We mostly view the internet as something decentralized and resilient. And from practical point of view, it almost is. The Web is decentralized – websites reside on many different servers in many different networks and opening each site does not rely on a central server or authority. And there are all these cool peer-to-peer technologies like BitTorrent and Bitcoin that do not rely on any central server or authority.
Let’s take a look at these two examples more closely. And it may sound like common sense, but bear with me. If you don’t know the IP address of the server, you need to type its alias, i.e. the domain name. And then, in order to resolve that domain name, the whole DNS resolution procedure takes place. So, if all caches are empty, you must go to the root. The root is not a single server of course, but around 500. There are 13 logical root DNS servers (lucky number for the internet), operated by 12 different companies/institutions, most of them in the US. 500 servers for the whole internet is enough, because each intermediate DNS server on the way from your machine to the root have caches, and also because the root itself does not have all the names in a database – it only has the addresses of the top level domains’ name servers.
What about BitTorrent and Bitcoin? In newer, DHT-based BitTorrent clients you can even do full-text search in a decentralized way, only among your peers, without any need for a central coordinator (or tracker). In theory, even if all the cables under the Atlantic get destroyed, we will just have a fragmented distributed hash table, which will still work with all the peers inside. Because these Bit* technologies create the so-called overlay networks. They do not rely on the web, on DNS or anything else to function – each node (user) has a list of the IP addresses of its peers, so any node that is in the network, has all the information it needs to perform its operations – seed files, confirm transactions in the blockchain, etc. But there’s a caveat. How do you get to join the overlay network in the first place? DNS. Each BitTorrent and Bitcoin client has a list of domain names hardcoded in it, which are using round-robin DNS to configure multiple nodes to which each new node connects first. The nodes in the DNS record are already in the network, so they (sort-of) provide a list of peers to the newcomer, and only then he becomes a real member of the overlay network. So, even these fully-decentralized technologies rely on DNS, and so in turn rely on the root name servers. (Note: if DNS lookup fails, the Bit* clients have a small hardcoded list of IP addresses of nodes that are supposed to be always up.). And DNS is required even here, because (to my knowledge) there is no way for a machine to broadcast to the entire world “hey, I have this software running, if anyone else is running it, send me your IP, so that we can form a network” (and thank goodness) (though, probably asking your neighbouring IP range “hey, I’m running this software; if anyone else is, let me know, so that we can form a network” might work).
So, even though the internet is decentralized, practically all services ontop of it that we use (the web and overlay-network based software) do rely on a central service. Which fortunately is highly-available, spread across multiple companies and physical sites and rarely accessed directly. But that doesn’t make it really decentralized. It is a wonderful practical solution that is “good enough”, so that we can rely on DNS as de-facto decentralized, but will it be in case of extreme circumstances?
Here are three imaginary scenarios:
Imagine someone writes a virus, that slowly and invisibly infects all devices on the network. Then the virus disables all caching functionality, and suddenly billions of requests go to the root servers. The root servers will then fail, and the internet will be broken.
Imagine the US becomes “unstable”, the government seizes all US companies running the root servers (including ICANN) and starts blackmailing other countries to allow requests to the root servers (only 3 are outside the US).
Imagine you run a website, or even a distributed network, that governments really don’t want you to run. If it’s something that serious, for example – an alternative, global democracy that ignores countries and governments – then they can shut you down. Even if the TLD name server does resolve your domain, the root server can decide not to resolve the TLD, until it stops resolving your domain.
None of that is happening, because it doesn't make sense to go to such lengths in order to just generate chaos (V and The Joker are fictional characters, right?). And probably it's not happening anytime soon. So, practically, we're safe. Theoretically, and especially if we have conspiracies stuck in our heads, we may have something to worry about.
Would there be a way out of these apocalyptic scenarios? I think existing overlay networks that are big enough can be used to "rebuild" the internet even if DNS is dead. But let's not think about the details for now, as hopefully we won't need them.