven Documents (D3.js) JavaScript library and Sigma.js library. For our purposes, Sigma.js library provided the visualistion methods that satisfied our needs: it gives a good perspective on each sector and allows one to zoom-in seamlessly in an area for details. By placing the foreign (proxy) ASes on the opposite side from the Dutch ones gave a even more intuitive representation of the AS interconnections.


We provided network graphs for each critical sector and used them as input data source for further analysis (our report contains more details). To give an example, let us consider the Energy critical sector, which includes 3 sub-sectors: electricity, gas, and oil. Figure 1 shows the ASN network graph for this sector when only direct links between each two ASNs are taken into account. No providers are included and it is clear that the graph is too disconnected to draw any conclusions. The distribution of links in two sides (Dutch ASNs on the right side and foreign ones on the left side), is divided almost equally: 44% for the foreign ASNs and 56% for the Dutch ASNs.

Figure 1: Energy critical sector without providers.

Figure 2 shows the graph after we add for each AS its direct provider — the graph is now more connected, with a different distribution of links: 69% for foreign ASNs and 31% for the Dutch ASNs.

Figure 2: Energy critical sector with providers.

Although it is expected that each node will have at least one link (it will be the connection of the node to its provider), we still can find one isolated ASN in the Dutch part — it is, according to RIPEstat, ASN 61013 (Alliander N.V.). Although Alliander N.V. is one of the largest companies in maintenance, expansion and adaptation of the gas and electricity network in the Netherlands, no IP prefix ever originated from this AS; instead their web server and mail server are hosted by British Telecommunications plc (ASN 5400).


In this research we mapped the representative Dutch critical infrastructure organisations using two discovery methods (bottom-up and top-down). The discovered organisations were verified manually one-by-one so we have a high degree of confidence in the accuracy of the results. However, we only worked with public sources of information and thus we did not see physical, private and back-up links. A more comprehensive list of organisations can only be obtained with specialised information, or with privileged access to information, which would allow us to know what IP address space is actually being used inside every organisation.

We observed that many critical infrastructure organisations have reliable connections to the Internet (the native and proxy ASes are well interconnected), but rely a lot on foreign providers for their communication needs.

If we would consider the imaginary scenario of an emergency in which critical sector organisations can only communicate using Dutch links, then around half of them (those that use foreign proxy ASes) would be cut-off from the network. In this context we find it would be useful to start a discussion regarding the security and privacy implications of having critical infrastructure organisations’ email and websites hosted with foreign entities, especially so with those from outside the European Union (EU) since they do not not necessarily have the same laws regarding data privacy and confidentiality.


The study was performed as a System and Network Engineering (UvA) Master thesis research project by Fahimeh Alizadeh and Razvan Oprea under supervision from Benno Overeinder (NLnet Labs) and Marco Davids (SIDN).